Great presentation! Is there a way that a NANO VNA can output it's choke results in the magnitude of "Z" rather than dB?
@darylcheshire161816 күн бұрын
I tried to make a 1:1 today but my toroid seem to be smaller than all those yt examples.
@johnbeaurain156727 күн бұрын
Thanks a lot for this video, now it is clearer for me, except that you speak fast and for a non-english-speaker it's not easy to understand but i've seen it two times and it's ok now !😁
@kenh897929 күн бұрын
That's a GREAT video explaining Common Mode Chokes - One thing, you never talk about power handling ability since these are usually used with TX as well as RX situations. The air core coax wound chokes would be limited only by power handling of coax, or close depending on how much capacitance affected power handling. The ferrite cores would be my concern - I think even the clipon ferrites would handle 100 watts, but when 1000 watts is involved it would require more?
@ChaplainDaveSparks2 ай бұрын
A question just came up in my mind: If you use two ferrites in series, does the separation between the two matter? IOW, does the flux from each one couple with that of the other one? I think I'll start saving up for a VNA. Also, I'm curious about one other thing *(NOT* related to coax). If I buy a pre-made common mode choke, can I connect one of the sets of windings backwards and turn it into a *DIFFERENTIAL* mode choke? How would that compare with using two *separate* inductors (wound on *different* cores) for that purpose? _73 de AF6AS_
@ChaplainDaveSparks2 ай бұрын
_Cal Poly?_ Which one? I graduated from _Cal Poly, Pomona_ in 1976 with a BSEE. _73 de AF6AS_
@fnordist2 ай бұрын
What would happen if one were to place the common mode choke in an iron or aluminum tube? For instance, if someone were to insert a linear common mode choke into the support mast itself to protect the coaxial cable from weather elements like UV rays? What are the potential impacts, and have you ever measured them?
@brianholmes34512 ай бұрын
Is Halibut Electronics going to be at Dayton this year?
@NamasenITN2 ай бұрын
BTW: engineers do not build e.g. bridges by a "trial and error" approach 😅
@ap2ms3 ай бұрын
I'm new to the hobby . . I have made a choke balun which i want to use near my HF radio, It is made of 240 mix 43 toroid and RG-58, my question is: is the distance between the balun and HF rig critical ? jumper i made will give me 8 inches distance b/w choke and radio
@roryr6794 ай бұрын
These are the answers about common mode that I have been looking for , for a long time. great lesson, thank you
@SmittyHalibut4 ай бұрын
I'm glad it helped. 🙂
@DonzLockz5 ай бұрын
Top presentation, graphics and explanation! I am yet to play with my VNA and just got some 31 mix torroids for this exact purpose. I have not seen anything like that test box but would like to build one. I have bookmarked the video for playlist to build. Perfect timing, thank you!👍🤠🇦🇺73 de VK1DON
@SmittyHalibut5 ай бұрын
Funny you should mention wanting to build a CMCC Test Rig. When I recorded this, I hadn’t yet started my own company. I now sell those kits. electronics.halibut.com/
@watthairston14836 ай бұрын
Very good presentation and treatise of one of the most prevalent ham station basic problems....
@halibutelectronics6 ай бұрын
Thank you. :-)
@ronbennett55916 ай бұрын
Forgive my late input . I note in a few of the comments that many would love to see a comparison against a Coax bottle type Choke and what the attenuation figures come out like . . Great video by the way . Well done 73. Ron G4DIY
@SmittyHalibut6 ай бұрын
Thanks for the positive feedback! I'm not sure what design you mean by "Coax bottle type choke". A quick google search turned up a design where you wrap coax around a pill bottle? Is that what you mean? If so, that's just an air-core choke. The bottle is only a form to wrap the coax around, but doesn't appreciably impact the magnetic permeability of the choke. If you mean some other design, please point me to a page or article describing what you mean.
@ronbennett55916 ай бұрын
@@SmittyHalibut hi there again. Well my “bottle type “ is literally a plastic bottle about 8 inches high and about 4 inch diameter . I have coiled Rg 213 Coax around it with about 20 turns . So its a coaxial choke effectively.
@SmittyHalibut6 ай бұрын
@@ronbennett5591 Ok, yeah. So it's an air-core choke. I've gotten feedback elsewhere in this comments section that I never gave a properly-wound air-core choke a fair shake, and that's true, really. I need to make an update to this video with my CMCC Test Rig kit instead of the hand-built test rig in this video; when I do that, I'll give an air-wound choke a proper test.
@miranovak80986 ай бұрын
Hi, I find that a 1:1 choke will degrade my reception by 1-2 S. Is this ok? I have a choke on a toroid with 121 turns of coax
@SmittyHalibut6 ай бұрын
121 turns! That seems excessive. Depending on what coax that is, you're probably just seeing the loss of so much added coax in your feedline. If that was supposed to be 12 turns, that's much more reasonable and at that point, I suspect something is wrong with the choke. A properly functioning choke should have zero impact on the normal reception of your antenna system, except the added loss of the additional feed line in the choke itself. But that should be around 1dB for moderate coax, and less than that for good coax. It'll be WAY less than 1 to 2 S units (an S unit is 6dB, so that's 6 to 12dB!)
@miranovak80986 ай бұрын
Of course 12 threads. RG58 on FT240-43 toroid. Attenuation according to VNA 25-35db. There's nothing wrong with that. On ft8 lower report. When SSB calling kiwisdr, I can hear myself much more faintly. I don't understand why that is. Where can I go wrong? @@SmittyHalibut
@SmittyHalibut6 ай бұрын
@@miranovak8098 attenuation, using my test rig to measure the common mode of the choke? Or just connected directly to the VNA? If you’re using the adapter described in the video (that I sell now, electronics.halibut.com) then 25dB common mode loss is good, but that’s not what you need to measure for reception loss. Connect your choke directly to the VNA, no adapter. And measure the S21 LOGMAG on that. That should be 0dB loss, or very close to it. If it’s higher than 0dB, something is very wrong with the choke.
@J-MR.6 ай бұрын
The coax might be damaged by the winding process ?
@SmittyHalibut6 ай бұрын
It might be, depending on the cable. Thats why I use RG316, which has a very small minimum bend radius, for winding on FT140 cores. Larger coax on larger cores, you definitely should not abuse the minimum bend radius. It’s possible that’s what’s happening here on @miranovak8098 ‘s choke.
@ve6kk6 ай бұрын
Excellent explanation and test work Mark. As another RF guy I am troubled by 2 things. One at 09:20, how can CM noise get inside a shielded radio when applied between coax shield and transceiver "ground"? I suspect all CM noise entry is either via poor coax or transceiver shielding. Two at 22:03 is the assumption that a CM choke should be X times the cable Zo. I doubt that the surge impedance on the outside of the coax is also 50 Ohms. Anybody wiser?
@SmittyHalibut6 ай бұрын
1: you’re probably right that RF gets in on bad coax too. Heck, it’ll get in on the antenna itself! But any non-perfect ground will also put that noise into the receiver. 2: The goal is to make the common mode impedance as high as possible at the target frequency. Common wisdom as proposed by people smarter than me is “about 1000 ohms.” That’s about 20x a 50 ohm system … and I think I’m realizing I did my dB math wrong in the video. That’s 20x impedance (linear with power), not 20x voltage (square with power). So it’s only 13dB, not 26dB. If I’m right, all the numbers I gave in the video are twice as good as they “need” to be. Huh. Well, we have some mighty fine CMCCs out there I guess.
@ve6kk6 ай бұрын
@@SmittyHalibut Yup I agree with the math. Just the relation to 50 Ohms which is the internal cable Z not the outside "third wire". No matter, we need Z as high as possible, in most cases with a good Rloss to gobble up energy. As far as RX CM I think it is an "all cables" sneak in (line cord, USB, LAN...). CM chokes DO help. But as for TX induced RF chokes should be at a voltage maxima on the line where ever that it is. PS It is amazing how far the ham community has come in understanding lines, VNAs etc. Cheers!
@reedjasonf7 ай бұрын
I took issue with the description of a coax as a differential cable early on in the talk (around 4 minutes). Signal Integrity engineers refer to them as single ended for a reason or two - a differential cable, for example requires at least 4 vna ports set into 2 logical port groups; and the shield is not the return conductor, it is a shield. It serves the same purpose as the shield over a twisted pair like in an ethernet cable, which is a true differential system. One more comment is that shields of coax are almost always tied to the chassis ground on both sides, not the signaling elements of a transceiver so there is no push-pull of currents. Any differential currents created are simply inductive coupling between the center conductor and the shield. That all said, I love the data collected on the experimental chokes the nanoVNA plots. I wish we could have seen data for 2 chokes placed on a single gordian knot to see how adding chokes improved the common mode rejection also.
@SmittyHalibut7 ай бұрын
I just re-watched that section to make sure I was thinking about the right thing. You are absolutely correct that there is a world of difference between a Single Ended signal (like on coax) and a Balanced signal (like on twin lead, or twisted pair). But that's more about voltages, not currents.. (Yes, voltages which then drive currents though impedances, yes, so it's not entirely NOT about current... See below...) But even a Single Ended signal will have opposite and equal current flows on the coax. My mistake was referring to those currents as "balanced", little b, the adjective. They are not Balanced, big B, the proper noun describing the signal type. That's why it's called Differential Mode for currents, because that's different than Balanced for voltages. The push-pull of currents part, again, you are correct. That's the impact of a Balanced (big B) signal on the currents that we talked about earlier. But that still doesn't mean that there isn't an equal and opposite current flow on the feed line. If there's no other return path for current, it HAS go to on the feedline. And even if there is another return path for current, like you said, it will induce the return current in the coax and probably prefer that path over the other (assuming your coax is well connected and low impedance compared to the alternate path.) So, you're not wrong in any of your response. But I think those points don't really impact the description of the examples presented.
@Hidden_Destinations7 ай бұрын
FANTASTIC tutorial. 30+ year BSEE and Electromagnetic major here. You know your subject and can present it well. Thank you for all the work put into this.
@SmittyHalibut7 ай бұрын
Thank you! I appreciate the kind words. :-)
@reedreamer95187 ай бұрын
I too have done some research and testing to determine the optimum ferrite materials and number of turns to get the most out of my RFI choke filters. I based my conclusions on ferrite manufacturers equations and my personal tests using signal generator, oscilloscope and nanoVNA to sweep the entire HF band (e.g. building a combined differential and common mode filter for the output of a home-brew DC switching power supply for my shack). I too found that, for a snap-on ferrite, 0.5 inch hole, type 31, 3 turns was optimal before capacitive coupling between turns reduced effectiveness. But for an FT-240-31 I think 5 to 7 was optimal, according to manufacturer's equations and testing (this was 3 years ago so I don't quite recall exactly). However, I also built a 1:1 current balun for use as a wire dipole feed point and I put 11 turns (16 AWG PTFE insulated wire, split and wound in two direction) on that one, and it tested extremely well, -35 dB attenuation across most of the HF band. So it seems the geometry of the toroid makes a big difference in terms of how many turns is optimal. And your tests also showed better braud-band attenuation with the 13 turns around a FT-140. Do you have a general explanation for this? Why does the capacitive coupling add up so much with the snap-ons?
@SmittyHalibut6 ай бұрын
Its more about the turns of cable than the ferrite material. When on a torroid, the turns are spread out, more space between windings. When wrapped in a "Gordian knot", they're immediately adjacent to each other, maximizing the capacitance between turns.
@bill-20187 ай бұрын
I never bothered with chokes at one time but decided to try ferrite rings a few years ago. I looked at the G3TXQ site for information which rings to use and how many turns to use for a particular range of frequencies. No dipole of mine has ever been in the clear and my inverted vee is squashed into a 25' x 12' garden but, hey, it works! The first was on my 60m inverted vee at the aerial. It didn't seem to do much to stop r.f. getting down the coax and back into the shack. I then tried it inside the shack and it did stop r.f. getting back. I put two more at the aerial ends of my two coax cables to my five 20m to 10m dipoles in the attic. I did the same with these and put them in the shack. These are now in the shack as well. I came to the conclusion that r.f. was getting onto the cable after the choke so they might be better lower down the coax. If you think how long a wavelength is it can easily get on the coax below the choke. I've seen two aerial manufacturers say these two different things about where to put them. I also thought that two chokes, one at the aerial and one close to the tx might be a good idea. G4GHB.
@websurferx8 ай бұрын
Another benefit of the OHIS is user experience and ease of use. How many times have you purchased a headset or mic and didn't get the right adapter, or had to build your own adapter? How much time have you poured over pinout diagrams or relied on vague descriptions from some log forgotten blog post? Did you read the pinout backwards? Oops. Time to rewire or buy another connector. The user experience improvement benefits both device and radio makers.
@Frankey23108 ай бұрын
16:00 - outer conductors of the two NanoVNA ports (at least on the old 1.5G one, the one made out of three SA612A mixers) are shorted through the device's common ground, just FYI
@SmittyHalibut6 ай бұрын
True. That would make the plane of testing right at the edge of the VNA, including the cables between the VNA and the test rig, which is ... less than ideal... 🙂
@revbikerbigd86648 ай бұрын
Excellent video brother
@espenskog87459 ай бұрын
Thank you. Very nicely made and easy to understand.
@clems69899 ай бұрын
Dude, you need to make more videos ! Good Job !
@SmittyHalibut9 ай бұрын
:-) Thank you.
@tlebryk9 ай бұрын
What if the coax has two shields, one inner foil and an outer braid?? Does that mean 5 currents?? How to wire up an RF choke with toroid ferrite??????
@SmittyHalibut9 ай бұрын
If the foil and braid are touching, then no, consider that a single shield. If there’s a layer of insulation between the inner and outer shield, then you have a special coax that’s designed specifically for keeping differential mode and common mode currents separate. I’m not an expert on these, but I think the goal is to ground the outer shield to the chassis at the transmitter and leave it disconnected at the antenna. It’s basically a shield for the feedline. Then the inner shield can be connected directly to the transmitter amplifier ground reference (not the chassis), and the antenna. It’s a more complex transmitter arrangement. If you don’t have that, then just connect both shields to the transmitter, and only the inner shield at the antenna.
@haxwithaxe10 ай бұрын
I think this is a good idea and not just for hams. There are plenty of devices with unusual audio interfaces outside of ham radio. Not as common but they're out there. I'm skeptical of the idea that manufacturers will put this interface in radios because my understanding is they make a big chunk of money off of selling accessories and if they have to compete for accessory sales they will be financially up a creek.
@SmittyHalibut10 ай бұрын
I've spoken with a few manufacturers and I categorize their response as Optimistic Skepticism: "That's a really great idea! I don't think it'll ever happen." :-/ I actually think it's not that bleak. Your point is totally valid, but OHIS doesn't have to REPLACE their existing ecosystem. I'm not asking the big three to do away with their GX16 mic connectors, but to add an OHIS port next to it, or maybe on the back of the radio. They already have the "Accessory" port which duplicates the audio in and out and PTT, so I know they CAN do it. The trick is convincing them that it's WORTH doing with a standard. And the way to do that is to get traction on that standard. So that's what I'm trying now.
@ricktighe19110 ай бұрын
Very cool...and timely. It would be nice to add the CW Keying Line...but all out of pins, (maybe in CW mode the PTT line becomes the keying line). My interest is in being able to easily SWITCH between radios in my collection of rigs. I've just completed a modular desk project that allows me to physically arrange the equipment for ease of access. This standard helps tremendously with the switching project, even though my rigs' manufacture dates span decades. I look at the "Adapter Project" as a retrofit solution for legacy equipment. If all radio manufacturers, starting tomorrow, were to equip their radios, with OHIS ports and the headset, mic PTT switch manufacturers released their products with OHIS plugs, obviously no adapters would be needed; hence my view of the current status as a retrofit of legacy equipment. Various attempts have been made to produce products for RIG selection, but none that I've seen have taken the 40,000 foot view that you have...great work!
@SmittyHalibut10 ай бұрын
Thank you for the kind words! 🙂 This video is intended as a generic standards advocacy video and doesn't touch on the devices my company Halibut Electronics makes. I'm currently selling adapters (pre-sale, delivery in October 2023), and am working on two "Consoles" to go between the radio and the user. The first is the Contesting Console (two users, one radio), the second is the Station Console, which is what you're describing: multiple radios, one user. It's expected for release sometime in the first half of 2024. And, yes. Ideally, manufacturers would adopt OHIS and start putting OHIS ports on their gear natively, no adapters necessary. But I acknowledge that they are unlikely to do that until there's some traction with the standard. Adapters are the bridge technology to get us there.
@thuff320711 ай бұрын
Good idea but how about a bluetooth interface with it too.
@SmittyHalibut10 ай бұрын
The standard is just the electrical middle part. The devices that implement that standard is where the Bluetooth would be. There's nothing stopping anyone from making a User adapter that connects to a Bluetooth headset instead of a cabled headset. Or a Radio adapter that LOOKS LIKE a Bluetooth headset and presents an OHIS Radio port. I'm not sure how standard the Bluetooth PTT stuff is though, how difficult that would be to implement. I'm currently concentrating on wired analog solutions and haven't really researched the Bluetooth stuff yet.
@thuff320711 ай бұрын
Nice presentation and it makes sense to test any balun before use to actually know what you are getting. Thank you and now I need to test.
@SmittyHalibut6 ай бұрын
I know I'm kinda late (apparently not getting notifications for many of the comments on this video!), but I will point you to electronics.halibut.com/product/common-mode-current-choke-test-rig/ 🙂
@jakedillingham11 ай бұрын
Excellent thank you very much
@ernestb.237711 ай бұрын
Thanks for the video. As I was watching I was wandering about influences of possible phase shifts in the device. The influence on the working of the common mode choke. Signal coming in the choke (on one side) and signal comming in (on the opposite side and from the opposite direction) may have some phase shift. The load is probably not pure resistive....
@SmittyHalibut11 ай бұрын
Are you talking about the Differential Mode response, meaning how transparent it looks to the signals flowing through it? Or the Common Mode response, meaning how the phase affects the resistive/reactive balance of the impedance it imposes? If the former, the Differential Mode view, by definition Differential Mode currents sum to zero through the inductor, so there is no impact at all. When I=0, it doesn't matter what the j component of X is because it will be multiplied by 0 to get your V vector. "What if phase differences result in I!=0?" Then those differences would become Common Mode. By definition. If the latter, the Common Mode view, then yes you're absolutely right. The impedance imposed by a Common Mode Current Choke is not purely resistive across the whole band of interest. It's an RLC complex circuit. An IDEAL choke would be all R and very little LC over the whole band of interest, but that's nearly impossible. In the video I show highly resonant chokes with a very deep attenuation "peak" (shown as a "valley" on the graph because it's a negative number). In those cases, if you measured the Complex Impedance of the CMCC, you would see a high R/low X at that peak, because that's the resonant point of the choke, and resonance at the frequency happens when f*L and f*C are equal but opposite, which cancels them out and leaves you with nothing but R. But outside that peak, the response becomes very reactive.
@BusDriverRFI11 ай бұрын
Electrically speaking, what's the difference between balanced and unbalanced?
@SmittyHalibut11 ай бұрын
Balanced means the voltages go up and down relative to ground on BOTH wires, with the same signal but inverse of each other. The average voltage is always 0, always ground. This is what you have on twin-lead feedlines like ladder line, or XLR mic cables. Unbalanced means one wire is ground, a fixed voltage, and the other wire goes up and down relative to the ground reference. This is what you have with coax like UHF/BNC/N connectors, or RCA audio cables. There are some special cases that I’ll ignore here (like “pseudo balanced,” and phono (as in record players) signals which can be treated as balanced, despite the use of RCA connectors.)
@SmittyHalibut11 ай бұрын
Balanced and unbalanced has to do with the voltages. This is not to be confused with differential mode and common mode, which has to do with currents. Differential mode currents are when the current flowing in each wire of your transmission line are exactly balanced. The same amount of current flowing in both directions. The sum of the currents is zero. Common mode current is any difference between the currents in the transmission line. If the sum of currents is NOT zero, the bit that is not balanced between the two wires is the common mode. For example: if there’s a transmission line, two wires, whether balanced or unbalanced, and one wire has 2A flowing one direction and the other wire has 3A flowing the other direction, then there is 2A of differential mode current and 1A of common mode current.
@BusDriverRFI11 ай бұрын
@@SmittyHalibut so you're saying that the voltages go up and down relative to ground in both wires. So if I power my transceiver with a center tap transformer so that the ground is between the pl 259 shield and the other side, the shield and the center conductor will be equal voltages 180° apart and therefore balanced? How does that change the operation of my transmission system in the long run? What does it matter where my reference ground is electrically?
@SmittyHalibut11 ай бұрын
@@BusDriverRFI Don't do anything to the AC power input on your radio. That will cause all kinds of damage. A given transmission line is either balanced or unbalanced. Coax is inherently unbalanced, twin-lead is inherently balanced. If you want to convert from one to the other, you use a (real) Balun (not the things a lot of people claim are baluns.) There are a few reasons one would choose a balanced transmission line over unbalanced. Balanced transmission lines have less loss than coax; for VERY high powered systems (100kW and more), coax becomes large copper pipe and becomes incredibly expensive, where balanced transmission lines can still just be large gauge wire. For hams, a well deployed balanced signal can also be better at eliminating common mode noise than coax. This can be useful on receive. The downsides to a balanced signal is that its fields extend past the boundary of the cable itself, whereas coax is entirely contained inside the cable. This means you have to be very careful how you deploy balanced cable: If you put anything close to the cable that interacts with the E and M fields (eg: running it close to a metallic tower), it will impact the signal. So you have to space it away from near by stuff, including other balanced transmission lines. You don't have to do this with coax: You can tie it immediately to the tower, next to other coax runs, power cables, whatever. It doesn't matter because all the RF is contained entirely inside the shield. Weighing these pros and cons, most hams are running low enough power and good enough coax that the disadvantages of balanced feed lines outweigh the advantages. So most of us use coax. But you see balanced feed lines a lot more in much larger installations.
@BusDriverRFI11 ай бұрын
@@SmittyHalibut seems strange that a 1:1 could cause all kinds of damage. I wasn't going to do that anyway because I don't want high voltage on my radio case. It was a hypothetical question and not a practical question as to determining whether the "unbalanced" line would be considered "balanced" if it was fed with the "balanced voltage" input. Seems logical that since we are talking about the voltage being balanced, the thing keeping coax from being balanced is the input biasing.
@octavs_ER1SKI Жыл бұрын
built one as well, as per your istructions (the version with the switch). works as a charm! maaany thanks!!!
@SmittyHalibut6 ай бұрын
Yay! I'm glad to hear it! 🙂
@rickeaston3228 Жыл бұрын
You need to relearn your theory. An inductor does NOT stop the flow of AC or RF current no matter what inductive reactance present. What stops and attenuates common mode is resistive parallel resistance that dissipates the common mode. An inductor does not consume power it just changes it's phase. Cores create this resistance within the core characteristics.
@ac7fd3 ай бұрын
Thanks for the constructive input. I‘m sure Marc appreciates it 👍🏼 It helped me understand it better.
@airheadzradioadventures Жыл бұрын
Alright, you just put all the pieces of the puzzle together. Fantastic work and presentation. Following.. Thank you so much!
@SmittyHalibut Жыл бұрын
I’m glad I could help. :-)
@enojelly9452 Жыл бұрын
Great talk. Thinking about getting my ham license, but I think I’d be in the “mostly building, not operating” group as well. What are POTA and SOTA?
@SmittyHalibut Жыл бұрын
“OTA” usually means “On The Air” so it’s just a matter of the first letter(s). POTA is Parks, and SOTA is Summits. Both their websites can be found by searching. (Read: I don’t remember the URLs off hand. :-)
@rv6amark Жыл бұрын
First of all, nice video, one of the best I've seen on building a CM choke. Only one minor comment: "Building something and trying it" is NOT really an "engineering approach". It is actually an "experimental" approach. As an engineer for 43 years, I found that taking an "experimental approach" ended up taking up a lot more time in the "development phase" of a product than working the design out mathematically before laying any lines down on a drawing. Having said that, I frequently approach my amateur radio projects as experimental in nature simply because I like building a lot more than I like math. In amateur radio I am not bound by schedules, budgets, difficult test requirements, etc, so I can enjoy the build to "see what I end up with". So, this is not meant to be a negative comment about your video. I found your explanations were clear and accurate with nice visual aids, and more importantly easier to understand than wading through the math. Good overview on setting up and using a VNA, too. --Mark, KE6BB 👍
@SmittyHalibut Жыл бұрын
That’s a fair point. I think what I was trying to say was “practical” vs “theoretical.” To me, that’s the difference between engineering and science. Engineering is more applied, science is more conceptual. But you’re right, “experimental” is an even better term for what I’m doing here. Thanks for the feedback! :-)
@PPGATL Жыл бұрын
Awesome stuff! When you talked about calculating or experimenting with Gordian Knots to make a choke for a specific band, I had to comment because I've done exactly that. I fly paramotors, wanted to build an antenna for GMRS (462 MHz) out of a chunk of RG316 with half of the coax sheath removed, then string it up one of the glider lines. 2 problems: 1) "Center/core fed vertical" doesn't resonate well on any frequency. Experimenting showed that the angle between the two legs needs to be around 30° (aIrc) for resonance, and 2) Even if I got it resonant, Instill needed to decouple the antenna from the feed line, otherwise the radio body, the hand holding it, any metal or human near the coax would cause wild swings in the SWR. So I added a Gordian Knot, and experimented until I reach both resonance and decoupled the antenna from the feed line. In my case there was 2 loops at around 6cm diameter. Location of the knot along the coax was also critical. Couple of us flew those antennas for a while and they worked well but wore out quickly. Next version will be with more flexible coax, and the knot up higher on the line so it won't get beat up as badly during handling. Also trying to figure out how to do multibands ...lol
@SmittyHalibut6 ай бұрын
That's awesome! (Sorry for the late reply; not sure why I didn't get a notification for this one.) Gordian knots can work well for mono-band operations, if you tune them. And a rig like described here can help you do that. But they are inherently mono-band.
@klumpy103 Жыл бұрын
Neat work, you do need to have an understanding of the basic physics, but really, what better way than showing by practicality what effect any changes would have on your desired output. I have nothing to do with ham radios but even i understood the whole concept as presented. Well done.
@SmittyHalibut Жыл бұрын
Thank you for the kind words. 🙂 And, if you ever decide you want to get your ham radio license, KZread (and the Internet as a whole) has a whole lot of resources to make that happen. Just let me/us know, and we'll point you in the right direction. Cheers!
@acestudioscouk-Ace-G0ACE Жыл бұрын
Thanks for this video, as a returner to the hobby after nearly 40 yrs, it was very useful to me. Forgive me if this is a dumb question but please would you confirm that when you say "outside" you mean outside edge of the shield and not the outside plastic sheath of the coax? I ask this because I know you can get RF burns from the very outside of the plastic sheath of a coax. Thanks again.
@SmittyHalibut Жыл бұрын
Not a dumb question at all! The currents are traveling on the shield, that is true. But RF can capacitively couple through the insulation into your skin. If the currents are high enough, then yes you might get burned (more likely a tingle) from touching the coax. Now, that’s a REALLY BAD common mode current. If that’s happening, something is seriously wrong with the antenna or feed system. Under normal circumstances, with normal levels of reflected common mode current, it’s very unlikely you’ll get an RF burn by touching insulated coax. But once that current hits the metal chassis of the radio, or the shielded-not-insulated microphone that’s in your hand, you’re much more likely to feel even small to moderate amounts of current. Get thee a CMCC post haste! :-)
@acestudioscouk-Ace-G0ACE Жыл бұрын
@@SmittyHalibut Thanks so much for your detailed reply, it all makes sense now. I had not thought about the plastic sheath becoming a capacitor but of course it will. I have a Nano VNA and will use it to make some chokes. Thanks again for your help! 😄😄👍👍👍
@nickkendall3764 Жыл бұрын
Dam it mark.....strong words followed by other strong words some bleeps and then some less strong words.....now I need to rebuild my main choke as I'm useing 4 ft140 31 and 4 ft 140 43 toroids in a kind of binocular shape with 6 turns ish of my coax then directly into the radio I measured about 25 ish db down across hf and now I'm wondering if I split it in 2 and do 2 of the 31 mix and 2 of the 43 with 3 turns then repeat again so I have the 3 turns theory satisfied and the chokes In series theory also satisfied... dam you ye bleepus maximus
@SmittyHalibut Жыл бұрын
🤣🤣🤣 I’ll point out that you can MEASURE these things using the kit I sell now if you’d like, so you know for sure which configuration is better. I’d also request that you take notes, take pictures of the graphs, and at least write up your results, or do a video showing your results. Somehow, share it with the world. I will absolutely link that here and boost it. I haven’t done anything with binocular chokes, or mixing .. mixes.
@dreupen Жыл бұрын
I think this is a great idea. In reading the latest edition of QST, I enjoyed the article about a birdhouse LORA mesh network, and while there is no connection, I thought that a OHIS article in QST would be a great way to promote the OHIS concept to ARRL members.
@SmittyHalibut Жыл бұрын
Yep, been meaning to do that. Thank you for the reminder, I’ve created a ticket to remind me. github.com/open-headset-interconnect-standard/ohis/issues/11
@MoonMan133311 ай бұрын
Fantastic, and well thought-out! I have an old microphone that I’ve been wanting to use with a modern radio, and instead of creating a single interface, I think I might create an OHIS interface for each so I have future flexibility!
@SmittyHalibut11 ай бұрын
@@MoonMan1333 That's a great idea! I like it! Please let me know how it turns out for you.
@monolitesounds11 ай бұрын
Great work! Working with building automation and the standard BACNet as my referece to the Ohis😊 73 de sm5wyk ps. hamradioworkbench is the best podcast ot there😊
@donaldsmith3048 Жыл бұрын
How did the 2 clamp on with one coil work. It would use less coax and may give more blocking. Or I am thinking it would. 4 clamp ons should, in my mind do good on one coil. But I am not sure if I am thinking the right way.
@SmittyHalibut Жыл бұрын
It would almost certainly help, yes. The question is, which "costs more?" In dollars, ferrite is more expensive than cable and only increases the inductance linearly with the number of clamp-ons, where as adding turns of cable increases the inductance to the SQUARE of the number of turns. But if your source of cable is finite (eg: it's already in place and only so long), and you can afford to put more ferrites on it, then yes that sounds like the better option. To answer your direct question: I don't have data for what the two-clamps-on-one-loop looks like. I'll take this opportunity to point you to electronics.halibut.com/product/common-mode-current-choke-test-rig/ and ask you to post the results, though! 🙂
@tlebryk9 ай бұрын
Jim Brown (K9YC) had some useful graphs in A Ham's Guide to RFI and also in Understanding How Ferrites Can Prevent and Eliminate RF Interference. You should be able to search for those titles and his name.
@Sizzlik Жыл бұрын
Thanks very much! I was looking up what S11, S12, S21, S22 means and ended up bonking my head with formulas that explain scatter parameters. I know how and why inductors work but that Snn was new to me..easier then i thought..now it makes sense and i can use the values my vna spits out. Thanks alot.
@SmittyHalibut Жыл бұрын
I'm glad I could help! 🙂
@g0fvt Жыл бұрын
An excellent presentation, I have been experimenting with common mode chokes for a few years. Further down the comments you will see the observations I have made. Greater than 25dB is easily possible from 160m to 10m, I will retest mine on 6m but I suspect it will be fine there too. Spoiler alert, I no longer believe that winding them with coax is a good wideband solution...
@geekthesteve6215 Жыл бұрын
I searched for but couldn't find your other comment. I am interested in your findings and your choke design. Could you repost?
@g0fvt Жыл бұрын
@@geekthesteve6215 I couldn't find them either! I have done some experiments using twisted pairs pulled out of CAT5/6 cable, each pair has a characteristic impedance of nominally 100 ohms so two pairs fed in parallel retains a 50 ohm characteristic impedance. I have made many chokes wound with coaxial cable and always found the bandwidth disappointing. I have pictures and plots of this solution, nearly 40dB of attenuation at 7MHz...
@g0fvt Жыл бұрын
@@geekthesteve6215 This was my previous comment: Hi, I found similar, that interwinding capacitance appeared to be an issue with too many turns of coax on the core. Controversially perhaps my best wideband common mode chokes are wound with twisted pairs from CAT6 cable. Each twisted pair has a characteristic impedance of nominally 100ohms so effectively I have two in parallel to get to 50 ohms. I am getting much better bandwidth and very low insertion SWR.
@SmittyHalibut Жыл бұрын
@@g0fvt That's a really interesting idea. Do you know why the Cat6 results in wider bandwidth than coax?
@g0fvt Жыл бұрын
@@SmittyHalibut I believe that a major factor is the reduced capacitance between turns. I made a variety of common mode chokes wound with coax, but I found that putting too many turns on the cores caused the high frequency performance to deteriorate. The braid of even the small coaxes has a lot of cross section so adjacent closely spaced turns will couple significantly. The CAT5/6 conductors have a very small cross section, so should result in reduced capacitance between turns. Certainly the insertion SWR is surprisingly low and the common mode attenuation has a very broad characteristic. I have not tested my first example at beyond 100w carrier...so far...
@ploegmma Жыл бұрын
Very nice, thank you
@antennawhisperer-k7raw151 Жыл бұрын
Great work Mark! Now all you have to do to improve your test box is add a SPDT (3 position, center open) switch to the Port 0 wiring from the NanoVNA. Wire the "pole" pin as a short to ground on one "throw" of the switch and the same "pole" pin thru a precision 50 ohm resistor to ground on the other "throw" of the switch. Then add a SPST switch to bridge the center pins on the 2 output connectors for thru or "bypass" mode. VOILA,! You've now got a built-in calibrator too. Total of 3 switches: DPDT, SPDT (3-way), SPST.
@SmittyHalibut Жыл бұрын
That's not a bad idea. THe concern is, it doesn't take into account the connectors on the test side of the adapter. But, given all the other compromises we're doing, it's probably not really a lot worse. And, it still doesn't stop you from using your own SOL standards. I've put a ticket in my backlog to add that to the next revision of electronics.halibut.com/product/common-mode-current-choke-test-rig/
@SmittyHalibut6 ай бұрын
*psst* Keep an eye on electronics.halibut.com/ .. The next batch of CMCCs will have this feature on them. 🙂
@californiakayaker Жыл бұрын
I haven't seen the entire video so I apologize but thought I should say that TRX (a channel) has a video where he builds and measures the effectiveness of a common mode choke with a NanoVNA. I will come back when and if I see a measurement like he did. If not, go and see what he shows us.
@californiakayaker Жыл бұрын
I'm back. I like what I'm seeing very much. Its much more elegant to make a test device box. I think though, you were both doing the same test. That said, what did you think of his initial test of toroid material ?
@californiakayaker Жыл бұрын
That said, I'm only seeing you show poorly wound coax baluns, and nothing properly wound. So far anyway. I'm going to wind a tested design balun with a 43 mix and good enameled copper wire 1 to 1 and see if it does what others have measured. A coax balun is not the way to go. But, I do like your testing set up, and have both a regular nanoVNA and a V2.
@markcarpenter3600 Жыл бұрын
@@californiakayaker It depends on what problem you're trying to solve. If you have a perfect dipole antenna with identical shape and size no uneven obstructions in the near field a wire wound balun is better, I think we can all agree on that. A wire wound balun won't solve my problem in my mobile between 160m ~ 40m where I am attempting to capacitively couple with the earth. I need coax balums right behind the unun or it all goes to Hell real fast. You get the antenna perfectly tuned then start applying about 500 watts and it all falls right on its face, as the amplifier kicks out because it sees 60 watts coming back. 🤦 G3TXQ and K0BG discuss this on their websites.
@daienaa Жыл бұрын
So the swr meter in my cb radio shows all is good, no problems. So I went and bought me a external meter only to double check. I connected it, and what do I see... the meter says no good, swr way up there. Took a look at my radios meter and now it’s also showing a high swr all of a sudden. So I start to adjust the antenna a few times, checked if it did help and yes it did. My external meter shows a low swr. The radios swr agrees also, wow this is great! All I did was to plug the meter out and back with the antenna in the radio. But no, now after I disconnected and put the meter away, the radio says the swr is high! What the hell is going on? And how can I learn to fix this because I don’t have money now to go out and buy another meter. And since this is happening on my radio, I wouldn’t be able to make sure an older radio that I planned to buy would be sure. I could not even help if someone where to ask me to come with my swr meter and make sure there’s are not too high. What can I do to make the radios swr meter work together and show same good results like the did, until I discontent the external one. Radio is showing very high again.
@geekthesteve6215 Жыл бұрын
I am not an engineer but have been measuring antennas SWR for about 50 years and my guess is your coax length without the SWR meter and patch is resonant at 11 meters. Probably a multiple of 108 inches (a quarter wave at 11 meters or 27.255 mHz) times the velocity factor of the coax and an example would be .7 (velocity factor of your coax may be slightly different) times 108 inches, or a multiple of 75.6 inches, or 151.2 inches or 226.8 inches, etc.. Try leaving your patch cord in the line by replacing your SWR meter with a double female barrel connector and then check your SWR at the radio.
@daienaa Жыл бұрын
@@geekthesteve6215 Thank you, that sounds reasonable. Would a shorter coax cable from the swr meter to the radio help get reliable readings you think? It would be great if I could trust the swr meter if I ever should get a radio that has no built in swr meter or high swr protection.
@bill-20187 ай бұрын
Maybe a dry soldered joint in the new meter? Have you got r.f. chokes? I was given a supposedly non working MFJ160-10 tuner by a friend but I used it for two years, we went to Wales and still good but connecting it at home it no longer worked. Looking inside revealed nothing, it all looked perfect until I poked around and found a loose wire. It had been touching but not soldered. G4GHB.
@daienaa7 ай бұрын
@@bill-2018 Ohh this could be, because I bought it on amazon like budget version. The package of the cables says “uhf” so I was thinking it might be the reason, but then again a cable is just a cable, so I’m not sure 🤔
Пікірлер
Great presentation! Is there a way that a NANO VNA can output it's choke results in the magnitude of "Z" rather than dB?
I tried to make a 1:1 today but my toroid seem to be smaller than all those yt examples.
Thanks a lot for this video, now it is clearer for me, except that you speak fast and for a non-english-speaker it's not easy to understand but i've seen it two times and it's ok now !😁
That's a GREAT video explaining Common Mode Chokes - One thing, you never talk about power handling ability since these are usually used with TX as well as RX situations. The air core coax wound chokes would be limited only by power handling of coax, or close depending on how much capacitance affected power handling. The ferrite cores would be my concern - I think even the clipon ferrites would handle 100 watts, but when 1000 watts is involved it would require more?
A question just came up in my mind: If you use two ferrites in series, does the separation between the two matter? IOW, does the flux from each one couple with that of the other one? I think I'll start saving up for a VNA. Also, I'm curious about one other thing *(NOT* related to coax). If I buy a pre-made common mode choke, can I connect one of the sets of windings backwards and turn it into a *DIFFERENTIAL* mode choke? How would that compare with using two *separate* inductors (wound on *different* cores) for that purpose? _73 de AF6AS_
_Cal Poly?_ Which one? I graduated from _Cal Poly, Pomona_ in 1976 with a BSEE. _73 de AF6AS_
What would happen if one were to place the common mode choke in an iron or aluminum tube? For instance, if someone were to insert a linear common mode choke into the support mast itself to protect the coaxial cable from weather elements like UV rays? What are the potential impacts, and have you ever measured them?
Is Halibut Electronics going to be at Dayton this year?
BTW: engineers do not build e.g. bridges by a "trial and error" approach 😅
I'm new to the hobby . . I have made a choke balun which i want to use near my HF radio, It is made of 240 mix 43 toroid and RG-58, my question is: is the distance between the balun and HF rig critical ? jumper i made will give me 8 inches distance b/w choke and radio
These are the answers about common mode that I have been looking for , for a long time. great lesson, thank you
I'm glad it helped. 🙂
Top presentation, graphics and explanation! I am yet to play with my VNA and just got some 31 mix torroids for this exact purpose. I have not seen anything like that test box but would like to build one. I have bookmarked the video for playlist to build. Perfect timing, thank you!👍🤠🇦🇺73 de VK1DON
Funny you should mention wanting to build a CMCC Test Rig. When I recorded this, I hadn’t yet started my own company. I now sell those kits. electronics.halibut.com/
Very good presentation and treatise of one of the most prevalent ham station basic problems....
Thank you. :-)
Forgive my late input . I note in a few of the comments that many would love to see a comparison against a Coax bottle type Choke and what the attenuation figures come out like . . Great video by the way . Well done 73. Ron G4DIY
Thanks for the positive feedback! I'm not sure what design you mean by "Coax bottle type choke". A quick google search turned up a design where you wrap coax around a pill bottle? Is that what you mean? If so, that's just an air-core choke. The bottle is only a form to wrap the coax around, but doesn't appreciably impact the magnetic permeability of the choke. If you mean some other design, please point me to a page or article describing what you mean.
@@SmittyHalibut hi there again. Well my “bottle type “ is literally a plastic bottle about 8 inches high and about 4 inch diameter . I have coiled Rg 213 Coax around it with about 20 turns . So its a coaxial choke effectively.
@@ronbennett5591 Ok, yeah. So it's an air-core choke. I've gotten feedback elsewhere in this comments section that I never gave a properly-wound air-core choke a fair shake, and that's true, really. I need to make an update to this video with my CMCC Test Rig kit instead of the hand-built test rig in this video; when I do that, I'll give an air-wound choke a proper test.
Hi, I find that a 1:1 choke will degrade my reception by 1-2 S. Is this ok? I have a choke on a toroid with 121 turns of coax
121 turns! That seems excessive. Depending on what coax that is, you're probably just seeing the loss of so much added coax in your feedline. If that was supposed to be 12 turns, that's much more reasonable and at that point, I suspect something is wrong with the choke. A properly functioning choke should have zero impact on the normal reception of your antenna system, except the added loss of the additional feed line in the choke itself. But that should be around 1dB for moderate coax, and less than that for good coax. It'll be WAY less than 1 to 2 S units (an S unit is 6dB, so that's 6 to 12dB!)
Of course 12 threads. RG58 on FT240-43 toroid. Attenuation according to VNA 25-35db. There's nothing wrong with that. On ft8 lower report. When SSB calling kiwisdr, I can hear myself much more faintly. I don't understand why that is. Where can I go wrong? @@SmittyHalibut
@@miranovak8098 attenuation, using my test rig to measure the common mode of the choke? Or just connected directly to the VNA? If you’re using the adapter described in the video (that I sell now, electronics.halibut.com) then 25dB common mode loss is good, but that’s not what you need to measure for reception loss. Connect your choke directly to the VNA, no adapter. And measure the S21 LOGMAG on that. That should be 0dB loss, or very close to it. If it’s higher than 0dB, something is very wrong with the choke.
The coax might be damaged by the winding process ?
It might be, depending on the cable. Thats why I use RG316, which has a very small minimum bend radius, for winding on FT140 cores. Larger coax on larger cores, you definitely should not abuse the minimum bend radius. It’s possible that’s what’s happening here on @miranovak8098 ‘s choke.
Excellent explanation and test work Mark. As another RF guy I am troubled by 2 things. One at 09:20, how can CM noise get inside a shielded radio when applied between coax shield and transceiver "ground"? I suspect all CM noise entry is either via poor coax or transceiver shielding. Two at 22:03 is the assumption that a CM choke should be X times the cable Zo. I doubt that the surge impedance on the outside of the coax is also 50 Ohms. Anybody wiser?
1: you’re probably right that RF gets in on bad coax too. Heck, it’ll get in on the antenna itself! But any non-perfect ground will also put that noise into the receiver. 2: The goal is to make the common mode impedance as high as possible at the target frequency. Common wisdom as proposed by people smarter than me is “about 1000 ohms.” That’s about 20x a 50 ohm system … and I think I’m realizing I did my dB math wrong in the video. That’s 20x impedance (linear with power), not 20x voltage (square with power). So it’s only 13dB, not 26dB. If I’m right, all the numbers I gave in the video are twice as good as they “need” to be. Huh. Well, we have some mighty fine CMCCs out there I guess.
@@SmittyHalibut Yup I agree with the math. Just the relation to 50 Ohms which is the internal cable Z not the outside "third wire". No matter, we need Z as high as possible, in most cases with a good Rloss to gobble up energy. As far as RX CM I think it is an "all cables" sneak in (line cord, USB, LAN...). CM chokes DO help. But as for TX induced RF chokes should be at a voltage maxima on the line where ever that it is. PS It is amazing how far the ham community has come in understanding lines, VNAs etc. Cheers!
I took issue with the description of a coax as a differential cable early on in the talk (around 4 minutes). Signal Integrity engineers refer to them as single ended for a reason or two - a differential cable, for example requires at least 4 vna ports set into 2 logical port groups; and the shield is not the return conductor, it is a shield. It serves the same purpose as the shield over a twisted pair like in an ethernet cable, which is a true differential system. One more comment is that shields of coax are almost always tied to the chassis ground on both sides, not the signaling elements of a transceiver so there is no push-pull of currents. Any differential currents created are simply inductive coupling between the center conductor and the shield. That all said, I love the data collected on the experimental chokes the nanoVNA plots. I wish we could have seen data for 2 chokes placed on a single gordian knot to see how adding chokes improved the common mode rejection also.
I just re-watched that section to make sure I was thinking about the right thing. You are absolutely correct that there is a world of difference between a Single Ended signal (like on coax) and a Balanced signal (like on twin lead, or twisted pair). But that's more about voltages, not currents.. (Yes, voltages which then drive currents though impedances, yes, so it's not entirely NOT about current... See below...) But even a Single Ended signal will have opposite and equal current flows on the coax. My mistake was referring to those currents as "balanced", little b, the adjective. They are not Balanced, big B, the proper noun describing the signal type. That's why it's called Differential Mode for currents, because that's different than Balanced for voltages. The push-pull of currents part, again, you are correct. That's the impact of a Balanced (big B) signal on the currents that we talked about earlier. But that still doesn't mean that there isn't an equal and opposite current flow on the feed line. If there's no other return path for current, it HAS go to on the feedline. And even if there is another return path for current, like you said, it will induce the return current in the coax and probably prefer that path over the other (assuming your coax is well connected and low impedance compared to the alternate path.) So, you're not wrong in any of your response. But I think those points don't really impact the description of the examples presented.
FANTASTIC tutorial. 30+ year BSEE and Electromagnetic major here. You know your subject and can present it well. Thank you for all the work put into this.
Thank you! I appreciate the kind words. :-)
I too have done some research and testing to determine the optimum ferrite materials and number of turns to get the most out of my RFI choke filters. I based my conclusions on ferrite manufacturers equations and my personal tests using signal generator, oscilloscope and nanoVNA to sweep the entire HF band (e.g. building a combined differential and common mode filter for the output of a home-brew DC switching power supply for my shack). I too found that, for a snap-on ferrite, 0.5 inch hole, type 31, 3 turns was optimal before capacitive coupling between turns reduced effectiveness. But for an FT-240-31 I think 5 to 7 was optimal, according to manufacturer's equations and testing (this was 3 years ago so I don't quite recall exactly). However, I also built a 1:1 current balun for use as a wire dipole feed point and I put 11 turns (16 AWG PTFE insulated wire, split and wound in two direction) on that one, and it tested extremely well, -35 dB attenuation across most of the HF band. So it seems the geometry of the toroid makes a big difference in terms of how many turns is optimal. And your tests also showed better braud-band attenuation with the 13 turns around a FT-140. Do you have a general explanation for this? Why does the capacitive coupling add up so much with the snap-ons?
Its more about the turns of cable than the ferrite material. When on a torroid, the turns are spread out, more space between windings. When wrapped in a "Gordian knot", they're immediately adjacent to each other, maximizing the capacitance between turns.
I never bothered with chokes at one time but decided to try ferrite rings a few years ago. I looked at the G3TXQ site for information which rings to use and how many turns to use for a particular range of frequencies. No dipole of mine has ever been in the clear and my inverted vee is squashed into a 25' x 12' garden but, hey, it works! The first was on my 60m inverted vee at the aerial. It didn't seem to do much to stop r.f. getting down the coax and back into the shack. I then tried it inside the shack and it did stop r.f. getting back. I put two more at the aerial ends of my two coax cables to my five 20m to 10m dipoles in the attic. I did the same with these and put them in the shack. These are now in the shack as well. I came to the conclusion that r.f. was getting onto the cable after the choke so they might be better lower down the coax. If you think how long a wavelength is it can easily get on the coax below the choke. I've seen two aerial manufacturers say these two different things about where to put them. I also thought that two chokes, one at the aerial and one close to the tx might be a good idea. G4GHB.
Another benefit of the OHIS is user experience and ease of use. How many times have you purchased a headset or mic and didn't get the right adapter, or had to build your own adapter? How much time have you poured over pinout diagrams or relied on vague descriptions from some log forgotten blog post? Did you read the pinout backwards? Oops. Time to rewire or buy another connector. The user experience improvement benefits both device and radio makers.
16:00 - outer conductors of the two NanoVNA ports (at least on the old 1.5G one, the one made out of three SA612A mixers) are shorted through the device's common ground, just FYI
True. That would make the plane of testing right at the edge of the VNA, including the cables between the VNA and the test rig, which is ... less than ideal... 🙂
Excellent video brother
Thank you. Very nicely made and easy to understand.
Dude, you need to make more videos ! Good Job !
:-) Thank you.
What if the coax has two shields, one inner foil and an outer braid?? Does that mean 5 currents?? How to wire up an RF choke with toroid ferrite??????
If the foil and braid are touching, then no, consider that a single shield. If there’s a layer of insulation between the inner and outer shield, then you have a special coax that’s designed specifically for keeping differential mode and common mode currents separate. I’m not an expert on these, but I think the goal is to ground the outer shield to the chassis at the transmitter and leave it disconnected at the antenna. It’s basically a shield for the feedline. Then the inner shield can be connected directly to the transmitter amplifier ground reference (not the chassis), and the antenna. It’s a more complex transmitter arrangement. If you don’t have that, then just connect both shields to the transmitter, and only the inner shield at the antenna.
I think this is a good idea and not just for hams. There are plenty of devices with unusual audio interfaces outside of ham radio. Not as common but they're out there. I'm skeptical of the idea that manufacturers will put this interface in radios because my understanding is they make a big chunk of money off of selling accessories and if they have to compete for accessory sales they will be financially up a creek.
I've spoken with a few manufacturers and I categorize their response as Optimistic Skepticism: "That's a really great idea! I don't think it'll ever happen." :-/ I actually think it's not that bleak. Your point is totally valid, but OHIS doesn't have to REPLACE their existing ecosystem. I'm not asking the big three to do away with their GX16 mic connectors, but to add an OHIS port next to it, or maybe on the back of the radio. They already have the "Accessory" port which duplicates the audio in and out and PTT, so I know they CAN do it. The trick is convincing them that it's WORTH doing with a standard. And the way to do that is to get traction on that standard. So that's what I'm trying now.
Very cool...and timely. It would be nice to add the CW Keying Line...but all out of pins, (maybe in CW mode the PTT line becomes the keying line). My interest is in being able to easily SWITCH between radios in my collection of rigs. I've just completed a modular desk project that allows me to physically arrange the equipment for ease of access. This standard helps tremendously with the switching project, even though my rigs' manufacture dates span decades. I look at the "Adapter Project" as a retrofit solution for legacy equipment. If all radio manufacturers, starting tomorrow, were to equip their radios, with OHIS ports and the headset, mic PTT switch manufacturers released their products with OHIS plugs, obviously no adapters would be needed; hence my view of the current status as a retrofit of legacy equipment. Various attempts have been made to produce products for RIG selection, but none that I've seen have taken the 40,000 foot view that you have...great work!
Thank you for the kind words! 🙂 This video is intended as a generic standards advocacy video and doesn't touch on the devices my company Halibut Electronics makes. I'm currently selling adapters (pre-sale, delivery in October 2023), and am working on two "Consoles" to go between the radio and the user. The first is the Contesting Console (two users, one radio), the second is the Station Console, which is what you're describing: multiple radios, one user. It's expected for release sometime in the first half of 2024. And, yes. Ideally, manufacturers would adopt OHIS and start putting OHIS ports on their gear natively, no adapters necessary. But I acknowledge that they are unlikely to do that until there's some traction with the standard. Adapters are the bridge technology to get us there.
Good idea but how about a bluetooth interface with it too.
The standard is just the electrical middle part. The devices that implement that standard is where the Bluetooth would be. There's nothing stopping anyone from making a User adapter that connects to a Bluetooth headset instead of a cabled headset. Or a Radio adapter that LOOKS LIKE a Bluetooth headset and presents an OHIS Radio port. I'm not sure how standard the Bluetooth PTT stuff is though, how difficult that would be to implement. I'm currently concentrating on wired analog solutions and haven't really researched the Bluetooth stuff yet.
Nice presentation and it makes sense to test any balun before use to actually know what you are getting. Thank you and now I need to test.
I know I'm kinda late (apparently not getting notifications for many of the comments on this video!), but I will point you to electronics.halibut.com/product/common-mode-current-choke-test-rig/ 🙂
Excellent thank you very much
Thanks for the video. As I was watching I was wandering about influences of possible phase shifts in the device. The influence on the working of the common mode choke. Signal coming in the choke (on one side) and signal comming in (on the opposite side and from the opposite direction) may have some phase shift. The load is probably not pure resistive....
Are you talking about the Differential Mode response, meaning how transparent it looks to the signals flowing through it? Or the Common Mode response, meaning how the phase affects the resistive/reactive balance of the impedance it imposes? If the former, the Differential Mode view, by definition Differential Mode currents sum to zero through the inductor, so there is no impact at all. When I=0, it doesn't matter what the j component of X is because it will be multiplied by 0 to get your V vector. "What if phase differences result in I!=0?" Then those differences would become Common Mode. By definition. If the latter, the Common Mode view, then yes you're absolutely right. The impedance imposed by a Common Mode Current Choke is not purely resistive across the whole band of interest. It's an RLC complex circuit. An IDEAL choke would be all R and very little LC over the whole band of interest, but that's nearly impossible. In the video I show highly resonant chokes with a very deep attenuation "peak" (shown as a "valley" on the graph because it's a negative number). In those cases, if you measured the Complex Impedance of the CMCC, you would see a high R/low X at that peak, because that's the resonant point of the choke, and resonance at the frequency happens when f*L and f*C are equal but opposite, which cancels them out and leaves you with nothing but R. But outside that peak, the response becomes very reactive.
Electrically speaking, what's the difference between balanced and unbalanced?
Balanced means the voltages go up and down relative to ground on BOTH wires, with the same signal but inverse of each other. The average voltage is always 0, always ground. This is what you have on twin-lead feedlines like ladder line, or XLR mic cables. Unbalanced means one wire is ground, a fixed voltage, and the other wire goes up and down relative to the ground reference. This is what you have with coax like UHF/BNC/N connectors, or RCA audio cables. There are some special cases that I’ll ignore here (like “pseudo balanced,” and phono (as in record players) signals which can be treated as balanced, despite the use of RCA connectors.)
Balanced and unbalanced has to do with the voltages. This is not to be confused with differential mode and common mode, which has to do with currents. Differential mode currents are when the current flowing in each wire of your transmission line are exactly balanced. The same amount of current flowing in both directions. The sum of the currents is zero. Common mode current is any difference between the currents in the transmission line. If the sum of currents is NOT zero, the bit that is not balanced between the two wires is the common mode. For example: if there’s a transmission line, two wires, whether balanced or unbalanced, and one wire has 2A flowing one direction and the other wire has 3A flowing the other direction, then there is 2A of differential mode current and 1A of common mode current.
@@SmittyHalibut so you're saying that the voltages go up and down relative to ground in both wires. So if I power my transceiver with a center tap transformer so that the ground is between the pl 259 shield and the other side, the shield and the center conductor will be equal voltages 180° apart and therefore balanced? How does that change the operation of my transmission system in the long run? What does it matter where my reference ground is electrically?
@@BusDriverRFI Don't do anything to the AC power input on your radio. That will cause all kinds of damage. A given transmission line is either balanced or unbalanced. Coax is inherently unbalanced, twin-lead is inherently balanced. If you want to convert from one to the other, you use a (real) Balun (not the things a lot of people claim are baluns.) There are a few reasons one would choose a balanced transmission line over unbalanced. Balanced transmission lines have less loss than coax; for VERY high powered systems (100kW and more), coax becomes large copper pipe and becomes incredibly expensive, where balanced transmission lines can still just be large gauge wire. For hams, a well deployed balanced signal can also be better at eliminating common mode noise than coax. This can be useful on receive. The downsides to a balanced signal is that its fields extend past the boundary of the cable itself, whereas coax is entirely contained inside the cable. This means you have to be very careful how you deploy balanced cable: If you put anything close to the cable that interacts with the E and M fields (eg: running it close to a metallic tower), it will impact the signal. So you have to space it away from near by stuff, including other balanced transmission lines. You don't have to do this with coax: You can tie it immediately to the tower, next to other coax runs, power cables, whatever. It doesn't matter because all the RF is contained entirely inside the shield. Weighing these pros and cons, most hams are running low enough power and good enough coax that the disadvantages of balanced feed lines outweigh the advantages. So most of us use coax. But you see balanced feed lines a lot more in much larger installations.
@@SmittyHalibut seems strange that a 1:1 could cause all kinds of damage. I wasn't going to do that anyway because I don't want high voltage on my radio case. It was a hypothetical question and not a practical question as to determining whether the "unbalanced" line would be considered "balanced" if it was fed with the "balanced voltage" input. Seems logical that since we are talking about the voltage being balanced, the thing keeping coax from being balanced is the input biasing.
built one as well, as per your istructions (the version with the switch). works as a charm! maaany thanks!!!
Yay! I'm glad to hear it! 🙂
You need to relearn your theory. An inductor does NOT stop the flow of AC or RF current no matter what inductive reactance present. What stops and attenuates common mode is resistive parallel resistance that dissipates the common mode. An inductor does not consume power it just changes it's phase. Cores create this resistance within the core characteristics.
Thanks for the constructive input. I‘m sure Marc appreciates it 👍🏼 It helped me understand it better.
Alright, you just put all the pieces of the puzzle together. Fantastic work and presentation. Following.. Thank you so much!
I’m glad I could help. :-)
Great talk. Thinking about getting my ham license, but I think I’d be in the “mostly building, not operating” group as well. What are POTA and SOTA?
“OTA” usually means “On The Air” so it’s just a matter of the first letter(s). POTA is Parks, and SOTA is Summits. Both their websites can be found by searching. (Read: I don’t remember the URLs off hand. :-)
First of all, nice video, one of the best I've seen on building a CM choke. Only one minor comment: "Building something and trying it" is NOT really an "engineering approach". It is actually an "experimental" approach. As an engineer for 43 years, I found that taking an "experimental approach" ended up taking up a lot more time in the "development phase" of a product than working the design out mathematically before laying any lines down on a drawing. Having said that, I frequently approach my amateur radio projects as experimental in nature simply because I like building a lot more than I like math. In amateur radio I am not bound by schedules, budgets, difficult test requirements, etc, so I can enjoy the build to "see what I end up with". So, this is not meant to be a negative comment about your video. I found your explanations were clear and accurate with nice visual aids, and more importantly easier to understand than wading through the math. Good overview on setting up and using a VNA, too. --Mark, KE6BB 👍
That’s a fair point. I think what I was trying to say was “practical” vs “theoretical.” To me, that’s the difference between engineering and science. Engineering is more applied, science is more conceptual. But you’re right, “experimental” is an even better term for what I’m doing here. Thanks for the feedback! :-)
Awesome stuff! When you talked about calculating or experimenting with Gordian Knots to make a choke for a specific band, I had to comment because I've done exactly that. I fly paramotors, wanted to build an antenna for GMRS (462 MHz) out of a chunk of RG316 with half of the coax sheath removed, then string it up one of the glider lines. 2 problems: 1) "Center/core fed vertical" doesn't resonate well on any frequency. Experimenting showed that the angle between the two legs needs to be around 30° (aIrc) for resonance, and 2) Even if I got it resonant, Instill needed to decouple the antenna from the feed line, otherwise the radio body, the hand holding it, any metal or human near the coax would cause wild swings in the SWR. So I added a Gordian Knot, and experimented until I reach both resonance and decoupled the antenna from the feed line. In my case there was 2 loops at around 6cm diameter. Location of the knot along the coax was also critical. Couple of us flew those antennas for a while and they worked well but wore out quickly. Next version will be with more flexible coax, and the knot up higher on the line so it won't get beat up as badly during handling. Also trying to figure out how to do multibands ...lol
That's awesome! (Sorry for the late reply; not sure why I didn't get a notification for this one.) Gordian knots can work well for mono-band operations, if you tune them. And a rig like described here can help you do that. But they are inherently mono-band.
Neat work, you do need to have an understanding of the basic physics, but really, what better way than showing by practicality what effect any changes would have on your desired output. I have nothing to do with ham radios but even i understood the whole concept as presented. Well done.
Thank you for the kind words. 🙂 And, if you ever decide you want to get your ham radio license, KZread (and the Internet as a whole) has a whole lot of resources to make that happen. Just let me/us know, and we'll point you in the right direction. Cheers!
Thanks for this video, as a returner to the hobby after nearly 40 yrs, it was very useful to me. Forgive me if this is a dumb question but please would you confirm that when you say "outside" you mean outside edge of the shield and not the outside plastic sheath of the coax? I ask this because I know you can get RF burns from the very outside of the plastic sheath of a coax. Thanks again.
Not a dumb question at all! The currents are traveling on the shield, that is true. But RF can capacitively couple through the insulation into your skin. If the currents are high enough, then yes you might get burned (more likely a tingle) from touching the coax. Now, that’s a REALLY BAD common mode current. If that’s happening, something is seriously wrong with the antenna or feed system. Under normal circumstances, with normal levels of reflected common mode current, it’s very unlikely you’ll get an RF burn by touching insulated coax. But once that current hits the metal chassis of the radio, or the shielded-not-insulated microphone that’s in your hand, you’re much more likely to feel even small to moderate amounts of current. Get thee a CMCC post haste! :-)
@@SmittyHalibut Thanks so much for your detailed reply, it all makes sense now. I had not thought about the plastic sheath becoming a capacitor but of course it will. I have a Nano VNA and will use it to make some chokes. Thanks again for your help! 😄😄👍👍👍
Dam it mark.....strong words followed by other strong words some bleeps and then some less strong words.....now I need to rebuild my main choke as I'm useing 4 ft140 31 and 4 ft 140 43 toroids in a kind of binocular shape with 6 turns ish of my coax then directly into the radio I measured about 25 ish db down across hf and now I'm wondering if I split it in 2 and do 2 of the 31 mix and 2 of the 43 with 3 turns then repeat again so I have the 3 turns theory satisfied and the chokes In series theory also satisfied... dam you ye bleepus maximus
🤣🤣🤣 I’ll point out that you can MEASURE these things using the kit I sell now if you’d like, so you know for sure which configuration is better. I’d also request that you take notes, take pictures of the graphs, and at least write up your results, or do a video showing your results. Somehow, share it with the world. I will absolutely link that here and boost it. I haven’t done anything with binocular chokes, or mixing .. mixes.
I think this is a great idea. In reading the latest edition of QST, I enjoyed the article about a birdhouse LORA mesh network, and while there is no connection, I thought that a OHIS article in QST would be a great way to promote the OHIS concept to ARRL members.
Yep, been meaning to do that. Thank you for the reminder, I’ve created a ticket to remind me. github.com/open-headset-interconnect-standard/ohis/issues/11
Fantastic, and well thought-out! I have an old microphone that I’ve been wanting to use with a modern radio, and instead of creating a single interface, I think I might create an OHIS interface for each so I have future flexibility!
@@MoonMan1333 That's a great idea! I like it! Please let me know how it turns out for you.
Great work! Working with building automation and the standard BACNet as my referece to the Ohis😊 73 de sm5wyk ps. hamradioworkbench is the best podcast ot there😊
How did the 2 clamp on with one coil work. It would use less coax and may give more blocking. Or I am thinking it would. 4 clamp ons should, in my mind do good on one coil. But I am not sure if I am thinking the right way.
It would almost certainly help, yes. The question is, which "costs more?" In dollars, ferrite is more expensive than cable and only increases the inductance linearly with the number of clamp-ons, where as adding turns of cable increases the inductance to the SQUARE of the number of turns. But if your source of cable is finite (eg: it's already in place and only so long), and you can afford to put more ferrites on it, then yes that sounds like the better option. To answer your direct question: I don't have data for what the two-clamps-on-one-loop looks like. I'll take this opportunity to point you to electronics.halibut.com/product/common-mode-current-choke-test-rig/ and ask you to post the results, though! 🙂
Jim Brown (K9YC) had some useful graphs in A Ham's Guide to RFI and also in Understanding How Ferrites Can Prevent and Eliminate RF Interference. You should be able to search for those titles and his name.
Thanks very much! I was looking up what S11, S12, S21, S22 means and ended up bonking my head with formulas that explain scatter parameters. I know how and why inductors work but that Snn was new to me..easier then i thought..now it makes sense and i can use the values my vna spits out. Thanks alot.
I'm glad I could help! 🙂
An excellent presentation, I have been experimenting with common mode chokes for a few years. Further down the comments you will see the observations I have made. Greater than 25dB is easily possible from 160m to 10m, I will retest mine on 6m but I suspect it will be fine there too. Spoiler alert, I no longer believe that winding them with coax is a good wideband solution...
I searched for but couldn't find your other comment. I am interested in your findings and your choke design. Could you repost?
@@geekthesteve6215 I couldn't find them either! I have done some experiments using twisted pairs pulled out of CAT5/6 cable, each pair has a characteristic impedance of nominally 100 ohms so two pairs fed in parallel retains a 50 ohm characteristic impedance. I have made many chokes wound with coaxial cable and always found the bandwidth disappointing. I have pictures and plots of this solution, nearly 40dB of attenuation at 7MHz...
@@geekthesteve6215 This was my previous comment: Hi, I found similar, that interwinding capacitance appeared to be an issue with too many turns of coax on the core. Controversially perhaps my best wideband common mode chokes are wound with twisted pairs from CAT6 cable. Each twisted pair has a characteristic impedance of nominally 100ohms so effectively I have two in parallel to get to 50 ohms. I am getting much better bandwidth and very low insertion SWR.
@@g0fvt That's a really interesting idea. Do you know why the Cat6 results in wider bandwidth than coax?
@@SmittyHalibut I believe that a major factor is the reduced capacitance between turns. I made a variety of common mode chokes wound with coax, but I found that putting too many turns on the cores caused the high frequency performance to deteriorate. The braid of even the small coaxes has a lot of cross section so adjacent closely spaced turns will couple significantly. The CAT5/6 conductors have a very small cross section, so should result in reduced capacitance between turns. Certainly the insertion SWR is surprisingly low and the common mode attenuation has a very broad characteristic. I have not tested my first example at beyond 100w carrier...so far...
Very nice, thank you
Great work Mark! Now all you have to do to improve your test box is add a SPDT (3 position, center open) switch to the Port 0 wiring from the NanoVNA. Wire the "pole" pin as a short to ground on one "throw" of the switch and the same "pole" pin thru a precision 50 ohm resistor to ground on the other "throw" of the switch. Then add a SPST switch to bridge the center pins on the 2 output connectors for thru or "bypass" mode. VOILA,! You've now got a built-in calibrator too. Total of 3 switches: DPDT, SPDT (3-way), SPST.
That's not a bad idea. THe concern is, it doesn't take into account the connectors on the test side of the adapter. But, given all the other compromises we're doing, it's probably not really a lot worse. And, it still doesn't stop you from using your own SOL standards. I've put a ticket in my backlog to add that to the next revision of electronics.halibut.com/product/common-mode-current-choke-test-rig/
*psst* Keep an eye on electronics.halibut.com/ .. The next batch of CMCCs will have this feature on them. 🙂
I haven't seen the entire video so I apologize but thought I should say that TRX (a channel) has a video where he builds and measures the effectiveness of a common mode choke with a NanoVNA. I will come back when and if I see a measurement like he did. If not, go and see what he shows us.
I'm back. I like what I'm seeing very much. Its much more elegant to make a test device box. I think though, you were both doing the same test. That said, what did you think of his initial test of toroid material ?
That said, I'm only seeing you show poorly wound coax baluns, and nothing properly wound. So far anyway. I'm going to wind a tested design balun with a 43 mix and good enameled copper wire 1 to 1 and see if it does what others have measured. A coax balun is not the way to go. But, I do like your testing set up, and have both a regular nanoVNA and a V2.
@@californiakayaker It depends on what problem you're trying to solve. If you have a perfect dipole antenna with identical shape and size no uneven obstructions in the near field a wire wound balun is better, I think we can all agree on that. A wire wound balun won't solve my problem in my mobile between 160m ~ 40m where I am attempting to capacitively couple with the earth. I need coax balums right behind the unun or it all goes to Hell real fast. You get the antenna perfectly tuned then start applying about 500 watts and it all falls right on its face, as the amplifier kicks out because it sees 60 watts coming back. 🤦 G3TXQ and K0BG discuss this on their websites.
So the swr meter in my cb radio shows all is good, no problems. So I went and bought me a external meter only to double check. I connected it, and what do I see... the meter says no good, swr way up there. Took a look at my radios meter and now it’s also showing a high swr all of a sudden. So I start to adjust the antenna a few times, checked if it did help and yes it did. My external meter shows a low swr. The radios swr agrees also, wow this is great! All I did was to plug the meter out and back with the antenna in the radio. But no, now after I disconnected and put the meter away, the radio says the swr is high! What the hell is going on? And how can I learn to fix this because I don’t have money now to go out and buy another meter. And since this is happening on my radio, I wouldn’t be able to make sure an older radio that I planned to buy would be sure. I could not even help if someone where to ask me to come with my swr meter and make sure there’s are not too high. What can I do to make the radios swr meter work together and show same good results like the did, until I discontent the external one. Radio is showing very high again.
I am not an engineer but have been measuring antennas SWR for about 50 years and my guess is your coax length without the SWR meter and patch is resonant at 11 meters. Probably a multiple of 108 inches (a quarter wave at 11 meters or 27.255 mHz) times the velocity factor of the coax and an example would be .7 (velocity factor of your coax may be slightly different) times 108 inches, or a multiple of 75.6 inches, or 151.2 inches or 226.8 inches, etc.. Try leaving your patch cord in the line by replacing your SWR meter with a double female barrel connector and then check your SWR at the radio.
@@geekthesteve6215 Thank you, that sounds reasonable. Would a shorter coax cable from the swr meter to the radio help get reliable readings you think? It would be great if I could trust the swr meter if I ever should get a radio that has no built in swr meter or high swr protection.
Maybe a dry soldered joint in the new meter? Have you got r.f. chokes? I was given a supposedly non working MFJ160-10 tuner by a friend but I used it for two years, we went to Wales and still good but connecting it at home it no longer worked. Looking inside revealed nothing, it all looked perfect until I poked around and found a loose wire. It had been touching but not soldered. G4GHB.
@@bill-2018 Ohh this could be, because I bought it on amazon like budget version. The package of the cables says “uhf” so I was thinking it might be the reason, but then again a cable is just a cable, so I’m not sure 🤔