Excellent! Good explanation and demo. Looks like a nice analyzer. Hope the 102 is working well.

Thanks. Good explanations. Like your rig, I started out with an SB - 101 back in ‘76.

@MegawattKS

3 жыл бұрын

Thanks. The SB-101 (or 102) is awesome. When I was in high-school, I could only experience those by looking at them in catalogs. But a few years ago, I finally bought that one on Ebay and did some restoration. It had some challenging issues, but I've finally gotten them worked out. The VFO is just insanely smooth and stable. And I think I've got the sensitivity up to close to original. The mic input seems to be very insensitive, but I believe that's just because my dynamic is lower output than those used back in the 70s ? 73's

The concept from Heath was an affordable Collins KWM-2. If you looked inside both rigs you immediately see what I mean. Collins approach involved a PTO with each band tweaked by slug tuned circuits. It’s s great design. Regarding Microphones. I used a Motorola Base station mic. at my station...same vintage as the transceiver, an Astatic D-104 could be an OK choice too, my key was a surplus J-38 that used to sell for around a dollar. Started with a 40m inverted version then a tower and tri-band beam. It was a good station. It’s all changed now but the radio is still a good one.

@MegawattKS

3 жыл бұрын

I had an Eico 7-drifty-3 (aka 753). It taught me the value of a good VFO via the school of hard knocks :-) I think maybe I"ll eventually get a D-104 for the 102. I had a D104 with the Eico and had good signal reports (while drifting off frequency ;-) Your antennas sound great too. I just had a 40m dipole that was way too close to the ground. But I was able to work S.America a few times (easy pickens of course).

Amazing for nano VNA

Return loss is my focus, not swr. 10dB return loss, is pretty good, about a 1.6:1 swr.

@MegawattKS

3 жыл бұрын

Agreed. S11 is much more direct. For -10 dB S11 (10 dB return loss), I actually compute a reflection coefficient of 0.316 which gave me an SWR of 1.93. Regardless - still plenty good, and 10 dB RL or better is the common goal as you noted. I wish I would have mentioned that in the video. I just said "one division down" which isn't always the case depending on how many dB per division it is set to. Thanks for noting that, and for watching :-)

Thank you for your videos 🙏. I don't yet own a nano vna. (But I've ordered one online). Ideally I would also like to measure the suitability of junk box inductor cores to be used at specific frequencies. I'm thinking if I use a core to wind a 1:1 transformer and then connect the vna to primary and a known 50ohm to secondary, if the core is lossless I should just see the 50 ohm? Any losses should manifest as additional resistance (?) . Or is there a better way. I watched an excellent video on inductors by applied science, but his method requires a $40K scope !!!!!

@MegawattKS

6 ай бұрын

It's worth a look. Unfortunately however, losses in RF transformers (and baluns) can lead us astray. For example, a very lossy transmission line used to feed an antenna can make the antenna look like a good match even if it isn't. This is because the outbound signal from the VNA is attenuated by the losses, and even if the antenna has high reflection (high VSWR), the reflected signal (from a not-great antenna) will again be attenuated on the way back. So the VNA sees the return signal much less than the outbound one and reads as a good match across a broadband of frequencies. Something similar could happen with the balun. BUT - an easy way to check the balun (if it's supposed to be for 50 Ohm source and term, as I think you're saying) is to use S21 mode. If the balun is good, you should see 0 to -2 dB or so for S21 when port one is connected to one side and port 2 to the other. S21 in this case is directly measuring losses :-) Check the S21 cal to make sure it reads a nice 0'ish dB before the test though (using one of the short SMA to SMA cables that comes with it. [NOTE: this doesn't as well for 75 Ohm, or other non-50Ohm tests, since S21 is defined w/r/t 50 Ohm sources and loads...]

@coffeecuppepsi

6 ай бұрын

@@MegawattKS thank you very much for the detailed answer 😀

I think perhaps you have the scattering parameters improperly identified. S11 is the input RL of the DUT S21 is the transmission loss between the input and output. S12 is the reflected energy from the output to the input. S22 is the output port return loss of the DUT.

@MegawattKS

3 жыл бұрын

Hi Jerry. Thanks. Can you specify where in the video? I definitely might have misspoke, or I might have been unclear, like when I said a large dip in the S11 plot was a good SWR. In reviewing it, I also noticed at time 3:52 I equated S11 to RL - which is qualitatively correct. But to be precise that's a little incorrect, as S11 is actually the return-gain and is the negative of RL (when in dB). S11 = Vref/Vfwd with port-2 terminated - or, as in this case, port2 doesn't exist for the measurement since the antenna is a one-port DUT. And S11 in dB is 20 log of that. SWR is of course a different animal entirely (It's (1+|S11|)/(1-|S11|)). That might have been confusing. What I was trying to say is that the SWR at the 7 MHz dip is also a good value. The first bullet on the powerpoint slide near the end does say S21. Sorry about that. No relationship to SWR for that...

@bkj242

3 жыл бұрын

@@MegawattKS S11 is the input RL in dB and NOTHING to do with SWR. SWR is a completely separate measurement involving other components. When you refer to a”dip” in the Smith Chart I haven’t a clue what you mean. Using S11 in your example above to arrive at SWR is incorrect.

@MegawattKS

3 жыл бұрын

@Jerry B The formula above is correct for converting S11 to VSWR, but only if S11 is taken out of dB domain into the linear domain. Sorry for not stating that in my reply. I used the word "dip" to mean where S11 dropped from a small negative dB outside the bands (e.g. -2 dB due to roundtrip coax feedline loss) to something like -10 dB or lower at resonance. For example, if S11 shows as -20 dB as it does in the 40m band, then the return-loss is 20 dB and the magnitude of S11 is |S11| = 10^(S11_in_dB/20) = 10^(-RL_in_dB/20) = 0.10. (Note that S11_in_dB = 20 log(|S11|) = 20 log(0.1) = -20, so this correctly took it out of dB and into the linear domain.) Using the formula given, SWR (or VSWR) is then (1+0.1)/(1-0.1) = 1.22 (or "1.22:1" if one prefers). Here's a nice page from Amphenol with a conversion chart from RL to VSWR to avoid all the calculations :-) www.amphenolrf.com/vswr-conversion-chart

@bkj242

3 жыл бұрын

@@MegawattKS I’m familiar with the conversions but I believe the point in all this were comments concerning the the S parameters and how each is represented irrespective of VSWR but as their relationship of their match to 50 ohms. Nothing more.

Hello! When you travel across the swr curve with the left and right keys… is it to adjust the steps? For instance, i find that mine goes from 7050 to 7150 or so… Thank you

@MegawattKS

2 жыл бұрын

I used the little 'wheel' (rocker) input on mine to tell it to move the marker. I don't know what the stepsize is, but I think the NanoVNA is limited to something like 101 steps across the range I tell it to sweep through. So for fine steps, I have to decrease the sweep range. In the video, I did that to get a better look at the 80m band. But something similar could be done in the 40m band. Sweeping from 7.0 to 7.3 MHz with 101 points would make it use a stepsize of 3kHz, which would be enough to get a good accurate look at how an antenna does over the whole band (one band at a time :-) ). Hope that helps.

Using the SWR scale instead of return loss is what most hams understand.

@MegawattKS

2 жыл бұрын

Agreed. That's what I learned first as well. But as noted in the video, radio engineers switched to S11 (or "return loss") when VNA instruments were developed and became widely used. SWR was developed based on the limitations of what was easiest to measure in the early days (max total voltage on line divided by minimum voltage on line). S11 is based on what the new instruments measure directly (reflected voltage magnitude divide by incident voltage magnitude). Fortunately the VNA can do either type of display - so we're all covered :-) 73's