Could your peak be caused by the "ground lead"? At MHz it is going to look like a inductor. I am usually wrong but then I would rather be happy than right any day. After a bit of poking around , if you look up HP Journal Vol 2 No 3 it appears you need a special HP widget (HP455A) which is used to connect the probe to a coax line, eliminating the need for a ground lead, to measure MHz.

@notimetolooz9655

4 ай бұрын

I was going to suggest that also. The original HP adapter is more of a coaxial connection.

@ddowlingau

4 ай бұрын

With original HP adapter shown at "13:25" the probe tip and ground lead are removed and the whole probe body is screwed into an adapter. This almost certainly would have a much lower inductance. Time to fire up the milling machine :-)

@projectartichoke

4 ай бұрын

I bet you're right about that. High frequency grounding is very special and mysterious.

@CuriousMarc

4 ай бұрын

Good suggestion! The ground lead is that black lead direct from the body of the probe to the tee. Short of machining an adapter like the original, one way to test would be to put a small resistance in series with the ground lead and see if that kills the resonance, or lengthen it and see if the resonance goes to lower frequencies. Let me get in the lab and check that out…

@user-ku8bh5oe9j

4 ай бұрын

The datasheet for the probe suggests an input capacitance of around 1.5pF which for resonance at around 700MHz requires about 40nH of inductance. A back of the envelope calculation suggests that about 50mm of ground lead length would give you this. Difficult to know the lead length from the video but it would be Interesting to know if theory and practice vaguely correspond.

Oh man, I was soooo lucky that a clean AC probe showed up on ebay for $49. I immediately broke my mouse clicking the buy it now button, and it works perfectly! Legend has it that SOMETIMES...... an ebay seller slips up and doesn't go for the first born. I absolutely LOVE this meter.

Thank you, Atkelar! Looking forward to seeing how you get along!

@t1d100

4 ай бұрын

I have seen Atkelar's video. He did an amazingly good job. Well worth watching.

@vincei4252

4 ай бұрын

@@t1d100Thank you. Will be watching it today.

15:56 Ohhhh YEaaah! Let's plot that data baby, with the HP data plotter. How cool is that. Restoring things with OTHER things previously restored.

I just found Atkelar a week ago and now he is in your video. The world really is small.

Congrats on 200K, Marc. Well deserved!

@markgreco1962

4 ай бұрын

Woo hoo Marc and gang.

I used to use the 410C to service 1960s and 70s communications equipment, mainly because that was what was specified in the test instructions; I wasn't aware that it was a valve / vacuum tube voltmeter.

It makes me feel a lot better to see that even a seasoned pro like Marc still sometimes reaches for the wrong axis knob on the scope! Great video, I always hit the like button before the video even starts and I never regret it.

Marc, we need to get you a HP 3400A. It just needs to happen. You’re the right person to appreciate it!

I also got a 410B missing the AC Probe that I plan on restoring someday if I manage to find a probe for it. Greta work Marc!

I think the parasitic inductance causing the peak is the short ground lead. I would get a piece of thin copper strip or ribbon about 20mm wide and connect the grounds together as close as possible. If this reduces the parasitic inductance, then the resonant frequency should go higher, and hopefully the peak will not be so sharp.

Soon may the HP probe materialise! Meanwhile it would be great to see you playing along with the melody line of the channel theme aong on the Juno 6

Nice work! And yes, I went over to Atkelar. Great channel. Subscribed right away. Good collaboration.

I love the font on this old HP test gear, it's the same on my HP120B scope and my HP8551B SA. Thanks for posting.

When we used the 410C for analog TV transmitter testing, we used the. MODEL 1I042A PROBET CONNECTOR, (I'm not shouting, that's how they appear in the manual) in line with the coax transmission line, which was then terminated with a 50ohm Test load. We would read the voltage across the line, then grab a calculator & derive the "sync tip power" as the detector is a "peak & hold circuit". This was only used for the lower power transmitters, up to around 2kW. Another accessory which might be more appropriate for testing would be the MODEL 1I043A TYPE N CONNECTOR, which is not a T connector. Both of these appear in paragraphs 1-11 & 1-12 respectively of the manual's "General Information " page.

Atkelar is a great dude and he runs a fantastic channel. Glad he got a shoutout here!

Mission accomplished, as usual - 👍!

wow, atkelars channel is great !! thanks! left him a like, subscribe, comment and bell :D

seeing that recorder in action was pretty cool :)

Always interesting!

I love the instructions for the lamp- "30k ohm resistor in series with the lamp across 105-125 VAC"... I've now got a weekend project!

I am a bit worried about the replacement 22MΩ resistor. I think the replacement is a metal film, and they are normally made by milling a spiral, an inductor, in the surface of the resistor. It might be that You will get rid of the oscillation if using a carbon composite resistor instead.

@carlpettit7754

4 ай бұрын

Carbon will be ok providing it is not solid. solids go up in resistance as the frequency goes up. This is due to skin effect.

Try a couple hundred ohms in series with the probe tip. A tip for finding parasitics: come up with reasonable (even if ballpark) estimates for L and C, or Zo and Fo. You've measured Fo here, and judging by the Q factor of the curve, Zo is either ~1/10 or ~10 times the source resistance, depending on if it's a series or parallel resonant circuit. Source resistance is 25Ω, since it's a terminated 50Ω line (the power sensor is a termination, right?). So it should be in the ballpark of 50nH and 1pF. Another tip: inductance is proportional to length: consider the magnetic constant 1.257 uH/m. If we multiply by length, and scale by a dimensionless geometry factor, we get inductance. For an apparently so-high impedance (compare 250Ω to a more typical transmission line 50~150Ω impedance), the geometry factor will be on the high side, 0.5-1 say, so 50nH is about two inches of lead length. And gosh, I wonder where you can find a couple inches in the probe tip structure? Aha! :) The peaking is valuable, actually, for extending the frequency response; if overdamped, R*C dominates and it rolls off gently at some 100s MHz. Underdamped, you get a peak right at the cutoff, which is the observation here. In principle, you could add a capacitance plate somewhere in the RF loop to add a second pole, getting a 3rd order peaked response overall. This could extend response to, maybe 800MHz or so -- but with the ground strap sitting just wherever, and with trying to solve a 3rd order polynomial by way of cutting and positioning mechanical parts... I think you'll agree that's the kind of optimization best left to the old HP boys, hah. Put another way: the famous Tektronix T-coil peaking, but at RF where you don't use coils but bits of metal.

Enjoyed. Thanks 😊

Maybe the resonance is in the cable and input cap. Those chokes might be to blame. Extending the cable should prove it.

I have a 410C with all the probes. I have opened it after seeing this video. It appears to be solid state, no tubes inside, but does have that AC probe. If you are interested let me know.

Провод массы из зонда идёт по дуге , его индуктивность , совместно с ёмкостью вакуумного диода , образует последовательный колебательный контур , поднимающий АЧХ. Его бы , хотя бы , алюминиевой фольгой облепить.

Wonderful!

It is important to have a terminator at the end of the cable. Do not use a T with a cable to go to one of the instruments. This creates stubs which will resonate. Use a single run of cable with the instruments tapping off it. Terminate at the far end. In summary, a single run of cable with the instruments tapping off it terminated at the end. No cables going off to instruments, connect directly to them.

My Genrad VTVM RF probe has a 50 Ohm load that fits into the GR874 connector on the probe input. My Boonton RF voltmeter also has a 50 ohm input that fits on the probe. They work up to their specified bandwidths with the integral 50 loads and coax inputs. When used in probe mode with a ground lead issues start at high 10s of MHz. Perhaps you need to make a similar coax terminated input that fits on the probe and allows you to eliminate the ground lead inductor.

There was a tiny bit of cleverness, on the end of the pin of the original probe resistor. Did anyone else catch it? @19:41. The original builder slid the insulation tube onto the pin and, then, bent the end of the pin 90 degrees. This prevented the insulation tube from sliding off and/or sliding out of position (which might allow a gap in coverage,) while the builder fished the resistor pin through the body of the probe. Is this mind boggling cool? No, but I will take any helpful building method tip that I can get... Cheers.

The capacitors at the coaxial cable ends probably peak the top end response . Don't overlook the cable type & length “ Capacitor - inductor - capacitor ” . We are talking HP so its probably non standard cable . Also the HP probe body looks like it has more RF screening . Everything is important at vhf even the type of resistors .

Ground wire. Try different length (shorter), multiple grounds (lower inductance). Regards from NZ, great video.

At high MHz range, the ground lead loop is a killer. You might find a Tektronix application note about it. I have been at their seminar about oscilloscopes and their probes, where they showed scope photos for comparison. In the scope probe, the inner element is 9 M-ohm, bypassed by a small adjustable (case) capacitance, some 2 to 4 pF. You have a different, hugely larger capacitor as the main longitudinal element. With that, the resonance even with a minimal ground loop inductance is radically more evident. But a finer point - the resistor you applied is also suspect. Its element has been trimmed by cutting a spiral, which means it became also a tiny coil. The old, 5% (or 10 or even 20%) carbon composition resistors did not have any spiral cut in their element, and had lower inductance. The question might be just, is your resonance by nature series or parallel type…

Terrific! I have such an instrument in my stash. Is there a way to achieve AC measurement without this diode tube but with semiconductors instead?

I'm so curious about what Master Ken is up to in the background!

@CuriousMarc

4 ай бұрын

He was hard at work for weeks on his analog mechanical computer. It’s all working now. Video coming out soon.

I wonder if the big peak is a result of the power sensor feedback.... maybe try doing it open loop instead to rule that out. Ideally you have a terminator on the cable to kill the resonance at the probe end, I didn't see one there, you could have used a pass through terminator to help it, obviously it would throw the reading out a bit but will stop the resonance and rule out the test setup as the problem.

Two words: Through Terminator Unless that power sensor off the T junction you have for the generator’s ALC has a 50Ω termination, you may be hitting a standing wave extremity (either peak or trough)… potentially further exacerbated by the ALC feedback loop, wherein the process of the generator compensating itself, it’s dumping higher power down the line at that frequency. A better setup might be to swap the T-junction with a balanced power divider and a through terminator on each side (provided, the generator can normalized to a fixed -3dB detection offset)

@X5Industries

3 ай бұрын

Should also add: a very simple way to verify/rule out standing wave effects as the culprit would be to connect a different length of cable between the generator and T junction)

Your ground antenna ah lead is probably the source of your problem. A test fixture that minimizes the loopiness of the ground connection would be good. You'd also want a metal band around the meter end of the diode around the R and C components. I have problems explaining this to my partner. But, basically, you do not want loops of wire in your measurement path. You want everything short and direct. Thus the fixture should have a nice cable shield to probe shield machined fixture. That will change the performance by raising the frequency of that sharp peak. The wire in the tubes can't be mitigated. So that limits how far you can move the resonance. RF behaves somewhat intuitively until you get above maybe 100 MHz. At that point even the PCB between two ground connections on a nice ground plane starts to become a component rather than satisfying the "ground" abstraction. Mostly, though, I don't press my luck by going above 1GHz. I don't grok that stuff the way I grok lower frequencies. {^_^}

Great as allways -- Just got an ebay HP410C -- the manual shows an alternative amplifier with FETs, but the instrument still has the chopper ones. I will test is soon, but before I plan to recap the power suplly CAP CANs. with 2x1200uf -20V to 1x 4700uF 25V and the other 4x20uF 450V to 4x 27uF 450V waitong for them to arrive --Have you checked the CAPs in your device, they are really old I assume ? I wait for plugin of the power till changed, though the ebay seller did power on the device but without further check. I also got the original probe, and will make some tests after you had such problems with the other probe, will be interssting to see if theoriginal probe has some similar problems.

@CuriousMarc

4 ай бұрын

The can caps in my unit were fine, but one of the caps in Atkelar’s unit were bad. It’s probably a good idea to replace them both.

directly atkelar addad to the watchlist

Hi Marc: Is the OP of the RF Synthesizer / probe correctly terminated in 50 Ohms? If not, that may be a factor in the rising response.... Steve

@CuriousMarc

4 ай бұрын

It is terminated at the tee by the power probe. At 700 MHz that should be “close enough”. At least I thought so, now I’m doubting everything…

@stevemahrer7097

4 ай бұрын

Maybe try a VNA, that would show any mismatch and the frequency at which it occurs… I would imagine you have a few lying around!

Your peak could be caused by the construction of the resistor. I will probably be a spiral wound film. I had this on a cheap VSWR meter at 900Mhz or so.

Hold up… can we talk about this puppet situation? I feel like you sorta breezed over that.

Why is the Agilent scope at 8:52 running Keysight software?

Yay another furry! Awesome job helping out!

The oil on your fingies really changes the resistance?! Or was that feller being cheekey?

@CuriousMarc

4 ай бұрын

It does, on very high resistor values like this 36 MOhms. And Eric is **always** cheeky.

Two!

It looks like your coaxial cable from the signal generator is not terminated with pure resistance. What's likely happening is that your connecting cable is acting like a 1/4 wave transformation, causing the voltage peak - and the paralleled cable/load on the "tee" connector to the scope doesn't help either. Adding a 50 ohm termination at the scope may have made it "less bad". Connecting multiple devices in parallel will be tricky as any deviation from 50 ohms resistive will skew the results: One may be able to put a terminator at the "tee" - or perhaps a 20dB pad (measuring voltage through it - also terminating at the 'scope - and then doing calibration to compensate for the loss when using it to make readings) - and live with the parasitic reactance of the tee itself and the probe - which should be far, far less than the set-up you used. Constructing such a fixture for even 100 MHz will be a bit of a challenge it it's likely that inconsistency/lack of flatness would more likely be a result of its imperfection than the probe itself.

Was that a 410 probe, Rasputin was using in Hellboy ?

I have a couple of the rectifier tubes of your interested?

Did a double take at "NE2-KZreads" and wasn't enlightened until the spec sheet popped up on screen

11 MHz!!!

I abandoned a video by Aldo Sterone on Boeing's loose nuts (in French) to watch this.

@jeanpierre3193

4 ай бұрын

Exactly the same things!!!! incroyable!!

@vincei4252

4 ай бұрын

Boeing has a lot to answer for.

@SubTroppo

4 ай бұрын

@@vincei4252 Nothing another stock buy-back won't cure (sarc.).

@SubTroppo

4 ай бұрын

@@jeanpierre3193 Great minds think alike (fools seldom differ).

@scowell

4 ай бұрын

Blancolirio always has the good aviation info.

It's a well-known fact that Hickock copied the Tektronix 545 'scope. I'm not surprised that they copied HP's 11036A probe...

@benjaminhanke79

4 ай бұрын

Ah, Hickok is the Brand Name, I was a bit lost there.

First view!

@CuriousMarc

4 ай бұрын

You are! You get awarded a free resonance at 700 MHz. I want to get rid of it…

i have one old 410c to sell if anyone is interested

TOO many ADs

@CuriousMarc

4 ай бұрын

Oh no, Google did it again. They autimatically add ad nreaks behind my back! I deleted them all but the standard one in the middle. Thanks for letting me know.