Playing around with an impedance network analyzer 4cx3000.

Added: 2026-05-13

[00:00:00]Good evening, YouTube. Needle Bender 785 here in Florida. Welcome to the weekend with another uh Ford CX3000 video, but this one is going to be trying out this new piece of equipment that I got. It's an HP 485 alpha.

[00:00:20]Um, it's a vector impedance analyzer.

[00:00:25]It's a very expensive piece of equipment, but it's specifically designed to analyze um impedance shifts in tuned circuits or in any kind of a resonant circuit to determine whenever a phase shift occurs or which actually always coincides with the resonance of the circuit. And what we're trying to determine is the self-ressonance of this coil right here.

[00:00:54]And um I've ran into the past actually with this specific coil and like I said this is on my own amplifier. I've actually pulled this out of a amplifier I was building for a customer about a year ago and haven't used it since because on 15 m it actually started smoking. Not enough to actually damage the coil. The coil is perfectly fine but it actually um started smoking and was about to catch fire.

[00:01:24]um on 15 meters and on every other band they work perfectly stay cool.

[00:01:30]And a phenomenon that actually takes place is the self-ressonance in the windings itself because but there's other actual actually other factors that go into u that actually come into play here um other than just a inter winding capacitance which uh you know parallel capacitors and parallel inductors create a tuned circuit and there is always going to be a frequency. You're not going to get one of these that's not going to be resonant on some frequency.

[00:02:02]But if you ever look at if you ever look at um um some commercially available um uh plate chokes, they come spaced out in three little segments here. And some of them have a ferite rod. Some of most of them don't. They come spaced out. Then there's very u lightly wound areas and then there's heavily wound areas. and that is actually to to set the self-ressonant frequency into a frequency range that is actually outside of any known band of operation. Uh the last one I bought for for that particular amplifier that I sold actually had a resonance frequency of 10.5 megahertz which is not any kind of ham band or any kind of band that anybody talks on. So, so what we're trying to determine here is what is the self-ressonance of this circuit and what is the frequency that this thing is going to uh get hot on.

[00:03:02]So, for this purpose, we're going to employ this fancy um analyzer. And this is a high impedance um vector impedance analyzer.

[00:03:16]and we're going to first thing we're going to do is we're going to fire this thing up and we're going to see. So the full scale on the left is set to 100 ohms. So right now we got 100 ohms. That means it's we're in perfect resonance and we have a we have a um a phase shift occurring here 90°. So full scale you got 90 plus 90 minus which is 180°.

[00:03:44]Whenever you have a 180° shift occurring, you know you have um a perfect resonance. So right now we're our scale here is set between 1.5 and 4.5 MHz and we are right now on 6.5 6.5 MHz. So we do have a a resonance point here right at 6.5 MHz as you can see. perfect 100 ohms and um 6.5. But there is there is a secondary there is a secondary resonance point which we're going to find here. This one we don't really care about because so as you notice as I keep turning this higher, we're going up in frequency here.

[00:04:36]Our impedance starts to drop off and our degrees start coming up.

[00:04:42]Actually, as you can see, it went completely completely 90° shift as we got closer to the other other end of the band around 15 megahertz. So, we're going to go up to um higher band here.

[00:05:01]Uh now we are let's see we're on we're around the there's no resonance going on. We're on the 40 m band now.

[00:05:12]I'm sorry, 20 m band now.

[00:05:16]And there is no, as you can see, that needle is showing zero impedance. As you can see, as we're turning it, that needle is going, the needle on the right, which is our phase, is starting to move sharply to the left and the needle on the left is coming up. And that's what that's what we call a phase shift.

[00:05:41]And as you can see, we're running out of scale. So on this scale, we're not showing any perfect. We're showing some phase shifts, but we're not showing any anywhere where it's fully fully resonant. So, we're going to go up to the next one, which is 14 14 through 35 MHz scale, and we're going to see if we can find that perfect 100 ohm impedance, which we actually are running into right now. And an angle shift of 90° just about.

[00:06:20]There we go. And we are on uh 18.5 megahertz which is uh kind of very close to that 15 meter band. So we do have a resonance here at the 18.5 MHz which again which is actually more very pronounced resonance point. So, we got one here and we're going to go to then if we roll off, as you can see, the angle starts to drop off and impedance all the way through the roof now. So, we're off of the peak. So, that means it's not resonant there. So, as you can see, we tune. It's a very narrow V. If we would use a VNA, which in this case, a VNA wouldn't really help.

[00:07:12]As you can see, our we're getting close to that 90 degree 180 degree shift, which is 90 degrees each direction there. And we're looking for that one there.

[00:07:26]It's that mark right there. As close as we get to that mark.

[00:07:31]There we go.

[00:07:35]So that right there, right at 18.2 meghertz, I would say 18.2 2 to 18.5 is a resonance point. And again, we're not talking on that band, but we need to know what are we going to be self-ressonant at, which something that's very undesirable to have. And a lot of factors affect that. Like, watch this. So, I'm going to place a screwdriver just near that area.

[00:08:13]And you can see some shift there. Um, but mostly it's the resonance of the choke and the the network, the capacitor, everything. It's going to have a self-ressonant point.

[00:08:28]So 18 and when we go to 19 MHz you can see that angle starts to drop off and impedance is off the chart.

[00:08:42]So you can tell that's not a resonant point. So let's go up higher in a band.

[00:08:47]Let's go up to 35 megahertz.

[00:08:50]And as you can see totally no No resonance there.

[00:09:02]And then you get an angle shift again to the other side.

[00:09:07]Now we're on.

[00:09:20]So some kind of an angle, some kind of a not a strong resonance, but we got a resonance of it goes from zero ohms to there right at about uh let's see 35 36 37 megahertz. So there is a there is a resonance point there and then it goes away after that. So just just some very interesting analytical measurements here as we go and you can see it fluctuating because like I said even ambient air and ambient metal presence around it affects that.

[00:10:04]What we're just trying to make sure that none of these resonant points occur on the frequency of operation and uh that's a new piece of equipment I got a couple months ago. Haven't really played around much with it, but um figure I'd make a video. It's a really neat piece of equipment. It's a very very high-end measurement device specifically designed to um to measure self-ressonance and selfosscillation of uh different different u inductive devices and capacitive circuits and stuff like that. So obviously over here we have an inductor but it also has um interwinding capacitance in between the windings which causes uh it to have a um a self-ressonance point. So we kind of I kind of figured I'd do a video on why you know in one of my previous builds this thing nearly caught fire on 15 meters. And this particular choke is going to be perfect for this amplifier because this amplifier is not capable of 15 m.

[00:11:12]It just doesn't have that. Some progress here. This thing is nearly done. Uh screen relay was added. Um let's see. This needs to be mounted.

[00:11:25]It's a grid supply. Um everything is mostly wired up. A relay bank, everything. But the pretty much what I was what I've been working on. And let's see what else was done.

[00:11:39]Uh high voltage connector has been installed. Capacitor.

[00:11:45]There's our high voltage connector which uses the our dedicated high voltage connection. I'll show you what that looks like.

[00:11:55]So for high voltage cables, we only use we only use this type of connector.

[00:12:02]It's a very specific high voltage connector. It's rated for 10 10 KV DC voltage.

[00:12:10]But the the nice thing about it is first of all you have to assemble this yourself. And after I assemble them, I always hypot test them to like 15 KV with a low current, high voltage um generator. Just make sure we're not drawing any currents, no arcs or anything like that. And these things work flawlessly.

[00:12:30]Um, this also provides another u another source of ground because this is a shielded cable and it provides a source of ground. So you cannot connect this to the upper deck without having at least a ground source. So, it's kind of a it's a backup for one of the three backups or four backups that we have as far as source of ground goes.

[00:12:56]And um these connectors run about on eBay, they run about $100 for a set. And there's some other US uh companies out there, they sell ceramic versions for I don't know, three times the cost. So, I would probably And the build quality on these is phenomenal. I have not had any issues. I had some I had an issue where I screwed up with thread on my own and had cross threaded something, but that was not the fault of the connector. The connectors are actually really good.

[00:13:31]Show you how they work here. So, whenever somebody connects it, it inserts all the way here.

[00:13:40]And that was a probe. And you just screw it in like a PL259.

[00:13:46]And as you can see, it goes in about two and a half inches there. And it's fully shielded. And then it's also encapsulated in uh some shrink wrap.

[00:14:01]But anyway, this thing is just getting it some finishing touches on. I still got to build a wall around this transformer case to this transformer and make a case there.

[00:14:15]This is the actual probe that came with this thing. It's It's really got some weight to it. It's some really nice piece of equipment there.

[00:14:26]But anyway, just wanted to share some u some interesting uh analysis I kind of uh wanted to demonstrate as far as um why these things sometimes can heat up, sometimes can um sometimes a section of them will heat up. And um like I said, there's a phenomenon that's called self-ressonance that actually happens in every single choke. It's a matter of the the question is are you h do you happen to be transmitting on that frequency and that's what we're here to find out.

[00:15:00]Anyways 73s thanks for watching Needle Bender 785 here in Florida. We're back on the side.