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Re: Tantalum Capacitors

 

FWIW:
Here in Colorado Springs (dry climate, high altitude) I seem to have MUCH fewer cap failures than everyone else. I can't remember the last time I found a tantalum that was actually bad (and certainly not shorted). I have NEVER seen an exploded Rifa cap.
I *occasionally* find a dried-out electrolytic (especially in ordinary commercial radios and such), and some old paper coupling caps turn out to be a bit leaky in commercial gear (but almost never in higher-standard gear like HP test equipment).
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I *assume* that the dry air and/or high altitude is the difference.
I have NEVER felt the need to pre-emptively replace caps, like so many folks seem to think is essential. One of my 1960's-vintage HP machines had two examples of dried-out electrolytics of a specific brand/type, so I did replace a couple more of the same type that were in it (even though they were still working).
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Pete
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Re: Troubleshooting a 8591e with opt 130

 

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Marco,

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This is my measures about LOG/LIN switch

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The LM339 U108 has open collector outputs, as the graph shows, although it is not to scale with the configuration in your 8591E, but you can see that if the sink current exceeds 10mA, the voltage will quickly rise again depending on the current. If you ever had a replacement LM339, it might be a good idea to change it to see how it behaves, or by isolating the outputs one by one, see if the voltage drops back to the nominal value.

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Yves,
Re: VNA Resonance Methodology

 

Here's what happens if an attempt is made to measure the Q via a reflection method (s11) using a modern lab VNA.
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This is asking a bit much of the VNA as the reflection coefficient is very close to 1 and it is trying to make a vector measurement here. However, it did fairly well I think and it shows a Q of just over 130. The graph below shows the Rs and the Q across 1 to 2 MHz.
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You can see that the green Q curve is very noisy and there will also be additional uncertainties creeping in. The Rs is just under 4.5 ohms but the red Rs trace is also very noisy. This isn't a very trustworthy test method in this case.
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Re: VNA Resonance Methodology

 

See below for an image of a couple of my old Q measuring jigs. I haven't used these for a long time. The larger one mounted on pillars has a resistively tapped (low impedance) source and it has an active buffer with a capacitive tap at the input. This gives a really high input impedance and I used to use this to measure via the 3dB method. But I discovered that the passive method is usually adequate using E and H field probes. This allows both ends of the series resonator to be grounded and the resonator just gets tickled remotely via the probes.
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The smaller jig was an attempt to make an ultra low Z source up at VHF using a very low Z transmission line. The inductor gets connected very close to the ground end of the transmission line and then to ground. I then used to use an E field probe with it as the receiver.
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The insulator under the copper line is extremely thin. I can't remember how well this worked as I abandoned it in favour of the current methods I use. In theory at least, the source impedance was very low up at VHF.
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Re: VNA Resonance Methodology

 

Hi Ed thanks. In addition to what I described already I do have various Q measuring jigs here including one with a Hi Z amplifier as you describe. It's a bit of a mess but it does work quite well. I also use a capacitive divider at the input to the high Z amplifier to step up the input impedance. The risk with active buffers like this is that they can introduce negative resistance at the input and this can upset the accuracy of the process. So I tend to try and use the passive jigs as much as possible. However, I did try very hard to avoid having any negative resistance with my Hi Z buffer.
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To get low source resistance, I've got various options here. I have a low Z transmission line launcher and also a low resistance divider as used in some Q meters. However, these don't work very well up at VHF and UHF.
That's partly why Q meters don't perform well at higher frequencies. I prefer to use other methods like the shunt resonator method or the E and H field probe method. These have served me well for many years up at VHF and UHF.?
Regards
Jeremy
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Re: VNA Resonance Methodology

 

jmr,
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you can do the Q more directly with your VNA if you can add a high-Z RF amplifier, and likewise, some Z reduction at the source. The trick with Q-meters is to get ideally zero output Z in the source, and infinite input Z in the voltage amplifier. In the HP4342A these are around 20 milliohms and 100 megohms parallel 2 pF, respectively. These are hard to achieve in just wiring stuff together, so the DUT deck especially is quite a mechanism including the source, amplifier, and tuning capacitor, all built to minimize parasitics.
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With the VNA you can measure more stuff and figure out how to scale and compensate for everything, while the old Q-meters can't, so they had to rely on precision and performance up front.
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Ed
Re: VNA Resonance Methodology

 

The next test method I tried is the classic shunt resonator method. This relies on the VNA ports being exactly 50 ohms so I pad the ends of the cables with 15dB and 10dB attenuators to really make sure the source and load is close to 50 ohms. You can see this gave a resonator null at about -16.3dB at 1.48 MHz. The other way to correct the ports to 50 ohms is to do a full two port calibration of course.
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This method yielded a Q of 128.8 at 1.48 MHz as shown in the excel sheet below. This agrees very well with the 3dB bandwidth method although the 3dB BW method can show a higher Q depending on the impact of the self capacitance of the solenoid. In this case, there isn't much difference because the self resonant frequency of the solenoid is about ten times higher in frequency than the 1.48 MHz test frequency. I think if I revisited the 3dB BW method and used more averaging the 3dB BW derived Q might be just over 130.
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Re: VNA Resonance Methodology

 

Oops - I lisdexified it. It's HP4342A not 4243A.?? Ed
Re: VNA Resonance Methodology

 

Next thing I've done is to measure the Q using the 3dB bandwidth method. I can do this using various test jigs but in this case I tried doing it with the resonator up in free space and I coupled to it using E and H field probes on port 1 and 2 of the VNA.
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The aim is to start with strong coupling and measure the Q using the VNA. The Q will be artificially low here because the loading of the probes will dampen the Q of the resonator. Then the aim is to gradually weaken the coupling until the indicated Q stops reducing with weaker coupling.
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I typically saw a Q of between 128 to 132 at 1.48 MHz with this method. I had to use averaging. The netbook PCB works in tandem with the VNA over GPIB to constantly request the Q to be measured in real time. It measures the Q quite rapidly using this method. However, because of the noise on the trace, it's difficult to get a precise reading. It was typically about 129 or 130. See the image below.
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Re: VNA Resonance Methodology

 

Here's yet another approach. One of my projects from some years back was to build a Q-meter front end - power amplifier, impedance converter transformer, high-Z RF amplifier, variable capacitor, and DUT interface - into a box. The box would be hooked up to my 8568B and its tracking generator that I built for it long ago. This all forms a swept-frequency Q-meter covering whatever frequency the transformer and amplifier can handle (about 20 kHz - 100 MHz in this case). The display is of log Q (dBQ) versus frequency, so has direct readout and very wide dynamic range. Compared to a regular Q-meter, there's no hunting for resonances with knobs and meter, no Q range switching needed, and you can tune the cap and see real-time results. You can zoom in to see more detail as with any SA.
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I had much of it built a couple years ago, and had done some preliminary experiments with the SA and TG setup - it was pretty slick. But, after all that, I happened to find a working HP4243A real Q-meter for a good price, so my need for completing the project was greatly diminished, and I shelved it. Someday I may be able to finish it up, but there's still a lot of work ahead. Another option that now exists is to modify the 4243A so it can work with the SA/TG to do as I originally intended, but with the precision and done-ness of the real thing. I've studied the situation a little bit, and it seems fairly straightforward to do it, but I want to be very careful to keep it working right in both stock and modified modes, and of course to not hurt anything. It's an electro-mechanical wonder, so tricky to work on. For now I'm happy to even have a good Q-meter.
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I started this project because I wanted a Q-meter, but had no prospect of ever even finding a 4243A, let alone getting a good deal too. I wouldn't bother with the old Boonton 260 vintage types - too much trouble for me. This sort of thing has happened to me often over the years, where I can't picture ever getting a certain kind of commercial gear, so I try to build a reasonable substitute. Then after lots of work and possibly years or even decades, I stumble upon the real thing.
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Ed
Re: Troubleshooting a 8591e with opt 130

 

Hey Gordon and Yves,
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Thanks for the advice! I had a look there before but I was wondering if it really is different from the CLIP that's freely available on the keysight website.?
Because the artek website states part number 5963-2951
That same number is in the CLIP on the keysight website:
Are you sure that it is indeed different from the 8950A?Clip as can be found here: ?
It might indeed be good to have the proper manual.
Let me know.?
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Yves,?
I did more measuring on the Log amp, my earlier Lin mode voltages were partially incorrect.
The actual voltages are:
? low high
G4 14,238 -3,719
G5 14,238 -3,577
G6 14,238 -3,075
I was expecting around -7.4 V as in your analyzer. I checked the potentiometers, all seem connected but they can't be adjusted anymore negative then about -4.5V.?
Thinking something must be wrong I checked the different voltages. The +10VF, the -8VT, output of the voltage divider R110/R111 (1.175V), the output of U108A (14.2 / -7.9)?
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The input on the gain control, I checked the +11V1, and IFG6 (14.2 / -7.9), but still G6 goes to -3.0.
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Assuming it must be the loading of the circuit behind the gain control lines causing the issue I also checked voltages on the 5th gain stage.
again the +11v, -9vf2 seem ok. The VLOG1 switches between -8V in Log mode and +10V in Lin mode.?
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My main question would be what your VLOG1 is in Log and Lin mode. Unless ofcourse you have a better idea on what to measure.
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Marco
Re: VNA Resonance Methodology

 

I managed to get some 0.4mm diameter wire and the datasheet suggests that the enamel adds about 0.06mm to the diameter.
To get close to a 31mm former I had to wrap some masking tape around an existing former that was otherwise a bit too small.?
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The former now measures about 30.6mm diameter.
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When I wound 49 turns on it the coil length was 22.4mm. If I punch these numbers into my software program I get 64uH and a Q of 127 at 1.45 MHz.
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When I measured the coil with a VNA it showed 63.1uH which is quite close. It's difficult to maintain perfectly close windings at all parts of the winding but I did try and get it very close.
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To show how easy it is to use a VNA to find the resonant frequency when used with a resonating capacitance, I put about 185pF in parallel with it to get it resonant close to about 1.45 MHz. I then stuck a video showing this on youtube.
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Click on the link to the Youtube video above to see how easy it is to find the resonant frequency and how the null is stable at the same resonant frequency no matter how close the test loop gets to the resonator. I used a 6cm diameter loop at the end of the VNA cable and selected an s11 measurement at 0.5dB/div. There is no need to calibrate anything on the VNA when using this method.
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This is MUCH better than fishing about in the dark with an ancient GDO. If the cap was a variable cap you could see it tune the resonant frequency in real time. Hopefully this ends the argument against using a VNA for this test.
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Re: VNA Resonance Methodology

 

Yeah, it's not trying to solve Unified Field Theory, but just looking at some common engineering problems from different perspectives and methods. It's good to know of various approaches and understand the possibilities and limitations, and relationships. At least here they should all ultimately agree mathematically and physically. It's good exercise for the old neurons too.
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Ed
Re: Troubleshooting a 8591e with opt 130

 

Hi Marco

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If you go to Artek manuals ? ? ? ? You will find a clip for HP8591E it comes with several other related files in PDF format 11 in total all for $25 US. I could see you were not following the correct schematic diagram which will not help your fault finding. All you need is to have is a drop box app installed to receive the files.

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Gordon GM1THS

Re: VNA Resonance Methodology

 

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Entire topic is a bit odd
I agree a bit with this idea but in this group we surf all time between the old an new measurement methods and equipment. In this sense the analysis of different measurements techniques and the way to do it with the new generation of instruments I believe is a great experience specially to teach to younger people.?
I found amazing measurement methods on 1950s papers , forgot because it where difficult and/or inaccurate ¡­ with the 50s tools¡­?
The actual electrical engineering students has no idea about Q-meter and also has no idea how to measure an inductor. They put the question in google¡­ and the best result is an expensive LCR meter , this is a box with a user manual. Many of them have no idea how it works.?


Ing. Patricio A. Greco
Laboratorio de Calibraci¨®n ISO 17025?AREA: RF/MW?
Gral. Mart¨ªn Rodr¨ªguez 2159
San Miguel (1663)
Buenos Aires
T: +5411-4455-2557
F: +5411-4032-0072




On 29 Nov 2024, at 09:53, jmr via <jmrhzu@...> wrote:

On Fri, Nov 29, 2024 at 04:27 AM, Froggie the Gremlin wrote:
Entire topic is a bit odd
Not really. A modern VNA is a very versatile tool. The original question was about using a VNA to test the resonator for resonance so I've tried to show how a VNA can be used in a way that will easily outclass a traditional GDO.
It takes a bit longer for the VNA to boot up and set the start and stop frequencies and add the cable and loop antenna but once this is done, the reward is ease of finding the null and increased accuracy.
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I've also used some software to predict the inductance and Q of the test coil based on its dimensions.
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I've also suggested ways to use the VNA to measure Q.
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I don't see how any of this is odd as the OP has a VNA to hand and had already tried using a GDO.
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Re: VNA Resonance Methodology

 

On Fri, Nov 29, 2024 at 04:27 AM, Froggie the Gremlin wrote:
Entire topic is a bit odd
Not really. A modern VNA is a very versatile tool. The original question was about using a VNA to test the resonator for resonance so I've tried to show how a VNA can be used in a way that will easily outclass a traditional GDO.
It takes a bit longer for the VNA to boot up and set the start and stop frequencies and add the cable and loop antenna but once this is done, the reward is ease of finding the null and increased accuracy.
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I've also used some software to predict the inductance and Q of the test coil based on its dimensions.
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I've also suggested ways to use the VNA to measure Q.
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I don't see how any of this is odd as the OP has a VNA to hand and had already tried using a GDO.
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Re: HP 8341B 1992 firmware version

 

Hi Saevar, Dmitrij,
Thank you very much. In that case I will order 4 eproms and I will try to do the upgrade. I hope it will work. Thank you very much once again.
Regards,
Wojciech
Re: Troubleshooting a 8591e with opt 130

 

Yves,
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The schematics in vol 3 of those files include the Analog board, this schematic seems to fit the board in my 8591E much better.
There is only RF10, RF30 and RF20 for the attenuator but it is still IOB12 switching RF10.
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RF10 switches, as i can hear and see it. So IOB12 must be functional.

Since the other IFA lines function, the Cal_Atten signal must also be functional. So strangely it seems the CPU just doesn't enable the 16dB IFA5. Since with the 74LS374 the output is still stuck low. Then I found the following:
It seems IFA5 is never used. I guess I was looking for a ghost.. But then the question remains why my analyzer is off 15dB.

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I'm going to have another look at the G4/G5/G6 Voltages.?
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Marco
Re: HP 8341B 1992 firmware version

 

He just make error when write firmware to EPROMs.
Re: VNA Resonance Methodology

 

Entire topic is a bit odd

These instrumenbts are "different animals"

VNA is used in a constant Zo environment eg with filters, amps, mixers, dir couplers all at 50 or 72/75 Ohm. See HP notes on VNA.

GDO are specific to find res freq of a tuned ckt isolated or in the ckt (in TX, RX etc) without removing the tuned ckt.

Q meters ( Boonton 160, 260A) have a special oscillator and thermocouple RF meter that sets a fixed current eg 1.0 A thru a connected coil .
A wideband low R series (1 m Ohm? ) and RF meter give the Q directly as the osc is tuned. See Boonton app notes and papers.

Each has different capabilities.

We have gimmicked a resonance test with old HP audio osc, a 10 k resistor and scope or AC meter ....

Just common stuff and zero cost.

Jon
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