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VNA Resonance Methodology
Greetings, gentlemen,
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Earlier today I was trying to establish the resonant frequency of a tank circuit I'd put together. A simple enough task, you might think - as indeed it should be! Now since I was using really old-style components: single layer air-core inductor with air-spaced variable cap I was expecting pretty good Q and a marked 'dip' with my GDO.? Fo in this case was intended to be 1.45Mhz. Anyway, I couldn't get a reliable, repeatable dip so thought I'd switch to using a VNA instead. So I put a 50 ohm resistor in series with the tank and hooked it up to the analyzer. Sanity check: the tank is a parallel arrangement so therefore a 'rejector circuit' (high impedance) at resonance. So testing for S11 (reflection) with the Smith Chart display selected, I was expecting to sweep from 1Mhz to 2Mhz and see a dot/short line on the far right of the chart for the vast majority of the sweep, whilst seeing that move to a dot to dead centre at 1.45Mhz. But that's not what I'm seeing. Have I missed something?
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Cheers,
Jinxie |
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Re: Troubleshooting a 8591e with opt 130
Yves,?
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Thanks for the elaboration, you clearly know a lot about these machines!
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The probe I used was an old Agilent N2862A 10M // 15pF probe, so that's rather high capacitance compared to yours, that might cause some additional influence.
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One thing caught my eye from your post and it's giving me an eerie feeling. My amplitude peaks don't change when I switch Correct on or off.?
See the two plots below, sorry the indicator line is slightly misaligned but left is Correct ON, right is correct OFF. The main difference is in the noise floor.
Somehow the machine doesn't see this as a correction? Perhaps that's also why there is no fault in the selfcal and conf check while being 15dB off.
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All my previous measurements I just did a full reset to factory default cal because I already noticed that the difference wasn't there with just correction on and off.
Apparently your spectrum analyzer does properly switch correct on and off.?
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I can do the same measurements this evening, filling that table to see if we get some more clarification.
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Marco
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Re: Troubleshooting a 8591e with opt 130
¿ªÔÆÌåÓýThe RF signal goes through the 3 converters and then goes to the A11 filter module, then to A12 Amplitude control, A13 filter. At this point we have the AUX IF signal available at the back of the instrument at 21.4MHz. From this point, the signal can take two different paths: the one from A14 LOG-LIN amplifier/detector for the standard resBW from 5MHz to 1kHz, and finally the second path, option 130 which contains narrowband filters (300Hz,100Hz,30Hz...). Option 130 has its own LOG-LIN amplifier/detector. The output of A14 and option 130, is the AUX VIDEO signal available at the back of the instrument. Depending on the selection of the resBW, a multiplexer will choose one or the other. ? So, the question arises, since the signal for option 130 follows the same path to the input of A14 (AUX, IF) and option 130 does not have a level problem, then logically the problem would be with A14 LOG amplifier/detector. This would be true, if no other conditions change from the previous circuits when switching between option 130 and normal mode with A14. ? I checked all the data we took, and the data at TP5 gave us some similarities and some not. But our probes did not have the same impact on TP5 (hot spot). I would say that TP5 may not be the best point of comparison. ? The probe effect: Your probe mkr level with probe on tp5 mkr level no probe Log -14.2 -4.3 Lin -21.6 -20.2 You get 9.9 dB with or without probe for LOG mode, and 1.4 for LIN mode. ? In my case mkr level with probe on tp5 mkr level no probe Log -25.9 -20.0 Lin -23.1 -21.2 I get 5.9dB with or without probe for LOG mode, and 1.9dB for LIN mode. The probe used TEK P6138 10MOhms 10pF. ? ------------------------------ I studied your comments about the two SELFCAL videos. On my Spectrum, the video display limiter was enabled, that's why the limiting level is different. But in the following image, I have disabled it. ? I take the example here of the 1MHz resBW, but the remarks apply to all filters between 5MHz and 1kHz. During the amplitude calibration, the filters are aligned to have the correct filter width. We see that the signal is limited at the top of the screen, but this is not the real limit, by putting a marker we can find the limiting point. With this configuration for the 1MHz filter, in my case it is -6.57dBm. I used an external signal to find this limitation. When the 1MHz filter is aligned, the measured level is -11.63 dBm, so the filter is aligned 5dB before the compression point. The firmware searches for the peak, then the two points at -3dB. The filter is readjusted in width to have a value within the specifications, then switches to linear mode for the level adjusted to -20dBm. With your 8591E, the level reaches -4.74dBm, it's high, but it seems that the filter is reaching an alignment. Starting check 1.06MHz tests#1 560kHz tests#1 780kHz tests#1 880kHz tests#1 960kHz tests#1 1.01MHz goes to LIN mode for the level at -20dBm So, the level at 21.4MHz would be stronger on your Spectrum, as well as the limiting point since you have -4.74dBm, without knowing where the real limiting level is. ? So, as you pointed out, is this an imbalance between LIN and LOG MODE. You start from -4.74dBm to -20dBm, or 15.3dB. But on my Spectrum, I go from -11.63 to -20dBm or 8.4dB. ? But there is no error message, and you are left with an error of 15dB after the SELFCAL, while in my case everything is correct with a level of -20dBm as expected. ? ? ? ? ? ? Here are the measurements from the input to the AUX IF, and AUX VIDEO signal for all filters passing through A14 or option 130. I made a gain calculation between AUX IF and the input which is actually -20dBm. ? With AMP CORR ON, there is 24dB between the display and the measurement at AUX IF, 34dB for option 130. ? If AMP CORR = OFF, I still have 24 dB, but 28dB for option 130. ? This would mean that the correction applied is in the A12 stage, before the LOG amp. Maybe the error comes from there, the correction would not be applied correctly? Maybe the control signals should be measured on A12. ? I will check all these controls and see the behavior between CORR ON and OFF ? Yves |
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Re: Fan replacement in general Which type(s) to choose?
Before retiring from HP, choosing a fan type was handled by the Mechanical folks (I wrote firmware to manage fan speeds and cooling).
However, I can say that Nidec was a brand that we used a lot in "enterprise" computer storage equipment.
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Pete
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Re: Troubleshooting a 8591e with opt 130
Yves,
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In the meantime did some additional checking. I figured the biggest difference seemed to be in the TP1 temperature voltage.
I did a simulation of the circuitry but both our tp1 voltages seem to be reasonable. The main influence on the voltage level is the IVT potentiometer, R88. This one is glued to R33 on my board with some grey gunk. So I can't check if the value is reasonable compared to the pot setting. I didn't see any glue on your board, wondering if that was done in the factory.
Does look somebody has been fiddling with the potmeters in the past:
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After checking TP5 I figured the next interesting point might be J1 which has the output signal of the log amplifier board
The output ratio seems to be slightly off from TP5, being 17dB.?
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During these measurements I found something which surprised me. To measure the signal I removed the cable from the Log amp to the Opt 130 and connected the TinySa to J1 of the Log amp, as expected the signal on the 8591E disappeared. When I reduced the RBW to below 1khz, the signal reappeared on the 8591e. Note, the jumper wasn't placed on the LogAmp.?
I was expecting the signal always to come from the logamp to opt130 but on futher check of the schematics it seems the AUX IF is used to feed the signal to the opt130. There is no schematic of the 130 in the CLIP sadly.
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I also spent some time whipping up a python script together with ChatGPT to render the rs232 HPGL output, getting there, just some issues remaining with the select indicators under the labels in the right side menu. If there is any interest for this script in the group i'll gladly share it
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Marco
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Re: 6632B supply stuck in PROT mode, unable to reset.
Hi there;
Bad proactice to connect a battery to a linear PSU without consideration for reverse current and damage. We use series power R and diodes. I do not have 6632B but have many similar HP . Most have reverse protection doides (series and shunt) on the outputs. Also some have extenal rear panel overvoltage prot (OVP) crowbars. Check the schematic for your model and SN, one or more protection diodes may be shorted. Bon chance Jon |
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6632B supply stuck in PROT mode, unable to reset.
Hello all¡ You guys have always had the experience to assist. After years of service, my 6632B Serial number: US36351432 version: A3 from PCB, has failed. Here are some details. I was testing/charging a 14.8v LiPo and I don¡¯t recall where the voltage was set on the supply when I connected it to the battery, it may have been lower than 14.8 volts if that is important. However, when I connected it, it showed a small spark and the display went to; Voltage=0.291, and Current -0.2677 (note the minus sign), and CC.? Then the PROT notice lit up. I am unable to reset the PROT with the ¡®PROT CLEAR¡¯ button. At least I believe that is the order in which everything appeared on the display. There is no ERR showing. Upon reboot, it boots fine, and clears the digits to zero, then the 291 and 2677 come up and the ¡®PROT¡¯ lights up along with CC. The light ¡®PROT¡¯ does not clear with hitting the blue ¡®Function¡¯ button and ¡®Prot Clear¡¯ button. I don¡¯t know if the 0.291 volts, and -0.2677 is significant or not but it comes up after every reboot (On/Off cycle). Before I start digging into this, I wanted to run it by anyone with experience with this supply, I'd like to hear any thoughts. Regards, ~AF7U |
Jinxie
Electro4lease
saipan59 (Pete)
Froggie the Gremlin
Michael - AF7U