HP 8753C Network Analyzer A3 SOURCE problem - Page 1
Forum section: electronics / testgear

author: kada
author_rank: Contributor
timestamp: November 20, 2015, 02:59:20 pm
content: Hello dear colleagues!I have problems with my HP 8753C network analyzer. F/W version: 04.13. Options: NONEThe first problem is A3 Source. I tried to check the output regarding to "A3 SOURCE AND A11 PHASE LOCK CHECK" of Source Group Troubleshooting found in service manual.And I found out only 3.8 GHz -40 dBm signal with slightly several MHz frequency hopping at RF OUT port. This signal is independent of pretune frequency of VNA. I did not see any other harmonics except 3.8 GHz:After it I measured the signal of Cavity oscillator and got the 3.8 Ghz signal with much more power: about +10 dBm. So the Cavity oscillator is functional. Also I checked YTO oscillator and did not see any signal. I checked all power rails of YTO and they looks good. So I think the problem is defective YTO.The question is how I can test other parts of A3 SOURCE module without YTO?I tried to apply 0-3GHz 0dBm signal from generator to A3 SOURCE instead of YTO and measured signal with SA at RF OUT port of VNA. I can see the signal from generator, but there are many harmonics as well:100 MHz 0 dBm 500 MHz 0 dBm 1000 MHz 0 dBm 2000 MHz 0 dBm 3000 MHz 0 dBmIs it normal or should I see only one harmonic going from generator? As I understand it I see harmonic mixing components. Should they be filtered in the amplifier of A3?Thank you to everyone who will respond!

author: kada
author_rank: Contributor
timestamp: November 20, 2015, 06:56:32 pm
content: Maybe it can help. This is block diagram of 8753 A/B/C and 8702 A/B network analyzers:I applied the signal from signal generator to A3 SOURCE assembly instead YIG OSC at mixer input.

author: MadTux
author_rank: Frequent Contributor
timestamp: November 21, 2015, 01:42:26 am
content: What signal generator and what spectrum analyzer are you using? Is that the build in 8753C SA or some crappy external one?Seems to me that the mixer doesn't really like signals below 100MHz and that it's either some weird single sideband mixer or that the SA doesn't see signals above 3.8 Ghz.100Mhz Pic: 100Mhz pass from sig gen and 3.8 from LO, some weird signal @ 1.2GHz500Mhz Pic: 500Mhz pass from sig gen and 3.8 from LO. Low side band mixing products and 2. harmonic @ 3.3 and 2.8Ghz. Upper sideband signals are somewhat absent1000Mhz Pic:1GHz and 2. harmonic pass trough from sig gen and 3.8 from LO, Mixing products @ 2.8, 1.8, 0.8 GHz2000Mhz Pic:2Ghz from sig gen and 1.8GHz mixing product. No cavity LO visible. Funny reverse mixing product @ 200MHz from 2* Siggen x LO, some weird mixing signal I cant explain @ ca. 2.2GHzSo far that mixer looks OK to me, except I can't see the upper sideband. Probably some mixer feature or crappy SA.PS, that 150MHz/div scale is confusing as fuck

author: kada
author_rank: Contributor
timestamp: November 21, 2015, 06:21:33 am
content: Quote from: MadTux on November 21, 2015, 01:42:26 amSignal generator: HP E4433B ESG-D 4 GhzSpectrum analyzer: HP 8595E 6.5 GhzQuote from: MadTux on November 21, 2015, 01:42:26 amThe SA is operate properly.Quote from: MadTux on November 21, 2015, 01:42:26 amPlease note that SA connected to RF OUT port of VNA and not to the mixer output. Most likely the upper sideband is filtered after mixer in the A3 assembly and so we do not see it.The question is it necessary or not to filter other unwanted mixing components before the signal is applied to the DUT? I want to understand whether it is a failure of A3 assembly or it is normal?Quote from: MadTux on November 21, 2015, 01:42:26 amSorry for thatI use KE5FX GPIB Toolkit to grab data from SA via GPIB interface.And while I have not figured out how to change the scale.

author: KE5FX
author_rank: Super Contributor
timestamp: November 21, 2015, 08:25:17 pm
content: Quote from: kada on November 20, 2015, 02:59:20 pmThe YTO runs from 3.8-6.8 GHz or thereabouts, not 0-3 GHz...? Check the current through the main tuning coil. Normally it will be around 20 MHz/mA, give or take a factor of 2x depending on the YTO model. With the 8753C set for 500 MHz, for instance, you should see 4.3 GHz from the YIG with about 200 mA through the main coil.This is what it should look like at the output port with the 8753C set to 500 MHz CW sweep:Quote from: MadTux on November 21, 2015, 01:42:26 amAgreed, it can be difficult to label graphs with human-friendly scales in the general case. Try it sometime.In SSM's case, it just reads the analyzer's current span and labels it arbitrarily at five equally-spaced divisions. You can change the scale by changing the analyzer span or by editing ssm.cpp and recompiling, but that's about it.

author: kada
author_rank: Contributor
timestamp: November 22, 2015, 09:36:51 am
content: Quote from: KE5FX on November 21, 2015, 08:25:17 pmThank you very much! I mistakenly applied 0-3 GHz instead 3.8-6.8 GHz to the mixer of A3.My sig gen can output 4 GHz max, so I tried to do it.I measured signal at the RF OUT port when apply 4 GHz - 0 dBm to mixer:Cavity ocs frequency = 3.8 GHzSig gen frequency = 4 GHzRF OUT freq = 4 GHz - 3.8 GHz = 200 MHzSo mixer looks functional. But I can not test it with frequency >4 GHzI also tried to check ALC functionality of A3:By changing SOURCE POWER of VNA I can see a power changes at the SA. The power level at SA is ~2 dB lower than VNA set level.Also I tried to change sig gen output level from 0 dBm to 20 dBm and could not see any changing of RF OUT level.So I guess the ALC operates properly.I think the entire A3 assembly operates properly except YTO.Quote from: KE5FX on November 21, 2015, 08:25:17 pmThank you very much for amazing toolkit! It really makes life easier!