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| Agilent E7495 linux root account |
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| 9aplus:
@ddcc Thank You for that picture, during my unit PS repair I was wondering what is inside that box :popcorn: Member here Wolfgang made nice FET probe which can be of good use during your repair -> https://electronicprojectsforfun.wordpress.com/2018/08/03/a-homebrew-fet-probe-to-1-5ghz/ Good luck with the rest of your repair journey. |
| ddcc:
--- Quote from: 9aplus on March 24, 2019, 07:59:03 am ---Member here Wolfgang made nice FET probe which can be of good use during your repair -> https://electronicprojectsforfun.wordpress.com/2018/08/03/a-homebrew-fet-probe-to-1-5ghz/ --- End quote --- Thanks for the link, looks useful! --- Quote from: PA0PBZ on March 24, 2019, 07:57:44 am ---This is the block diagram of the RF part for the N1996A, the bigger brother. It could help because they are very similar. --- End quote --- Thanks, I saw the reference to the N1996A earlier in the thread. Some parts are a bit similar; e.g. the four 1st LO filter banks, and two mixers for the 1st and 2nd converters. But otherwise, a lot seems to be different; for example, there doesn't seem to be a 3rd converter, the LO/IF frequencies are different, the attenuator values/positions are different, and the intermediate filters also seem different, although most aren't labeled on the PCB. I'm also not sure why there's a 2.7 - 4 GHz high band on the E7495A, since the instrument is only rated up to 2.7 GHz. |
| Wallace Gasiewicz:
Has anyone resolved the GPS lock issue where the yellow triangle stays on and there is no green "lock" on the time/frequency base? Wally |
| technogeeky:
--- Quote from: ddcc on March 24, 2019, 06:15:06 am ---So it turns out that on my unit, the spectrum analyzer, signal generator, and two-port insertion loss features seem to work fine, but the one-port insertion loss and return loss measurements give incorrect results. Since there's no block diagram available, I ended up taking apart and reverse engineering the receiver board, shown below. I don't have much previous RF experience, so corrections/suggestions are welcome! It seems that this unit is a superheterodyne receiver using double conversion, with the 1st LO at 1.5 - 3 GHz, the 2nd LO at ~3 GHz, and a final IF at ~135 MHz. The unit seems to have two separate receiver bands, one for < 2.7 GHz, and the other for 2.7 - 4 GHz ??. There are 2x 5-bit (<= 31 dBm) digital attenuators on the input path, and a 0 - 90 dBm electronic attenuator on the output, although the module seems capable of up to 130 dbm attenuation. Since this unit is designed for portable operation, the internal cables are short and the assemblies are all stacked on top of one another, making it difficult to probe the receiver board with the unit running. I ended up removing the connection panel and flipping the receiver board, which gave me access to its top side. Since the spectrum analyzer and signal generator features work independently, I'm guessing that the fault probably lies on the feedback path from the source output on to the input path, which runs from the coupler through some filters and SPDT switches (from D to A on the annotated image). Interestingly enough, some rework seems to have already been performed on the filters on this path, probably by the factory? Next, I plan to probe this path while operating the unit in return loss mode, but this will be a bit tricky because I only have a 100 MHz scope, and no other spectrum analyzers or high-frequency probes. However, I do have a RTL-SDR and a LimeSDR, so I can probably make do, and just need to compile the software stack on my laptop. --- End quote --- Thanks for posting this. I've been waiting a long time to see this (since my unit doesn't have problems, I didn't want to open it). Can we also get the same picture without annotations -- for A/B comparison to see your notes? Also, can we get some shots from a low angle (say, 30 degrees up from the plane of the board) so we can see the size and configuration of RF gaskets and such. Thanks! |
| technogeeky:
--- Quote from: ddcc on March 24, 2019, 06:15:06 am ---So it turns out that on my unit ... Interestingly enough, some rework seems to have already been performed on the filters on this path, probably by the factory? --- End quote --- I'm like you and I don't have much RF experience, my initial reaction to looking at this picture carefully is that I would be surprised that this is factory rework. Upon reading your comment and looking at the path involved (along with your statements about what works and what doesn't), I think we have a repair attempt. It looks like all of the reworked items are passives, too. My first guess would be to check the SPDT switch that comes out on the right side of the board at A. :-// |
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