Agilent E4432B ESG-D signal generator I/Q output - Page 1
Forum section: electronics / testgear

author: ltarjanyi75
author_rank: Contributor
timestamp: March 02, 2025, 01:48:42 pm
content: Hello!I recently bought a E4432B signal generator with Dual Arbitrary waveform generator (Option UND).I am learning to use it and playing around with arb waveforms and IQ modulation.According to its programming manual it should give out voltages based on data in waveform like below:"Bit-value-versus-output-power:• 0 gives negative full-scale output• 8192 gives 0V output• 16383 gives positive full-scale output"When I send the exact same binary file both as I and Q data and look at the I and Q outputs on the back of the device with scope, the Q output corresponds to the documentation above, but the I values are inverted. I output gives negative full scale at 16383 and positive full scale output at 0.I am totally confused with this behaviour.Could someone help and shed some light on this?Thanks,Laszlo

author: ltarjanyi75
author_rank: Contributor
timestamp: March 23, 2025, 11:12:02 am
content: Hello!Noone could help with any idea? Just trying one more time...Thanks!

author: G0HZU
author_rank: Super Contributor
timestamp: March 23, 2025, 09:11:35 pm
content: Give me a day or so and I'll set my E4433B up for IQ data transfer.I haven't done this for a while with the E4433B. I recall that I use the PSG/ESG toolbar in Excel to do this although there are several standalone exe files from HPAK that can also do this. I do recall having issues with some of them and I always ended up going back to the excel toolbar as it was the most reliable.I think the E4433B can accept 16 bit files and it converts them to 14 bit so maybe also try this? I always found this aspect of the E4433B to be a bit flakey. Also my E4433B has had to have two SRAM chips replaced in the UND module because it started giving erratic outputs. It would be OK for maybe 2 minutes and then it would start sending out corrupted data. However, since replacing two of the SRAM chips it has been fine. I think the SRAM failures in the UND card are quite well known about online.For a few years I used the E4433B a lot for stuff like this. I would capture data with an RTSA and then convert it to the 14 bit format for the E4433B. I then loaded it into the E4433B via GPIB as I and Q files. This did work really well but only if I used the Excel toolbar from HPAK and even this only worked properly on a couple of laptops.

author: G0HZU
author_rank: Super Contributor
timestamp: March 23, 2025, 10:30:45 pm
content: I've done some initial tests, first on my E4438C sig gen. This is the one I use the most for vector based stuff these days. I've got half a dozen vector sig gens here and the E4433B rarely gets used for this stuff now.I renamed a simple (two tone) I wavefile to Q so I then had an identical I and Q file in 14 bit format. I sent this to the E4438C first as it is already set up for this stuff. I found that the I and Q output waveforms at the rear of the E4438C were the same and they were in phase when viewed on a scope.I then tried this with the E4433B expecting to see the same but I got the same result as you did. The I and Q outputs are in anti-phase. I'll have to think about this to see how significant it is...In the past I have used the E4433B as the master vector sig gen and connected the I and Q outputs to the I and Q inputs of other vector sig gens and they appeared OK on the other sig gens. I've only ever done this with relatively simple waveforms though. Maybe I missed something here all along and there is a bug.I've got some more I and Q files I can send to the E4433B to explore this issue a bit further.

author: G0HZU
author_rank: Super Contributor
timestamp: March 23, 2025, 10:43:16 pm
content: The same thing happens if I send a single 16 bit bin file version of the same waveform to the E4438C and the E4433B. The E4438C produces the expected I and Q waveforms but the E4433B has one output inverted.

author: G0HZU
author_rank: Super Contributor
timestamp: March 24, 2025, 10:58:49 am
content: This has jogged a few memories now... On my old notes for applying external I and Q to my Aeroflex IFR vector sig gens (I have several of these) I have written down 'swap external I and Q'.However, I now think this is wrong. The problem is with the E4433B I and Q outputs and it isn't that the I and Q are swapped. One of the outputs is inverted as you have discovered. However, swapping I and Q must have worked for me with the IFR sig gens. I would have used fairly simple waveforms though.Mainly noise and multi-tone waveforms but I also used to use these sig gens to generate USB and LSB to test comms receivers. I generated I and Q files for USB and LSB containing my voice (counting to ten) and I used to generate these with the E4433B and then use the IFR sig gens via external IQ. The quality of the vector modulator and the linearity of the PA stages in the IFR sig gens is much better than the E4433B and that is why I used to do it this way. The IFR generators produce less spectral spreading than the E4433B.I recall that the E4433B would generate the USB correctly (with my voice) at its own RF output but the IFR sig gens would produce LSB with external IQ driven from the E4433B. So I swapped the I and Q inputs to achieve USB and I assumed something was backwards in the IFR sig gens. But it may have been due to the issue that you have discovered.Thanks for doing this and posting it on here. I'm not sure what the fix will be to this bug. I doubt Keysight will do anything about it as these generators are really old.

author: G0HZU
author_rank: Super Contributor
timestamp: March 24, 2025, 01:23:41 pm
content: Here's a screenshot from my old IQ viewer program.This imports data from the Keysight 89600 software in one of its BIN formats (after importing .MAT data into the 89600 SW from an RTSA) and allows me to view the IQ waveforms. It lets me add trigger events with a mouse and also crop out shorter sections from much larger captures and then this format (that suits the E4438C) can be converted by the viewer program to the 14 bit format for the E4433B and then loaded into the E4433B. It also supports the E4438C but without triggers. It also allows the data at each sample point to be clicked on with the mouse.The main use for this was for reverse engineering certain types of digital modulation for a project at work. It allowed me to recreate offair signals using the E4433B (that were initially captured with an RTSA) and I could crop out (and play back on repeat) the most interesting parts of the signal.I also added an IQ flip feature to it. The aim here was to be able to generate an LSB IQ file from a USB capture. So I only had to do one capture of my voice with an RTSA to get both LSB and USB. However, I think I abandoned this part way through writing the code for it. I don't think I could get it to work correctly without adding some additional spectral artefacts.One option for you is to do something similar in something like Excel and then deliberately invert the I data before loading it into the E4433B. At least this would generate the correct IQ at the rear of the instrument. The main RF output would then be flipped though. It depends what you want to do with the E4433B IQ outputs.

author: ltarjanyi75
author_rank: Contributor
timestamp: March 24, 2025, 07:20:57 pm
content: Hello G0HZU!Thank you for your thorough testing and description you gave!If I understand you correctly, the IQ data I load to the siggen generates the correct RF output and the inversion probably only occurs at the external I and Q output.So I have to watch out and do conversion of the data if I would like to use the output connectors with some other signal generators input.I tested the RF output by playing an AM music sample converted to I and Q data (loaded to the signal generator) and sent out on an RF carrier. I was able to receive it on a tuned SDR and it worked nicely. But maybe the AM modulation would also work with this inverted behavior... I am not sure (still learning the I and Q modulation).Btw I discovered this issue by trying to send I and Q data through serial port (with USB to Serial cable) from my notebook using python code to the device. Still have other issues with this, but throughout my tests I bumped into this "bug" also.Data download with excel/GPIB (PCI card) works fine on one of my old computers, but it is slow and cumbersome. I would like to setup an environment on my laptop with only USB port to somehow be able to download arb waveform files to the siggen.Thanks for your help once again! I know now that this is not my misunderstanding and what to watch out for!

author: G0HZU
author_rank: Super Contributor
timestamp: March 24, 2025, 09:50:26 pm
content: Quote from: ltarjanyi75 on March 24, 2025, 07:20:57 pmIt looks like that is correctAlso, on my E4433B if I set it to multitone mode and set it to output 4 tones (each spaced by 10 kHz) and then disable the tone at the lowest frequency on the E4433B and then output the waveform at the RF output port then it appears correct on a spectrum analyser with the lowest frequency tone of the four turned off. However, if at the same time I connect the I and Q outputs from the E4433B to one of the IFR sig gen I and Q inputs the waveform from the RF port of the IFR sig gen appears mirrored with the highest frequency tone (of the four tones) missing.In the past I assumed this was an issue with the IFR sig gen but it now appears to be the inversion issue you discovered with the E4433B 'I' output at the rear of the instrument.I'll do some more tests tomorrow but I also tried inverting the I data before exporting it from my IQ Viewer program and this makes the I and Q outputs appear correct at the rear panel. However, the main RF output is obviously now incorrect as it shows the effects of the inversion of I.