Agilent ESA-E E4404B 2db amplitude low error on high band (3-6.7 GHz)

[inaxeon]

Hello

I've been looking at this rather interesting problem over the last few days. If I sweep a test tone, just as it crosses 3 GHz, a 2dB fall in amplitude is observed. I checked against another analyser. It's definitely the ESA-E at fault.

I went through all of the RF performance tests outlined in the service manual. The problem appears to be at the A8A6 (RYTHM) where the IF output is -24.5 dBm with the suggested input instead of -22.5 dBm. The error is quite linear all the way through to 6.7 GHz.

Beyond this I'm unsure how to tackle it properly. I found that I can make a cheeky modification to the A8A4 (LOIS) by cutting the Pi attenuator at its output form 3dB to 1dB. Technically fixes the problem but is this really the right approach?

Has anyone seen anything like this? Are there some adjustments that could be made or perhaps do I have a faulty switch or mixer in this assembly!

Thoughts appreciated.

[inaxeon]

The other thing that has me scratching my head is that I have a further 2dB of video shift error in the high band, as in: With my "fix" I get accurate amplitude with a small span i.e. 100 MHz, but with a large span i.e. full span, I've got another 2dB of error.

How is the instrument meant to calculate and correct video shift in the high band? The 50 MHz test signal surely wouldn't be adequate for that? I can't see any mention of this in the service manual either. There must be something I'm failing to understand here...

[inaxeon]

I found this document here, which has some pages related to this (not appearing in the calibration manual):

http://www.xymox1.com/Misc/Adjustments.pdf

Under the heading "Frequency Response High Band Adjustment". It looks like how this might be able to corrected, certainly the video shift part of it. I've not yet found any detailed instructions on how to perform this procedure, even if one possessed the equipment listed.

[inaxeon]

Looks like someone has (now) covered this in this thread: https://www.eevblog.com/forum/testgear/esa-instrument-adjustments/