Rohde & Schwarz FSH Series - Any techs that work or have worked on these?

[scopeman]

I have a couple of R&S FSH series analyzers that have issues with the signal level display. At first I thought that the attenuator IC was defective but it turns out not to be the case. If I input a known signal level (say 10MHz at -30dBm) and manually move the reference level so that the RF attenuator steps  thru 0,10,20,30 dB the indicated level at 0dB will be 5dBm high, at 10dB about 0.85dB low, at 20dB about 8dB low and at 30dB about 12dB low. Furthermore this level discrepancy does not change with frequency. Now if I set the RF source to match the reference level and then reduce the RF source in 10dB steps the display tracks perfectly. It does the same for 2dB steps as well. So it looks like the log amp (or the software that emulates one) is working correctlty.

The sensitivity appears nominal. So it looks to me to be a calibration issue, or something really strange going on with the stepping of the RF attenuator IC which has been replaced and its tracking appears to be the same as the old one. When I replaced the IC I did not see anything unusual on the PCB. It looks clean with no evidence of overloading, etc.

Has anyone been able to figure out how to calibrate one of these? Perhaps its just a look up table somewhere but I don't know. If I were to send it to R&S they charge more than it's worth just to cal it and if they can't cal it they still charge a small fortune.

I really would like to get this one working as it has a tracking generator and I have the reflection bridge that goes with it.

Thank you for any help you can render.

Sam
W3OHM

P.S. I have heard that there is software out there to do a level cal but I have been looking for quite some time and have never found it.