R&S FSH6 Calibration

[zitt]

I just bought a "bargain basement" FSH6 to use on my bench. I've been actually watching for a "deal" on a Rigol SSA... but this deal kinda fell in my lap.

The unit had a broken front plastic bezel which I'm trying to get a spare part from R&S. Other than that; the listing said:

Powers On and works except it fails frequency response around 4.1-4.5 GHz  displaying a signal that is approximately 1.5 dB low.

I don't think I have a signal gen that will operate anywhere near that frequency.

Does anyone have some experience they can share for this noob? Since the unit doesn't have a tracking generator; is there anything I can do in my home lab to repeat the test to verify it is indeed low?

Extra Credit: Can I then fix this frequency error thru calibration? Or will it require a repair?

I have one out of 3-4 "calibation houses" that said:

we’re confident it can be repaired to correct the issue or defect you’ve described

  then quoting an 85/hr and saying most are repaired within 5 hours.  I'm not against paying 425 to have it repaired... but I don't want to give them that kind of cash if this is a simple fix.

Advice?