[G0HZU_JMR]

Sorry to drag up an old thread but in recent weeks I've been servicing both of my Advantest TR4172 analysers and I found a minor issue in the dreaded and undocumented mixer/IF interface unit.

So I spent a bit of time reverse engineering it. All my findings are subject to a degree of technical risk but if anyone wants to know about the amplifer in there or how it is biased or how the rest of the interface unit is designed (i.e. what is in there and what it does) then I can post the info up on here. I can do the same for the first mixer unit too.

Both of my analysers were showing a gradual reduction (over time) in front end linearity and a gain loss of a few dB and a slight degradation in DANL.

This analyser has a very beefy first mixer using 8 diodes (+22dBm LO drive level typical) and typically gives a mixer input IP3 of +22dBm.

But my analysers had slowly faded to giving only about +10dBm IP3 and this is down at the performance level of my old HP8568B with its very basic two diode mixer.

If I had not spotted/fixed this slow decline in gain and IP3 then the interface unit would have degraded to a point where the analyser had gone very deaf. i.e. there is an issue in this module caused by corrosion over time.

I can post up all the service/repair info if it is needed. i.e. if G4UUI and G8MUE still have their analysers stashed away as BER.