Hello, I recently bought an 8593A SA. When testing the tracking generator, I found that the LO is riding on top of the tracking generator output. For instance, when setting frequency to zero-span and 100 MHz, the TG outputs the 100 MHz and a 3.9214 GHz + 100 MHz = 4.0214 GHz signal. When setting zero-span frequency to 200 MHz, I get 4.1214 GHz and 100 MHz out, etc.
I took the tracking generator apart and all the little micro-modules looked ok. The signal path goes mixer -> passive filter -> output amplifier. All look okay. The filter is passive so cannot be broken. I verified that with the 600 MHz disconnected from the A3A15 module, the 100 MHz signal disappeared but the 4.0214 GHz signal remained with unchanged amplitude. So, it seems the A3A15 lets through the LO, 20 dBm lower (-30dBm) than the TG output (-10dBm).
I could confirm that the tracking generator (in full span) is level within 2dB across the full 2.9 GHz span. So it seems otherwise be fine.
My question is: is it normal to have the LO riding on the 8593A TG output? When measuring filters and feeding back the filter output to the 8593A input, the LO will not be visible as the maximum TG frequency is 2.9GHz. Perhaps this is by design? I find it odd, however, as my 8590B outputs a clean 100 MHz for the same test scenario.
Select pictures attached.
Thanks,
/John.