Matt, what I have noticed is that for certain settings mine sometimes freezes and then I have to give a master reset. I think that this has to do with incorrect power levels (calibration). Jeremey also mentioned that strange behaviour can happen if the calibration is incorrect.
This weekend I have measured the conversion loss of the fist down converter and it was about 11 dB ( -20 dBm Cal and 0 dB ATT -> -31 dBm at IF1 2.05 GHz). Next I have terminated the IF1 and started to investigated the RF block for my old gain loss problem. When I connected it all together I noticed that the frontend was deaf. I suspect that the first mixer is broken and I do not know how this could happen. I’m pretty precise and have more than 30 years’ experience in RF/Microwave
. I have remeasured the IF1 gain block and checked the LO power again and it was fine, +21 dBm.
For the RF block I have checked voltages of gain stages, switching of R.B.W. BPF (1.5 MHz and <300 kHz), RF level adjustment (cal. screw on the front) and some LO sources if possible. For the RF gain level adjustment I have noticed that according the schematic it should be 5.5 V ± 3.5 V and I have measure 2.22 – 6.12 V. May be it is limited on the frontside board but I did not check this.
I was not able to checked the power levels at the RF part because I do not have a RF probe. Unfortunately there are no interfaces where you can measure it unless you cut the circuit. A second thing what I have noticed is that the 1.84 GHz LO power out of the RF block going to the TG is less than the 8 dBm which is mentioned in the schematic. This signal is also going to the 2nd mixer (amplified). I have measured the power at the output of the 1.84 GHz B.P.F. which is a separate block outside the RF block, connected with semi-rigid. I have measured about 0 dBm at the BPF output and the loss of the filter is 4 dB which means that out of the RF block it is about 4 dBm. Matt are you able to measure this for comparison.
Summarised, one step forward and two steps back
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73, Lex