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HP8590L replacement of original YIG with a different model

Question asked by Sputnik on Sep 28, 2018
Latest reply on Nov 9, 2018 by dhamilton

The original YIG (2.0 - 4.0 Ghz) doesn't deliver enough output. I sourced for an alternative YIG that should be a close match (5086-7259 YIG Oscillator: 2.0-4.5 GHz, 15-18 dBm). When I attach my simple RF amp. meter it shows +5db which is still 10db lower then I hoped for but I continued to make the connections.
I used external power supplies as the voltages differ from the original one (+20v, -10v). My first question would be if it is save to use the analyzers power rail from -5v to +15v to come up with the required +20v without the risk of running into some ground loops?
The required current to control the frequency is different from the original one, I placed a resistor in parallel to the main coil to shift the frequency downwards and it seems to work. I see on the analyzer screen (using int. ref. signal of 300Mhz, -20db) a -29db signal which is out of frequency. I can shift the peak to the right place (e.g.300Mhz) but when I change the centre frequency of the analyzer it is out again and requires again manual interference on the parallel resistor.
I see no difference when I connect or disconnect the FM coil (and I am not sure if I choose the right connection), can somebody elaborate how I could best test the function of FM coil ?
Another problem is, when I cross from SPAN 10Mhz to below 10Mhz, below I see only a flat line :-(


So in summery I conclude that the YIG is oscillating, the frequency is not always in the right place and the PLL seems to be unable to control it. The output level seems 10db too low (not sure if that is a big problem as the calibration might be able to compensate for that ?). The FM coil doesn't work yet
Any suggestion from somebody who did conversion work in that manner id highly appreciated !!