10 GHz strange self-oscillation in DEMI transvert TXS-2000X

[jracepilot]

Did you ever figure out what was wrong?

[lustrup]

Yes. I did.....It was the built in +12V to -5V converter oscilator coil inverter. It was drifting in frequency and had lots of overtones / harmonics and reacting to the magnetic influence of Earth when it was moved around. The 144 MHz IF out /input plugg was very close to the inverter. By shielding the coaxplugg inside the interferince whent away.

[jracepilot]

Wow, that IS a weird one!! I'll have to file that one away in the back of my mind, just in case I ever run into that. I have the low power version (10 mW) and the external 3W amp, so the offending circuit is inside the amp case, so I may never notice that particular problem. Thanks for the note!! Scott N0EDV.

[lustrup]

Ok Scott....I first noticed the problem when monitoring a weak beacon over many hours on Spectran display. It took me 1/2 year to find the problem, with fruitless numerus telefoncall to DEMI. I tried to bypass all mmic's even put in 3dB pads between stages to no help. Then just by accedent I put my screwdriver close to the inverter and the ofending frequency changed everytime the screwdriver was close to it.

[synthesizerman]

Danger Death Ray