I think that basically is the problem.

Because the impedance is not set up properly on the cavities (the pass
plunger is a little off the correct impedance), then the preamp is operating
with a non-optimal impedance.

Desensing the preamp reduces the gain so reduces the amount of noise the
preamp is generating.


Sounds like a little lesson well learnt to me. Now on to returning the
cavities up properly.....;


Thanks all,

Sam

"K7ITM" wrote in message
oups.com...
It's important to realize that the optimum match for noise is in
general NOT the same as matching the impedance seen at the FET input.
The optimum impedance to match to is the FET's input-referred noise
voltage at the frequency of interest, divided by the corresponding
noise current. RF transistor data sheets will often list the impedance
for optimum noise figure. The difference between impedance matching
for maximum power transfer and lowest noise figure can be significant.
This is true with both bipolars and FETs.

Not sure what's going on with the change in noise as the repeater keys
up. Any chance some of the xmt RF is being rectified and changing the
bias on the preamp?

Cheers,
Tom