Post subject: RF Problem Posted: Mon Aug 01, 2005 5:51
Joined: Mon Aug 01, 2005 5:29 pm
I need some help. I have an rf circuit that I believe
has a bad cable or connector. I have taken a Signal Generator to
one side of the circuit and a power meter to the end side. at one
end I need to see a power level at aboiut -27dBM. In order for me
to do that I have to attenuate the signal using an adjustable attenuator.
for what ever reason I can only attenuate the signal to -13dBM.
Any furthur and I lose my signal. If I take a 20dB in-line attenuator
to the end of the cable I can tune the the power level to the desired
dB(-27dBM). I even put a spectrum analyzer to the circuit and saw
the freq I need with the 20dB attenuator in line and saw the signal
perfectly. When I took the in-line attenuator out and went straight
through, the carrier fell beneath a noise floor that was not there
when the in-line attenuator in the circuit. Would this have anything
to do with a patially cut cable where there is still center conductor
continuity? Or a bad connector?
RF ckt behaviorPosted: Sat Aug 06, 2005 11:19 am
you're describing is a classic non-linear behavior. In general,
you get nonlinear behavior from active devices (like transistors
and FETs) and diodes.
You can unintentionally create a bad
diode if there's corrosion between 2 conductors carrying RF, but
it's more likely that there's a bias problem in your circuit under
You haven't given much data on what kind of circuit
you're testing, so the best I can do is the generic vague stuff
above. Is your circuit an amplifier, a variable-gain stage, a modulator,