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RF Problem - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement

Post subject: RF Problem Posted: Mon Aug 01, 2005 5:51 pm


Joined: Mon Aug 01, 2005 5:29 pm
Posts: 1
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?

Michael Valfre
Vandenberg AFB


Post subject: RF ckt behaviorPosted: Sat Aug 06, 2005 11:19 am
What 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 test.

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, a ...?

Good luck!

Posted  11/12/2012

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