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RF Problem - RF Cafe Forums

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.

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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