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Author Topic: Rf on audio  (Read 194 times)

W3BJ

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Rf on audio
« on: November 06, 2022, 09:31:06 AM »

I got a little rf on my audio. Running FT 710 with RE 27 and a Alpha 8410. Reports say with Amp running a little rf on audio. Turn the amp off and it’s gone. I moved the amp about 4 ft away, still there. Not bad, but there. I was wondering about ferrite cores and beads to clamp on and where to put them. Running a G5RV for antenna. Any thing will be helpful.
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K6AER

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Re: Rf on audio
« Reply #1 on: November 06, 2022, 09:49:33 AM »

How far is the antenna from your shack?


Placing RF beads on the microphone cable will generally cure the problem but this is nothing more then a RF exposure exceeding the shielding capabilities of the audio microphone path.


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W0CKI

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Re: Rf on audio
« Reply #2 on: November 06, 2022, 09:53:56 AM »

Based on my experience, individual ferrite cores and beads are not likely to solve your problem. I completely solved a similar issue by adding a common mode choke at the feedpoint of my vertical antenna. I never had an issue with my G5RV. YMMV.
Gary W0CKI
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W3BJ

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Re: Rf on audio
« Reply #3 on: November 06, 2022, 10:21:16 AM »

Antenna is 50 feet from shack. Any suggestions on line isolators or ferrite cores.?
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W9IQ

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Re: Rf on audio
« Reply #4 on: November 06, 2022, 10:45:24 AM »

Antenna is 50 feet from shack. Any suggestions on line isolators or ferrite cores.?

This is a chart for making the best possible single core HF choke. The objective to is obtain the highest RS possible for your bands of interest.

- Glenn W9IQ

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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

W6QW

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Re: Rf on audio
« Reply #5 on: November 07, 2022, 12:24:47 PM »

Antenna is 50 feet from shack....

A quick-and-dirty trick to help mitigate a possible hot chassis situation is to simply install a quarter-wavelength radial at the amplifier chassis for each band where the RF is migrating into your xmit audio.  This may enough to temporarily fix your RFI situation by creating a RF voltage node at the chassis point.  A common mode choke is preferable, assuming that's the root cause, but the quarter wave radial method could be a temporary solution.
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W3BJ

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Re: Rf on audio
« Reply #6 on: November 08, 2022, 12:33:10 PM »

Well, I have a 3 element 40m with no rf. It’s only G5RV that’s a problem. I now have a line isolators on the feed. Here’s hoping
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WA3SKN

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Re: Rf on audio
« Reply #7 on: November 08, 2022, 03:06:03 PM »

OK, a little "RF in the shack" getting into to mic audio.
My first step would be getting a .1 to .01uf cap across pin 4 and 5 at the mic input of the radio.  Pin count is 1-8 decending on the 8p8c input jack and a simple adapter could be made with the cap inside.  The mic is 600 ohm dynamic, by the way.
Next would be ferrites on the mic cable.
Of course, you could move the antenna farther from the shack... but that's work!

-Mike.
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AI5BC

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Re: Rf on audio
« Reply #8 on: December 15, 2022, 07:46:54 PM »

Check your DC power supply out. Disconnect it from everything, get yourself an ohmmeter, and measure for continuity between the negative output terminal and the AC power cord ground pin or the chassis.

If you see continuity, fix it and most likely fix your problem. Astron is notorious for bonding the negative output to the chassis. Fix the root cause of the problem rather than trying to treat the symptom with mediocre results at best.

 
« Last Edit: December 15, 2022, 07:52:53 PM by AI5BC »
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