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RF In My Audio

Raccoon

Raccoon

Well-Known Member
Oct 27, 2005
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Hi everyone , I just tried to check into a Net on 40 meters and the Net controller told me that he was hearing some RF in my audio . What I was wondering is, exactly what kind of damage can your radios get from keying up with RF in your audio ?

Keep in mind that, no I'm not going to keep trying to talk on my radio until "AFTER" the RF issue is fixed ... and no, I haven't already talked on it a hundred times with it having this issue . I was just wondering what kind damage radios can get from keying up on them with RF in your audio.
 
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Could be he was pulling your leg, your signal has RF in it being composed of a RF carrier. Now, RF in your audio is a different story. We're you using sideband or fm?
 
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Understood, I have never seen that type of damage from RF creeping into the mic or mic/modulator circuit. Is this a new install? Or did this just happen while it was working normally before? I'd check your grounding, jumpers, mic wiring and antenna placement. What model radio, what mode, what mic, and are you running much power?
 
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Isn't RF required to have audio? Did the other station possibly mean you had "crunchy" audio? If so that could be nothing more than too much mic gain/ audio compression.

What antenna are you using? Coax feedline? How far from shack? How much power? Common Mode choke at antenna feedpoint? Correct grounding? Are you getting bit from the mic or by touching the radio when transmitting? Unusually high noise levels on RX?

Many times, if you actually do have a problem, it originates with excessive common mode current on the outside of the coax shield due to an imbalance of current at the antenna feedpoint.

7 3
 
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Signal rectification is what the hams call RF getting into your mike or the radio's mike jack. Tends to cause muffling or garbling distortion to the voice audio.

Might be what he meant. Might just be what he thinks he's hearing.

I was a naughty boy one night playing with a web SDR while tuning in the same roundtable conversation on my TS940. Chose one guy in the group who was fairly strong on the web SDR and keyed my mike while he talked. The SDR latency created an echo effect since the other guys couldn't tell my echo signal apart from his direct audio. He got all kinds of bogus advice about what might be wrong, along with "RF in your mike" kinds of diagnosis. I came in at the tail end of their fun and before long they all signed for the night.

Haven't pulled that prank since, not even once.

73
 
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To answer a few questions. I was talking on my Yaesu FT-757GXII , using it's stock mic , with a Carolina Windom antenna. I am using a LDG Z-11 Pro automatic antenna tuner, so I shouldn't be having any SWR problems. I was on LSB talking on a 40 meter net. But checking out my coax I found a few cracks in the coax casing, so I'm assuming that this is the culprit for the RF in my audio. I was just wondering if anyone might know what kind of damage a radio could get from transmitting with RF in their audio.
 
Raccoon said:
with a Carolina Windom antenna.
Click to expand...
Do you have a separate CMC choke in your feedline, in addition to your 4:1 transformer?

Your tuner will not prevent common mode on your coax that can radiate and cause possible issues in the shack. Cracks in the outer jacket of your coax will not cause common mode issues but will allow water/moisture entry obviously, never a good thing.

7 3
 
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Crawdad said:
Do you have a separate CMC choke in your feedline, in addition to your 4:1 transformer?

Your tuner will not prevent common mode on your coax that can radiate and cause possible issues in the shack. Cracks in the outer jacket of your coax will not cause common mode issues but will allow water/moisture entry obviously, never a good thing.

7 3
Click to expand...
I guess that my confusion is coming from the fact that I've been using this same coax and antenna for at least 10/12 years without any issues. And now all of a sudden I'm being told that I have RF in my audio. I'm always on 40 meters, and on LSB , but I've tried different radios with the same result.

Would updating my coax solve the issue , or is it still going to be there
 
Maybe your audio is perfectly fine? One of the best ways to hear your TX audio is with another radio with headphones and no antenna. Whenever I get a new radio, I go through my microphone collection to see what sounds the best. Great for setting microphone level and even modulation. I do a quick check every time I power up, just to make sure nothing changed or got bumped.

Using this method, you can tell if you fixed it or made it worse. Or maybe it's not even an audio problem.

Ps. I don't think rf in the audio would really hurt anything. Your microphone might bite your lip though.
 
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well i would say the most likely culprit is the radio itself.
it's got to be at least 30 years old at this point. it's not unheard of for a radio to start having strange issues after being "alive" this long.

do you have another radio you can try in order to eliminate the rest of your equipment chain as possible culprits?
LC
 
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Told to the mechanic:

"It started up and took me to work every morning for 30 years. Now it's got a funny noise in the motor and misfires. Can't be much."

Sounds more like RF riding on the outside of the coax braid. All the RF current in the coax should ride on the inside surface of the shield braid. If one condition or another causes the coax to become an antenna element, there will be RF current flowing on the outside of the shield. That will carry RF into the house, and the radio's metal cabinet will be hot with RF. Choking this RF current with ferrite over the outside of the coax often helps.

Why it didn't do this until now is the open question, as much as why it's doing this at all.

73


73
 
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loosecannon said:
well i would say the most likely culprit is the radio itself.
it's got to be at least 30 years old at this point. it's not unheard of for a radio to start having strange issues after being "alive" this long.

do you have another radio you can try in order to eliminate the rest of your equipment chain as possible culprits?
LC
Click to expand...

I've finally tracked down the culprit , it wasn't the radio or the coax . It was the MH-1B8 stock mic . I went with Shadetree's advice , hooked my dummy load up to FT-757GXII , and listened on my FT-897D using my headphones ... and my MH-1B8 stock mic had dirty contacts . When I bought the radio at a local ham fest last year, it didn't come with a mic . So I looked online and found an MH-1B8 stock mic that was still new in the box , never used ... and I bought it . Listening with my headphones I could hear that it wasn't getting a solid keyup, cutting in and out and sounding all wonkie ... cleaned the contacts in the mic , and now it's fine . I did have to readjust the mic gain , and the ALC because that was a bit higher than it should have been too . So I'm sure that wasn't helping matters any either.

Thanks everyone for all the advice and help, I appreciate it all .
 
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