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Author Topic: Distortion on Signal  (Read 1263 times)
N7GCO
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Posts: 146




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« on: September 15, 2012, 08:52:25 PM »

Tonight I was told by a couple of people my signal was badly distorted on 80 meters. That has never happened before, in fact I usually get complements.

I did change antenna's from a 40/80 dipole to a 80 meter dipole. Since nothing else has changed, I assume it is related to the antenna some way.
I have checked all the coax and it tests fine.
My first assumption is I need to add a balun to coax coming from this antenna. I presume I would add it just before the coax enters the shack.

Any suggestions on how to trouble shoot this and get my signal clean again?

Thanks
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K2OWK
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Posts: 1065




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« Reply #1 on: September 15, 2012, 08:59:58 PM »

What is a distorted signal? I am making an assumption that it was the audio that was distorted. I do not know how the antenna can affect the audio. More information is needed for this.

73s

K2OWK
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N7GCO
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Posts: 146




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« Reply #2 on: September 15, 2012, 09:12:14 PM »

Yes, is was my audio they said was distorted. They were having trouble hearing me because of the distortion. I am running an Icom 7600 through an Icom PW-1 amp. My 80 meter dipole is hung between two tress about 75 feet high.

I was not having distortion on 15, 20 and 40 meter through my SteppIR antenna.
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K6AER
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Posts: 3524




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« Reply #3 on: September 15, 2012, 09:26:46 PM »

There is a very good chance your distortion is RF getting onto the microphone audio. Turn off the amplifier to see if the distortion is reduced. Proximity of the antenn to the station is most likely the problem. If the antenna cannot be moved further away from the station try some snap on RF beads on the microphone cord. Also check the microphone shield is connected to the radio chassis.
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KA4POL
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Posts: 2028




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« Reply #4 on: September 15, 2012, 10:11:35 PM »

You  might have common mode currents. A choke on the coax at the feed point would prevent that.
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G3RZP
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Posts: 4713




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« Reply #5 on: September 16, 2012, 12:16:14 AM »

If, as it appears, you are feeding the dipole with coax, the balun needs to be up at the dipole feedpoint, not where the feeder enters the shack.
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VA7CPC
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Posts: 2392




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« Reply #6 on: September 16, 2012, 05:38:25 AM »

Yes, is was my audio they said was distorted. They were having trouble hearing me because of the distortion. I am running an Icom 7600 through an Icom PW-1 amp. My 80 meter dipole is hung between two tress about 75 feet high.

I was not having distortion on 15, 20 and 40 meter through my SteppIR antenna.

I'll bet that K6AER has the right approach.  1 KW of RF can put substantial voltages on your mic-to-rig cable.  A balun at the antenna feedpoint, _and_ ferrites on both ends of the mic cable, should help.

         Charles
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WA3SKN
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Posts: 5494




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« Reply #7 on: September 17, 2012, 01:04:09 PM »

You are probably getting RF back into the radio.  So the first thing is how does it sound when transmitting into a dummy load?  Just listen to another radio while testing and you will know soon enough.  If it sounds clean into the dummy, you can then start the isolation process of shielding and filtering.
73s.

-Mike.
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W4VR
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« Reply #8 on: September 17, 2012, 05:49:39 PM »

sounds to me like rf in the shack.  btw, i also use a 7600 and pw1, and my antennas are far removed from the shack.
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KB5UBI
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Posts: 97




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« Reply #9 on: September 17, 2012, 06:04:58 PM »

80 meters is the clue. It's RF getting into the mic.
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