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Author Topic: Having reports of RF getting into my audio.  (Read 1584 times)
W7QHH
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Posts: 90




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« on: January 09, 2017, 11:06:01 AM »

  I have been told that I have RF in my audio on 40 meters. I have a Heath PM-2 Field Strength meter with a 12" antenna. I'm wondering if there is a way I can make it more sensitive so I can sniff around my antenna coax, tuner, and transceiver, etc. and try to locate the source of the stray RF. Does this seem like a doable idea? All input will be greatly appreciated. Thanks 
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KE2KB
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Posts: 511




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« Reply #1 on: January 09, 2017, 11:32:18 AM »

First thing I would check is my grounding system.
What do you have for a ground on your rig?
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WB4SPT
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Posts: 432




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« Reply #2 on: January 09, 2017, 12:54:18 PM »

Take a toroid with an ID that will clear a PL259.  Wrap 8 turns of #22 insulated wire around it and attach to three feet of RG174 or RG58 or RG anything coax to your meter.  Center to the top banana, shield to a cab. screw.   Run the antenna coax (it is coax??) thru the toroid.  

How far away is the 40m antenna?

I recommend not chasing ground attachments to the radio.  You may find one to kinda work, but it will likely be freq sensitive.  Best to choke off the offensive current, and not try to shunt it into some length of copper that has dirt some distance away.  

ps:  most of this kind of work ends with buying or making a good antenna current balun. 

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W7QHH
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Posts: 90




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« Reply #3 on: January 09, 2017, 02:14:49 PM »

Thanks guys, My shack is in an upstairs bedroom. I have about a 25' run of #14 wire to an 8' ground rod. The closest point from my rig to one of the antenna legs is about 20'. Antenna is a doublet cut for 80 meters fed with open wire feeders into a 4:1 balun and on into the shack with about 12' of RG8-X into MFJ-949/E tuner with about 1' of coax to the Kenwood TS 50 transceiver. I placed a 3' whip on the Heath signal strength meter and get lots of meter deflection when getting whip near the coax, tuner or back of transceiver. What to do? Thanks again
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WB4SPT
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Posts: 432




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« Reply #4 on: January 09, 2017, 02:34:43 PM »

The toroid trick above will isolate the readings to common mode coax current, the evil one.  That 3' whip is picking up from the antenna directly at 20', I'm sure. 
Describe the 4:1 a bit more?  Voltage or current balun?
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W7QHH
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Posts: 90




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« Reply #5 on: January 09, 2017, 03:24:36 PM »

WB4SPT, Thanks, I will build the toroid unit. I have some with about a 1" hole in them, pretty heavy, not sure what mix. The 4:1 balun is a W2AU cheapie I believe, current type I think. Could I have a problem here? Also, at the point where the coax and my ground wire come through the shack wall to the exterior and the coax hooks to the balun, I could connect the shield of the coax to the ground wire making for a shorter run to the ground rod. Could doing this improve my situation? Really appreciate your help!!
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WB4SPT
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Posts: 432




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« Reply #6 on: January 09, 2017, 04:11:07 PM »

You have a voltage balun.   This should work for you:  http://www.balundesigns.com/model-4113-4-1-current-balun-1-5-54-mhz-3kw/

Yes, keep the ground wire outside, and bond it to the feed, outside the wall.   Ground rod and house ground rod.   
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