Hum in audio with antenna

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frazpo

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I have an RS discone mounted to a metal pole. The metal pole is in the ground a couple of inches and it is attached to the house about 3/4 up. The problem is a hum in the audio no matter what scanner I connect it to. There is nothing inline between the scanner and the antenna. Remedies? Thanks.
 

frazpo

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OK. I have a cheaper version hanging in the attic with no ground and I don't have this problem. This antenna didn't use to have the hum that it has now. Very weird. I'll see if I can get it grounded better.
 
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How are you powering your scanner, sounds like a ground loop associated with your power source, do you have an external audio connection to a computer or other device?
 

jim202

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The indications from the details you have given is that the scanner is causing the hum due to it being grounded by the coax which in turn is grounded by the mast. This is probably all caused by what ever power supply your using to power the scanners. My bet is that it isn't grounded and your experiencing a ground loop issue from the power supply.

My suggestion would be to find a good ground to make sure the negative of the power supply is tied to ground. By any chance does the power supply have only a 2 conductor power cord? If your power supply does have a 3 wire power cord, then you need to look further.

I would start with making sure the power outlet your plugged into has a good ground connection. You can test this real fast by looking at the outlet with a volt meter. You will notice that the outlet should have a long slot and a short slot. The short slot is the hot leg and the long slot is the neutral.

If you take a volt meter from the round pin (ground) to the short slot, you should see 120 volts AC.

If you take the volt meter from the long slot to the round pin, you should see nothing.

Now put the meter in the Ohms position, and short the test leads together. You should see 0 Ohms. Take the test leads and go from the round ground pin to the long neutral slot. You should see close to zero Ohms again. If not, your missing the ground connection at that outlet.

If in your testing of the outlet in the first few steps, you don't get the 120 volts and no volts in the locations I told you to measure them in, stop. The outlet is wired wrong. Trying to use an Ohm meter on a circuit that has voltage on it will damage or blow the meter up.
 

LtDoc

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I think it would be safe in saying that the antenna isn't the source of that hum. It could be coming from a number of other places, and I think I would start looking for those other 'places'. They can run from the power source of the receiver, something electrical near that receiver/feed line/antenna, to the color of socks you're wearing. (change your socks first, that's the easiest one to do)
- 'Doc
 

frazpo

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Thanks all for the feed back. I will check what is mentioned.

I do not have any power supplies but the grounded source is a possibility.

Thanks again


Sent from my iPod touch using Tapatalk
 

frazpo

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OK. It seems to be coming from the feed computer. During my initial test I was basing my audio from the computer speakers (sound card for feed). The hum is not present until I plug the mono plug in the scanner. However, it still only does it on one antenna. So will the isolator fix the issue if it is coming from the computer? I probably have some computer power supplies around here. I wonder if I should swap and see if that would help.
 

ak4fn

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OK. It seems to be coming from the feed computer. During my initial test I was basing my audio from the computer speakers (sound card for feed). The hum is not present until I plug the mono plug in the scanner. However, it still only does it on one antenna. So will the isolator fix the issue if it is coming from the computer? I probably have some computer power supplies around here. I wonder if I should swap and see if that would help.
You need a ground loop Isolator. From "Setting up your Broadcasting Station" Wiki Page:
"The use of an audio isolator can help to eliminate hum between radio and computer due to different a.c. power grounds. Radio Shack has an isolator listed in #Related Links. It is an audio transformer that blocks d.c. continuity between the scanner housing and the computer case."

They Mention Radio shack but here is a list from Monoprice for the Ground Loop Isolator and and cables, for just under 9.00 plus shipping.
4 Channel Ground Loop Isolator | Isolator
6ft 3.5mm Stereo Plug/2 RCA Plug Cable - Black | 3.5mm & RCA Audio Cables Ground Loop Isolator to computer or scanner
6inch 3.5mm Stereo Plug/2 RCA Jack Cable - Black | 3.5mm & RCA Audio Cables other side of Ground Loop Isolator
 

frazpo

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Thanks for the info. Not sure how I have gotten along this long without any noise issues. I have read the posts and wondered how it was fixed but really never needed it. It just seem to have started recently. That's why it makes me wonder about the computer power supply or another part. Thanks for the parts list. It is appreciated.
Thanks alot.
 

ak4fn

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Thanks for the info. Not sure how I have gotten along this long without any noise issues. I have read the posts and wondered how it was fixed but really never needed it. It just seem to have started recently. That's why it makes me wonder about the computer power supply or another part. Thanks for the parts list. It is appreciated.
Thanks alot.
You can try to make sure that the computer and the scanner are on the same power strip, that may make the difference.
 
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