Hum (ground loop?) in feed

bwstein · #1 (**permalink**) 10-13-2009, 05:00 PM

Hello all,

I've got a couple of feeds that I'm providing. One is using a base station scanner and the quality seems to be pretty good. One is provided using a handheld with a DC power supply attached. That feed has a hum that is only present when the power supply is connected. I've tried running a ground wire between the PC and the radio as well as swapping power supplies and trying a few different radios with no luck. I have to assume others have a similar setup and have worked around this issue. Am I missing something?

Thanks
Ben

04Z1V6 · #2 (**permalink**) 10-13-2009, 06:11 PM

You said it I solved mine with a ground loop isolator and my notebook power supply gave me allot of noise, I got this solved with a very good surge arrester outlet that also cuts out RF noises.

richtidd · #3 (**permalink**) 10-13-2009, 06:33 PM

Quote:

Originally Posted by bwstein

Hello all,

I've got a couple of feeds that I'm providing. One is using a base station scanner and the quality seems to be pretty good. One is provided using a handheld with a DC power supply attached. That feed has a hum that is only present when the power supply is connected. I've tried running a ground wire between the PC and the radio as well as swapping power supplies and trying a few different radios with no luck. I have to assume others have a similar setup and have worked around this issue. Am I missing something?

Thanks
Ben

You may need to install as audio isolator between the radio and computer.

You can get one from Radio Shack: RadioShack.com

IowaBrian · #4 (**permalink**) 10-14-2009, 11:29 AM

To get rid of the ground loop one of the isolators is a good way to go for our application. Back in the old days of installing high end car audio and also fixing bad installs we would see group loop issues all the time and they always tried one of these $20.00 fixes they do work to a point for what we want I think it will work good enough but for high end audio we chucked them in the trash and found the source of the bad ground and fixed it that way.
To do that at home would cost more than it is worth if you are only using a scanner. I have the same issues but my house is 60 years old and a Tim Taylor School of wiring before I moved in so to say I have bad grounds or no grounds is understatement.

N_Jay · #5 (**permalink**) 10-14-2009, 11:35 AM

Are you sure it is a ground loop and not power supply hum?

You can spend a lifetime fixing the wrong problem.

bwstein · #6 (**permalink**) 10-14-2009, 12:56 PM

Quote:

Originally Posted by N_Jay

Are you sure it is a ground loop and not power supply hum?

You can spend a lifetime fixing the wrong problem.

No, not at all sure. In fact I suspect it may be more of a power supply hum than ground loop. The location it's going to is assuredly properly grounded and I verified that with an outlet tester that shows good ground. I've tried multiple power supplies and while I get a hum with all of them it varries from PS to PS. Is there a trick to removing the hum from the PS? Do I need to buy a better PS? One of the interesting things that I noticed is that if I'm not using the headphone out on the scanner but rather just using the speaker on the scanner itself I don't have the problem. Don't know if this points back towards a ground loop or not.

Thanks
Ben

N_Jay · #7 (**permalink**) 10-14-2009, 01:36 PM

An outlet tester is near worthless for finding ground loop problems.
A test for a true ground loop problem is to run the radio on battery, but tie the ground to the outlet ground that you suspect to be causing the problem.

A test for a power supply hum problem is to disconnect from the computer and put a battery powered amplifier on the radio speaker connection and listening for hum.

In general "better" power supplies should have less hum, but unfortunately more expensive does not equal "better".

mcscanner · #8 (**permalink**) 10-14-2009, 01:41 PM

Two things you could try that are easy.

Make sure the power supply is plugged into the same outlet as the computer. If the power supply has a non-polarized plug flip it over and see what happens.

Outlet tester is a good check to ensure a ground of some sort is present and the outlet is wired correctly. If using different outlets then the ground wire back to the breaker box could be on different legs.

I have known moving all devices to the same outlet to improve the hum issue. I can’t say that I have ever known flipping the plugs over to work, but you never know.

Tim-Elyria · #9 (**permalink**) 10-14-2009, 05:17 PM

I have use a 1to1 audio transformer wired inline with the audio cable going from the scanner to the computer. they are only a few bucks at radio shack. Catalog #: 273-1380 . This isolates any actual contact from the scanner to the PC but still sends the audio through.

N_Jay · #10 (**permalink**) 10-15-2009, 12:19 AM

Unless the ground loop is on the antenna line.

feedus · #11 (**permalink**) 10-15-2009, 05:10 PM

I too have had a problem with a hum. I use BC785, and have narrowed it down to 2 poss causes. I placed the radio shack isolator on the feed but I still have the problem. I switched transformers and still had the problem.
I found that my antenna wire wasnt properly soldered so I re-did that (yes both ends) still I have the hum in my feed. I switched it over to 2 other computers (thinking it may be the computer problem) still had it.
So its some where inside my BC785D. The hum can only be heard if the listener has there volume on the sound card turned all the up.
So since I cant find the source inside the 785 I have chose to leave it alone (for now) unless someone here has any other ideas I can try.
Yes the ground on the antenna did reduce alot of the noise.