Author Topic: Audio cable to eliminate noise  (Read 11015 times)

Offline MSN ATC

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Audio cable to eliminate noise
« on: December 22, 2004, 11:44:54 AM »
I am testing a new computer and scanner for my stream but am getting a lot of noise (background hum). I assume its from an impedence mismatch between the scanner and audio card. Is there an off-the-shelf cable to eliminate this noise?


Madison, Wisconsin ATC

Offline JoelAVguy

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Does it cycle?
« Reply #1 on: December 22, 2004, 11:59:11 AM »
There are many things that I could be.  Make sure the AC plug in which your computer, scanner etc.... has a good ground.  You can test this with a voltmeter.
Is the hum steady of does it cycle?

Offline dave

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Re: Audio cable to eliminate noise
« Reply #2 on: December 22, 2004, 12:01:53 PM »
Quote from: pweeden
I am testing a new computer and scanner for my stream but am getting a lot of noise (background hum). I assume its from an impedence mismatch between the scanner and audio card. Is there an off-the-shelf cable to eliminate this noise?


This is a ground loop.  

The ground potential of the scanner may be higher or lower than that of the computer and the computer's ground path to earth ground, or ground impedance, may be higher or lower than that of the scanner.  The result of a ground loop is audible 60Hz hum.

These unbalanced components share a common ground bond between them via the shields of their interconnect cables, or via the ground wire of their AC power cords.

The ground bond via the AC power cords can be problematic because the cords may be different gauges, have different contact mechanical integrity at the outlet, and have different distances to travel back to earth ground.  All these variables can create differences in the ground impedance of each component and opens the door for ground loops and system noise.

Check this web site out...you may find some good suggestions here and you will learn something:

http://www.epanorama.net/documents/groundloop/index.html

I usually find that the safest and most convenient approach is to connect the scanner's ground (via the BNC plug or via a screw to chassis ground) to the PC case (usually via a screw on the back of the PC case).  Other methods get more complex and sometimes don't work...plus they can pose safety hazards.

Dave

Offline JoelAVguy

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Right on
« Reply #3 on: December 22, 2004, 12:23:33 PM »
Dave is right on; let us know what happens with the BNC idea.  Remember SAFETY FIRST when it comes to electrical wiring!

Offline MSN ATC

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Audio cable to eliminate noise
« Reply #4 on: December 22, 2004, 12:41:04 PM »
Thanks for the help, guys.  I have the stream running, such as it is, and you can hear the hum.  Go here:
http://www.weedengraphics.com/msnatc.html

I will be mounting a new antenna tonight. Look for improvements in the next few days.
Madison, Wisconsin ATC

Offline JoelAVguy

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Hard Drive
« Reply #5 on: December 22, 2004, 12:54:21 PM »
Where is the Scanner in relationship to the computer?

Offline MSN ATC

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Audio cable to eliminate noise
« Reply #6 on: December 22, 2004, 01:18:05 PM »
The scanner sits right on top of the computer, an old ThinkPad with the lid closed. Its at a friend's house and I wanted to take up as little space as possible. Both are pluggedinto the same power strip.
Madison, Wisconsin ATC

Offline JoelAVguy

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Hard Drive
« Reply #7 on: December 22, 2004, 01:39:25 PM »
I listed to the feed for about 20 min….  The ground loop is your best lead…. however it could be interference from the hard drive.  Dave what do you think…?

Offline MSN ATC

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Audio cable to eliminate noise
« Reply #8 on: December 22, 2004, 02:00:35 PM »
You will hear very little if you listen right now.  I had this running at a friends house about 1/2 mile from the tower up until a month ago. Ran great for two years. Scanner died, then the computer died (they were both eBay relics). I now have a new (used) scanner and laptop but in a new location about five miles further away and with no external antenna. We hope to mount the antenna tonight, although it will be below zero here. I found this site doing a goole search for live stream noise.
Madison, Wisconsin ATC

Offline dave

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Re: Hard Drive
« Reply #9 on: December 22, 2004, 02:26:26 PM »
Quote from: JoelAVguy
I listed to the feed for about 20 min….  The ground loop is your best lead…. however it could be interference from the hard drive.  Dave what do you think…?


Ground loop.