Hummmmm during transmissions

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Bentley

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Premium Subscriber
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Feb 5, 2006
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653
Location
Freehold, NJ (Monmouth County)
Hi guys, been scanning for over 20 years but new to the broadcasting end of it so please bear with me.

I'm getting a pretty bad hum during transmissions on my feed. I've searched the forums and tried / ruled out pretty much everything I can think of.

First thing I thought was the wall wort, I would have purchased a ground loop isolator but I unplugged it and ran of batteries and the hum is still there.
I have tried two different scanners, both with same results. I'm using all mono cables, actually the exact ones described here.

All plugs and cables are pushed all the way in / clean.

I did some testing and when I put on a weather channel the hum is gone, but when I go back to the primary channel, the hum is back.

I want to have a headphone splitter so I can set up a speaker to run off the same scanner that is providing my feed. I get no hum out of that speaker. I disconnected the splitter and tried running the cable directly from scanner to PC and the hum is still there regardless if I have the splitter in place or not.

I am using the line input (not mic) of the PC. I tried playing with the volume settings on there IE: scanner volume high, line in volume low and vice versa. The only thing I could not find a setting for was the gain on the PC line in??

I've heard much worse feeds than mine, but I've also heard much much much better. I would really like to improve the sound quality, so any help would be great.

Should I try an external (USB) sound card?

Here is a link to my feed in case you want to hear it for yourself.

Freehold Township Police
 

glennpd

Member
Joined
Sep 14, 2004
Messages
1
Hum in audio

I ran two Radio Shack PRO-92's, a Pro-96, and a PC controlled PRO-2006 running off a 2 different power cubes for the required 9 and 12 volts DC. Needless to say, between the two power cubes and the PC, I was also plagued by 60 Hz hum in all the audio streams. I bought several Radio Shack Ground Loop Isolators (current Radio Shack Model is 270-054) and moved them around at different points in the audio cables until the problem went away. I never did discover exactly how/where the problem originated.

Also, on most modern Windows operating systems, there is a sound icon in the control panel (view all control panel items) that allows you to set the audio source and input levels (microphone or line-in) and to select the audio output device and mix levels. It largely depends on your sound card and the audio drivers (dll's) installed by either Windows (default) or the sound chip manufacturer.
 

jim202

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Joined
Mar 7, 2002
Messages
2,668
Location
New Orleans region
Hum can be from a number of reasons. Trying to locate the source can be a test of your skills and how much time you want to spend looking for it.

I would start with asking how high the gain is set on the computer to get your audio to sound reasonable? If the gain is way up, then you need to start looking why. It could be an issue with a DC bias coming from the radio your using for the audio source. Try taking a volt meter with your connections off of the radio. See if there is any voltages from either side of the source your using. If your taking the source right off of the speaker connections, that is a bad move. You might have to insert a series capacitor of say 1.0 uf to block the DC voltage.

If your using the speaker connections, it might be better to use an isolation transformer. Cap couple the speaker side on one wire between the radio and the transformer. This will prevent the transformer from causing a problem. On the other side of the transformer, you should have a high impedance to try to match the audio into the computer.

If your coming off of a headphone connection, you might still have the same issue with a DC bias voltage. Again try coupling your audio through a 1.0 uf capacitor between the radio and the computer. The exact value is not critical. The larger the cap, the lower frequencies will be passed. If you lower the cap value, it will tend to pass more of the high frequencies. Part of the roll off or center of the frequencies that will pass better might also depend on how the radio audio circuitry is set up.

Let the group know what you find out.
 

webstar22

policescanner.ca
Feed Provider
Joined
Dec 21, 2003
Messages
863
Location
Ontario, Canada
Before you all crazy just order one of these NEW Mini USB 2 0 3D Virtual 12Mbps External 7 1 Channel Audio Sound Card Adapter | eBay

This is what I use for my feed without issues. Rule out the sound card on the computer.

Also as for the splitter, stream your feed form the REC Out and then you can use the Ext SPeaker for your own use. Nice thing about RECOUT is you can change the volume on the scanner all you want without killing the audio on your feed.
 
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