Antenna/Amp Speaker Noise

[W0RS]

Here is a question for the group that I cannot seem to figure out. I have a amplified speaker connected to the line out jack on my police scanner (bluetail technologies). I do have alternator noise but here is my issue...

The car is shut off, scanner power pulled from cigarette lighter plug. I have noise still coming from speaker although not alternator whine, it's just noise. When I disconnect the antenna from the scanner all is quiet, if I reconnect the antenna, noise reappears.

Anyone have suggestions as to the cause and a cure? 🤔

 

[prcguy]

Probably a ground loop between the car battery negative attachment and the point where the antenna grounds. In this case current can flow on the coax shield and audio cable shield trying to equalize the grounds and that induces noise into your amplified speaker. When the car is running and the alternator is charging you are getting rectified but not filtered DC current on the audio shield and that makes a whining sound.

The fix would be an audio isolator or transformer in the audio line between the scanner and amplified speaker.

Here is a question for the group that I cannot seem to figure out. I have a amplified speaker connected to the line out jack on my police scanner (bluetail technologies). I do have alternator noise but here is my issue...

The car is shut off, scanner power pulled from cigarette lighter plug. I have noise still coming from speaker although not alternator whine, it's just noise. When I disconnect the antenna from the scanner all is quiet, if I reconnect the antenna, noise reappears.

Anyone have suggestions as to the cause and a cure? 🤔

 

[W5lz]

From your description it seems that there is some kind of RF generator running all the time in your vehicle. The only thing I can think of is maybe the vehicle's computer, or whatever is constantly connected that uses some sort of voltage converter?

 

[vagrant]

I use this $11 isolator and it solves my noise problem. In fact I just purchased another as a spare for testing.

 

[W5lz]

Okay. So what exactly does that 'isolateor' consist of?

 

[doctordialtone]

Okay. So what exactly does that 'isolateor' consist of?

I use one too.

It's a 1-to-1 transformer.

 

[kruser]

I use one too.

It's a 1-to-1 transformer.

Yep, and they have been around for a many years. I used them back in the 70's for audio patching problems caused by ground loops. I often had to build my own though.

You can also use two cheap 300 to 75 ohm baluns used for TV antennas hooked back to back if you are getting ground hum coming in from a cable tv connection if you don't have the proper isolator to do the trick. These baluns are not for the typical audio ground loops discussed in this thread though but they operate on the same principal using the transformer in the balun.

 

[doctordialtone]

I often had to build my own though.

Yep. I built my own using a multi-tap transformer from a 70 Volt paging speaker.

Works great!

 

[prcguy]

It breaks the audio ground lead, some use a capacitor and some use a 1:1 transformer. It breaks up ground loops and eliminates equalizing currents on the audio shield which gets induced into the audio center conductor.

Okay. So what exactly does that 'isolateor' consist of?

 

[cmdrwill]

Best bet is the audio isolator that has a transformer in it.