GMRS Interference from rear brake/turn lights [SOLVED]

[GotMojo]

Here's some traces of the brake lights. You can clearly see the PWM riding on the DC line -- which is pretty dirty to begin with. Truck is ON but engine is not running.

It appears that the turn signal noise has 2 components. The first is the on/off voltage spike, the second this same PWM.

No brake

Brake applied

I think a simple line filter will resolve this. I'm going to order this one and hope for the best. It comes with t-connectors so it's a simple plug'n'pray.

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[Tbone289]

I think a simple line filter will resolve this. I'm going to order this one and hope for the best. It comes with t-connectors so it's a simple plug'n'pray.

Thanks for that. The PWM is >30kHz then? No wonder I can't see it...

 

[GotMojo]

On a hunch, I plugged in a different radio -- Wouxun XS20G and it does not suffer the same interference. Same power source, same antenna. I think I can conclude that whoever makes this radio for Midland cheaped out on the input filtering or just didn't bother to put in any at all.

I'm surprised I haven't seen more complaints about this. It's kind of an important thing for a radio...

 

[GotMojo]

Thanks for that. The PWM is >30kHz then? No wonder I can't see it...

It looks to be less than that but it's definitely in the kilohertz range. Sorry about my crappy traces. I was only looking to validate that it was PWM and that the signal was present on the DC input.

 

[GotMojo]

Received the filter today and plugged it in. It greatly reduced the noise but didn't completely kill it.

Bummer.

It's close enough to background noise that I'm just going to live with it. The fact that it's only present when braking or blinking makes it a bit more tolerable as well.

The only real solution is to completely isolate the power from the car or get a different radio. Neither of which I'm willing to do right now.

Can't recommend this radio (Midland 275) because of this 'feature', especially at the price vs cheaper offerings that have adequate power filtration.

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