CDM Interference From A Rotating Lightbar

[davee]

When the lightbar is turned on the UHF CDM quits receiving in trunk mode only. Lightbar has 4 rotators and any one causes interference. Tried caps across the motors but din't help. A line filter at the radio didn't help either. Anyone with any suggestions?

Dave

[thebigphish]

is moving the antenna a possibility? perhaps an alternative mount?

[Hightower]

First, try relocating the power wires for the radio, and move the antenna coax to a different location in the vehicle.

Now this one even surprised me at ridding radios of motor noise from fans, and the like. Take the power wires from the light bar, seperate the hot and neg. wires. Now you have 2 wires (hot and neg), wrap or braid these wires around each other.You don't need a real tight braid , but a loose brade does the trick.

Had a fan that I put caps on, capped the radio with different values too. Nothing got rid of the fan noise till someone recommended I wrap the power wires around each other. I was like, ya right!!! Last resort, i wraped the wires around each other, and the noise was GONE - no caps or chokes what-so-ever. I was shocked at how well it worked. Give it a try

[fineshot1]

Now this one even surprised me at ridding radios of motor noise from fans, and the like. Take the power wires from the light bar, seperate the hot and neg. wires. Now you have 2 wires (hot and neg), wrap or braid these wires around each other.You don't need a real tight braid , but a loose brade does the trick.

Had a fan that I put caps on, capped the radio with different values too. Nothing got rid of the fan noise till someone recommended I wrap the power wires around each other. I was like, ya right!!! Last resort, i wraped the wires around each other, and the noise was GONE - no caps or chokes what-so-ever. I was shocked at how well it worked. Give it a try

Yes - this is a method known as "self sheilding" and can help in certain situations. Its commonly used in marine (boating industry) wiring.

[jackhackett]

If your lightbar is rotating, you've got bigger problems than interference..

Anyway.... about wrapping the power wires, what you're basically doing is making a twisted pair. http://en.wikipedia.org/wiki/Twisted_pair

[AEC]

I've had a CDM install that had the very same problem with noise.

The cure was a new power supply for the strobes as the 'old' one was splattering wideband garbage and causing teh CDM1550 VHF to 'tick' when receiving on all channels.

It didn't matter if the flashers were set to the arrow stick, strobes or rotators; the power supply was simply noisy and no amount of filtering would eliminate it.

I took a sniffer (1/4 wave on cable) and connected it to the ant. port and walked around the vehicle.

The noise got progressively worse as I approached the power supply, but even enclosing the supply in a cabinet and vented/fanned, I couldn't get rid of the noise.

Scoping the leads proved out the problem....

The pulses emit a lot of wideband RF trash, and teh transistors were actually heard 'singing' while the supply was in operational load with all lights and accys. turned on.

I swapped it out for a new supply and retested...no more noise.