A Brain Teaser

John G · Post by **John G** » Wed Feb 04, 2004 6:00 am

This isn't Motorola related but I thought someone might have encountered this. Did a ham radio install in a new Ford diesel pickup. Power leads go straight to the battery. Antenna was mounted in the gap between hood and fender with a trunk lip mount. If the motor is running, radio transmitts a noise similar to ignition noise. Of course it isn't since this is a diesel. Transmit into a load, no noise. Transmit into a mag mount on roof, no noise. Put a maf mount on hood, still get noise. Ran the radio off an ac power supply, still get noise. He is going to add a ground plane to a fiberglass bed cover and put the antenna there. Can't do a roof mount because the antenna would scrape his garage door. Anyone seen anything like this?

jim · Post by **jim** » Wed Feb 04, 2004 6:40 am

Could you describe this noise?

If this is a Powerjoke, I'm thinking that you may be getting noise from the Diesel injection system's 140 VAC switching power supply. This unit is what drives the injectors on the Powerjoke engine. This is usually located on the driver side inner fender at the rear of the fender. This is one noisy SOB that makes an "ignition sound." Move the antenna and power leads from this area. Add a redundant power lead ground at the radio. Install the power leads to the battery in a "twisted pair" configuration.

You might also want to try to run a braided cable from the 140 volt unit to the engine block, but you still have a very dirty signal coming from the harness on this thing.

Aces-Warehouse · Post by **Aces-Warehouse** » Wed Feb 04, 2004 11:26 am

Supply a power ground loop isolater on the power source and test it then.

John G · Post by **John G** » Wed Feb 04, 2004 12:23 pm

We ran the radio from a 120 volt AC supply so the radio wasn't in any way connected to the vehicle power supply and still had the noise. We did conclude that the noise was fuel injectors but couldn't figure out how it was getting into the radio. We even went with a mag mount antenna so there would be no electrical connection to the vehicle. Still got the noise as long as the antenna was in proximity of the hood.

007 · Post by **007** » Wed Feb 04, 2004 10:29 pm

The noice is getting induced by the injector power supply thru the air...no physical connection is needed. It is throwing RFI all over under the hood, and the radio is "hearing" it thru the coax mst likely. Could be the particular mount and coax length, so play with location and length...