[Oldgeezer]

Need help with an RF noise issue between my Advanced 3500EE EFIS and a Garmin SL40 radio. I have the instrument panel and electrical wiring installed and everything seems to working ok, but here is my problem.
With the EFIS on and when keying the mike and transmitting on the SL40, the amp meter on the EFIS will drive up to red line until I release the transmit switch, then goes back to zero. I am using RG400 coax cable and have moved it away from other wiring. Also metered the cable between pins to check continuity and any shorts, looks ok. The Comant whip antenna is mounted under the pilots legs just forward of the main spar and I removed the gasket between it and the belly skin for a good ground plane. The straight line distance between radio and antenna is about 2 1/2 feet. Spoke to both manufactures and they believe I am getting RF noise into the EFIS sensor wiring. The wings are not mounted yet.
Two suggestions were made and looking for any solutions others might have.
1. move the antenna back further under the baggage compartment.
2. remove the single stranded wire from the EFIS harness to the shunt and replace it with a shielded wire.
Would like to solve this problem before riveting on the forward skin over the instrument panel. Any help would be appreciated.
Thanks
Oldgeezer

 

[tim2542]

Some thoughts...

First, is the radio working correctly, good Rx and Tx reports? Find a local Ham and borrow his dummy load. This will contain the RF emitted from the antenna and will tell you something if it changes the reported high current warning.
Second, what is the alarm set at? It may be set too low, and the transmitter will be using 5~8 amps so this could be the problem.
Third, how and where are you sensing current? I can't speak to AFS equipment, but I'd make sure what it is reporting is accurate. These Hall effect sensors sometimes are finicky wrt to placement & configuration settings. So find yourself another ammeter, preferably a clamp-on inductive type like a Fluke or similar and see if its reporting correct information.
If its reporting correctly and the alarm is not set too low and the dummy load makes no difference, then I need to scratch my head a while, but you might ask yourself why do I need an ammeter anyway if I have a voltmeter?
Good Luck!
Tim