Shielded Wires

powers · Post by **powers** » Sun Dec 21, 2008 22:49

My A65 has Bendix Scentilla mags and non shielded wires. With the engine running I can't get a hand held with in 20 ft of the plane, because of back ground noise. Will I have to change out the wires with shielded or will the noise filters that can be mounted on the mags at least help or maybe fix the problem?

MikeB · Post by **MikeB** » Mon Dec 22, 2008 19:36

Powers,
In my (limited) experience, if you're going to use a radio and get any amount of decent reception , you'll have to come up with some kind of shielded plugs and wires. I originally had Eiseman mags on my A65 and radio reception was marginal at best. Had to be with a couple of miles of the airport to get ATIS, etc. When I installed the new engine I also installed new Slicks. Very quiet and reception from 20-30 miles away. Same with another Champ at our airport. I guess some have had limited success with filters and moving the antenna but didn't seem to work for me.

I have a JRC handheld radio clipped to the dash and while I have a whip antenna mounted in the left wing root, I really don't need it. The rubber ducky seems to work just about as well.

Mike Berg

james gevay · Post by **james gevay** » Tue Dec 23, 2008 07:32

Before I disassembled my Champ for restoration I didn't have any problems with unshielded mags and harness.

I was running a A75-8F with Eisemann AM-4's and a Icom A-22 with a David Clark 10-30 headset. I also had a wire whip antenna mounted on the right wing fairing. I did use shielded wires from the mags to the mag switch, but that was it.

There was always some amount of background noise but nothing that was any kind of a problem hearing or talking. I never got any complaints from the local tower and I could always hear them perfectly. I never really bothered with a range check but I know I could get ATIS at least 15 miles out. My setup worked perfect for what I wanted and the only thing I'll change is to add one of those small intercoms hard-wired and mounted out of the way and under the panel.

MikeB · Post by **MikeB** » Tue Dec 23, 2008 08:55

That's interesting Jim. We were running the same set up on the yellow Champ and it was basically unreadable unless you were almost in the traffic pattern at EAU. The antenna was (and is) mounted by the left rear window. I wonder if the shielded wires running to the mag switch is what made the difference.

Mike

powers · Post by **powers** » Tue Dec 23, 2008 10:17

It could be the different hand held radio. I think the icoms have an ANL function. I know my a23 does. I think I'll give the filters a try and experiment a little.

james gevay · Post by **james gevay** » Tue Dec 23, 2008 18:47

I'm not sure why yours is different. As I said there was always some ignition noise, but it doesn't interfere with receiving or transmitting. My antenna is one of those 45' wire whips mounted on the right wing fairing, it was grounded to that piece, but I know it didn't meet the size requirement your supposed to have for a ground plane.

The only time I would have a radio problem was when I passed near two 1400' radio/TV towers about 7 miles from the airport. Normally I would give them about a 3-4 mile berth and not have any interference problems.

I think the only real problem was when I borrowed one of those intercoms with all the jacks and wires coming out of it. Somehow the ignition noise was so loud you could not talk on the intercom until you reduced the power and then it was OK. Sorry I can't remember the brand name of it, it was the standard 3" X 5" size intercom. That was a spaghetti nightmare, I won't use one of those again. I'm planning on installing jacks in the sidewalls and hardwiring the intercom in.

powers · Post by **powers** » Fri Jan 09, 2009 21:35

Well, I installed the filters on my mags. It really reduced the background noise. I'm able to pick up local atis about 15 miles out using a rubber ducky antenna. Does anybody know how the filters work? What function do they serve? I know they filter out the electrical interference. But, how?

Post by **joea** » Fri Jan 09, 2009 21:53

Not sure how the filters work. PFM I guess.

Take the rubber ducky antenna off and put an antenna on the airplane and your reception and transmission will really improve.

Joe

big chief 48 · Post by **big chief 48** » Fri Jan 09, 2009 23:00

By matching the wavelenght of the offending source. Thats why it sometimes takes 2-3 tries to get the right filter. Similar principle with ANR headsets.

powers · Post by **powers** » Sat Jan 10, 2009 19:45

Very interesting. I thought is was voodoo! Thanks