EFIS interfering with my 496

[Chino Tom]

When helping a friend install his AFS 4500 a few months ago, i could not
get his 396 to hold satellite reception when the 4500 was powered up.
Remembering a post by Vic S with the same issue, see here:

http://www.vansairforce.com/communit...hlight=antenna

We then moved the GPS antenna from the glare shield to the center bar
and the 396 worked as advertised. Knowing this issue, when I upgraded my 3500 to a 4500 this week, I moved my glareshield GPS and XM antennas from my 496 to under the cowling. Much to my dismay, the GPS would not maintain reception (XM is fine) with the EFIS powered up. So I moved the GPS antenna to the rear of my -8A. Now it worked great. Having not tried the GPS antenna on the glareshield at all, I was suprised to find on a test flight, that moving the puck back to the glare shield had no determental effect on reception. So now, i coiled the antenna wire behind the panel and moved the antenna puck back to the glareshield. Guess what.... no reception again. Seeing a pattern here, I moved the coiled antenna wire from behind the panel to the glare shield and low and behold satellite reception returned to normal. Because the GPS antenna is long, I had coiled the excess behind the panel when the GPS antenna was under the the cowling (the XM lead is much shorter and did not need to be coiled). I suspect the unshielded 496 GPS antenna lead while coiled and close to the EFIS was the problem all along, not having the puck on the glare shield.

PS... I love the SV in the AFS Advanced Deck 4500!

[tcone1]

I had the same experience with a friend's RV-10. His was a AFS-2500 that started leaking RF. It worked fine for a few years with his 396, then all of a sudden the 396 wouldn't find enough satelites to navigate. We got lucky while trying to diagnose the problem and noticed that the antenna placement affected the signal strength on the info page. We isolated the problem by shutting down one system at a time until we found that all interference vanished when the 2500 was switched off.

My friend sent the 2500 back to AFS and was told that there was nothing wrong with the unit. We re-installed it and the problem persists. We tried the factory's recommended shielding and chokes...funny that the factory recommended shielding and chokes when they claim no interference could be coming from the 2500???

The only solution was moving the gps antenna away from the 2500.

[Tom Martin]

This is a most interesting thread! I upgraded to the 4500 this winter, fantastic, and all season I have been having problems with my up to now totally reliable 496. It can take up to 15 or 20 minutes to capture satellites. I had done all the upgrades to software with no improvement. The last time I had it out of the plane I fired it up with the portable antennae and it worked great and so I thought the problem was solved. Installed back in the airplane and no go. My 496 is wired to come on with the master switch. I found that if I powered the 496 up, with it's internal battery, before applying aircraft power all was well. Once it grabbed the satellites applying external power did not seem to affect reception. My 496 antennae is on the glare shield and all the extra cord is coiled up beside the 4500. Thanks for the information, I would not have considered an interference issue but it certainly sounds like a possibility.