P

pestar

I'm New Here
I have a frustrating problem that is bugging the heck out of me. I have dual MGL Voyager G2's and 1 x MGL Xtreme.

At random intervals I will loose my GPS signal to each EFIS, not simultaneously but all get affected. The New Zealand agent is assisting me but we have not solved it yet. I have relocated the GPS antennae away from each other. We have shortened the GPS coax cable to eliminate induced interference and correctly re-terminated the coax, there are no loops or crossovers in each of the 3 GPS cables.

We suspect it is interference but where? Have installed a ferrite bead on each of the GPS's coax . All cabling where low level signals are carried are all shielded (one end only).

Any ideas of where to look and what instrumentation to use to track this down. I have a laptop scope in house.

Plane is wired on Bob Knuckells principles (Aero Electric Connection) and apart from the fact that I have a lot it is still pretty standard.

There is nothing consistent when the GPS's become available or not available, some-days it has been perfect others like today they all just came and went at random intervals.

This is a real propeller head problem, I would certainly appreciate any thoughts from other electron jockeys.

Cheers Peter

Peter Armstrong
Auckland, New Zealand
 
Can you fly with just one GPS turned on and active? If so, start with one and only one powered on, fly for awhile and see if the problem returns. This may help isolate the problem.
 
Any chance all of your GPS antennas are co-located?

There are a number of posts on VAF describing signal reception issues and drops when the multiple GPS antennas are located close together.

If you can test one GPS at a time, it may help to actually move or remove the other GPS antennas.
 
I'm shooting blind here, but be aware that some GPSs can be affected by certain specific frequency settings on the com radios, whether transmitting or not. It took me a while to figure that out after repeatedly losing my (G296) GPS signal when flying in certain areas and thus using certain frequencies.

Also, try repositioning your ELT antenna, even though this sounds weird. Someone told me that ELTs have a passive filter arrangement that can actually be excited in certain situations such that it itself can generate RF harmonics that can interfere with GPS reception. Sounds like a little voodoo to me and maybe I'm not explaining it properly, but the guy was very avionics knowledgeable. This wasn't the problem in my case, but it might be worth a check.
 
Thanks for the replies.

Have a plan of attack in place after further testing. Going to put an adhesive based aluminum under the cockpit coaming to shield the GPS' from any RF from the instruments.

We have a suspicion that their maybe 1 faulty antennae that is causing the problem so I have a spare and will swop each one individually and see if the results change.

Interestingly this problem is now also affecting my SpiderTracks device which is a completely standalone GPS unit and only has power going to it. This proves to me that I am getting extraneous RF from somewhere.

Thanks Peter


Peter Armstrong
Auckland, New Zealand
 
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