COM interference with ADAHRS

[Sportsman7064]

While building my Glastar Sportsman in my basement, I noticed a few issues with the Skyview when I finally got the panel done. Each time I key the mic, the temps on the EMS page would jump. Also, the PFD would show sudden jumps in altitude (and VSI). All of these got worse when transmitting near the end of the aviation band (in the 130's).

I sent my EMS module off to Dynon and they made some internal changes and the EMS issues have nearly completely disappeared. However, the PFD still shows wild fluctuations when I transmit. I waited until I had the plane at the airport where I could be away from buildings, but the issue persists.

Is there a similar hardware fix for this condition? I have the ADAHRS unit in the only place I can put it, pretty much - behind the rear seat mid-way between the steel cage and the aluminum tail. I also have the factory dipole antenna in the vertical fiberglass tail, and my COM2 antenna is a Bob Archer unit bonded to the side of the fuselage about 3 feet from the ADAHRS unit.

I was really hoping to keep all the antenna inside the plane and keep her aerodynamically clean (as much as I could).

Any thoughts?

Thanks,

Russ

 

[dynonsupport]

Russ,
I have a Sportsman too, so I have some thoughts

First, the AHRS near the aluminum in the tail is no issue. Only steel (magnetic) is an issue. In our case, we have the AHRS mounted to the roof, about 2' behind the baggage bulkhead. It works great there.

We have one com antenna in the tail, as is standard, and another bonded to the side of the fuse, right next to the AHRS. Probably less than 1' away. No problems.

So, it's more complex than just distance. We've only seen this issue once or twice before, and it's actually the RF energy getting into the wires going to the AHRS, not the energy at the AHRS itself.

So first, do both COM1 and COM2 do it, or only one?

What kind of coax did you use to run to the antennas?

Can you flop COM1 and COM2 antennas between the radios and see if it follows the radio or the antenna?

We do have a filter that you might be able to plug in at the AHRS to fix this. Let us know the above answers and we'll have a better sense if it will work.

Congrats on getting the bird flying!

 

[Sportsman7064]

The ADAHRS unit is on a shelf just behind bulkhead A. My antenna set-up sounds the same as yours. The Bob Archer antenna looks like a large E made from thin aluminum sheet stock. The antenna wire for the copper dipole unit was from the factory but it is a tri-axial cable (Not RG-400). My COM2 is wired wth RG-400 (as are all the others - a VOR antenna in the right wingtip, and the transponder antenna also in the tail, located on the other side and a bit further back from the COM2 antenna.

The condition exists with both COM units. None of the network cables are shielded wiring, but is there something I can do to help prevent the RF energy from entering the wires?

 

[jakej]

DS may have a better solution however a simple (read inexpensive) test would be to fit a clamp on ferrite at the Com antenna end, available from RadioShack or other electronics supplier.

Jake J

 

[Sportsman7064]

Will a clamp on ferrite be more effective than the Dynon filter?

Thanks

 

[jakej]

Will a clamp on ferrite be more effective than the Dynon filter?

Thanks

Maybe/ maybe not but it's simple & cheaper

Jake J