Nav Interference

[Mverkade]

Hey all,

First post here. I would appreciate some input/direction. I fly an old Skyhawk and am doing some IFR work in it. Old school KX170’s and King CDI’s, not sure on the exact models but Nav 1 has Loc/Gs and Nav 2 is VOR/Loc. Just had a GMA audio panel installed and a few other things changed. Prior to the avionics work we had an issue with interference on Nav 1 whenever transmitting over either com, the glide slope needle deflects when using PTT. I had hoped that this would have been cleared up with an actual audio panel and wiring clean up. I’m still getting the issue. Any words of wisdom that I can start looking for prior to spending some more $$ and getting it back to the shop? ILS, LOC and VOR track great. It’s just when transmitting that I have an issue.

 

[bluerooster]

I would first suspect the coax. The KX170 does not have a glideslope receiver. The GS receiver is integrated in the Indicator. There may be some faulty coax allowing "cross talk" between the two. Somewhere in the antenna system there should be a diplexer which splits the signal from a single nav antenna usually mounted high on the tail, into VOR/LOC and GS. could be as simple as a bad connection at that point. I try to keep the run from the diplexer to the receivers as short as I can, with one long run to the antenna.

 

[Mverkade]

Thank you for the advice. I’ll check those connections. We have an annual coming up shortly which should give me some easier access to look for discrepancies.