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Com transmit blanking out VOR CDI

 
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donjohnston



Joined: 13 Dec 2009
Posts: 210

PostPosted: Mon Nov 07, 2016 6:14 am    Post subject: Com transmit blanking out VOR CDI Reply with quote

I've been chasing an issue where whenever I transmit on either com radio, I lose the CDI needle. This only happens on VOR's, not localizers.

Specifics:

Composite aircraft with foil com antennas in the vertical surfaces and foil nav antennas in the bottom of the main wings. The antennas are based on Jim Weir's antenna designs (RST Engineering). The com and nav radio's are Val Avionics 2KR models. Absolutely no known problems with com transmission or reception. Never had any complaints from ATC about weak transmissions.

Localizer performance is fine. Rock solid needles, transmitting on the com radio has no effect on the localizer. With VOR's, the needle doesn't seem to be as steady. A little... wobbly. Tried numerous VOR's and transmitting always knocks out the needle.

Instrumentation is Grand Rapids HXr EFIS. The CDI is represented in the EFIS. There is no separate, standalone, traditional CDI.

This occurs whether I transmit on Com 1 or Com 2. I only have a single Nav radio and I have tried this with both nav antennas.

Val Avionics initially said it was the com antenna "blanking" out the VOR signal. But after hearing that I had no problems with the com performance, they said it was the nav antenna. Rolling Eyes

I swapped email with Jim Weir and he basically said it's not the antennas.

Local avionics shop isn't sure how to proceed other than to suggest trying a traditional antenna.

Wondering if anyone else has run into this and what the solution was.


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Airdog77



Joined: 24 Nov 2013
Posts: 80
Location: Northern Virginia

PostPosted: Tue Dec 18, 2018 4:27 pm    Post subject: Re: Com transmit blanking out VOR CDI Reply with quote

Don,

Just ran across this post and am wondering if you ever resolved your issue?

I'm 'close' to finishing up a Long-EZ and have a Garmin GPS unit for COM1 and NAV1, but was considering the VAL 2KR for COM2 controlled via a GRT HXr.

I of course have the Jim Weir foil com and nav antennas as well, so again am very curious if you were able to resolve your VOR interference issue?

Cheers,
Wade


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Airdog
Wade Parton
Building Long-EZ N916WP
www.longezpush.com
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