GNS430W ILS glide slope antenna replacement for King KA-22

[Targhee]

I have a G600/GNS430W in my M20J.  The antenna wires on the King KA-22 glide slope antenna (mounted inside the windshield on the center pole) wires broke off when a maintenance shop pulled the sun shield off.  Now I can’t get an ILS glideslope.  I can’t seem to find a used King KA-22 anywhere.  Is there another approved ILS glideslope antenna for the GNS430W?  It seems like the COMANT CI-193 might be, but I’m not sure.  Can anyone provide any help on my options? Thanks!

 

 

 

Edited August 9, 2025 by Targhee

[N201MKTurbo]

Do you have nav antenna coupler that splits the nav antenna to the two nav receivers? They usually have a GS port. If not, a new coupler with a GS port is cheaper than a GS antenna.

https://www.chiefaircraft.com/aircraft/antennas/couplers/as-av571.html

 

[PT20J]

The Garmin installation manual should list approved antennas.

[N201MKTurbo]

FWIW, the GS frequencies are the third harmonic of the localizer frequencies. That is why you can get away with using the nav antenna for GS.

[EricJ]

The GNS430, etc., may list a TSO for the antenna requirements, in which case any antenna meeting the TSO will be compliant.   Otherwise check with your IA, as it wouldn't be unusual to just find a suitable GS antenna and plug it in.   For the most part the receiver won't know the difference.

[rklems]

A diplexer attached to your nav antenna should work great like @N201MKTurbo mentioned. If you don’t already have one, I have a whole bunch of used ones (most modern radios take the combined nav signal and do the signal splitting internally, so I remove a lot of them and just use full signal splitters)

[Aerodon]

On 8/8/2025 at 7:48 PM, Targhee said:

I have a G600/GNS430W in my M20J.  The antenna wires on the King KA-22 glide slope antenna (mounted inside the windshield on the center pole) wires broke off when a maintenance shop pulled the sun shield off.  Now I can’t get an ILS glideslope.  I can’t seem to find a used King KA-22 anywhere.  Is there another approved ILS glideslope antenna for the GNS430W?  It seems like the COMANT CI-193 might be, but I’m not sure.  Can anyone provide any help on my options? Thanks!

 

I have one of those CI-193 antennas for you, one with a little tab that can be used to mount to a round tube.  Another option is to use your existing VOR antenna with the correct splitter to go to your two nav receivers.

Use the opportunity to replace at least some of the coax.

The separate GS antenna provides a better GS signal, less line of sight shielding and less 'splitting.  

Aerodon

 

 

[EricJ]

2 hours ago, Aerodon said:

The separate GS antenna provides a better GS signal, less line of sight shielding and less 'splitting.  

Yes, there's a little loss in the splitter/diplexer to both the GS and VOR receiver, which can be avoided with a separate GS antenna.   As you mention, careful placement of the GS antenna might make it better than the VOR antenna...on a Mooney, maybe. 

It's all tradeoffs, but it's good that there are options.   If the GS is in good working order it will likely not make much difference which approach is taken since those systems generally have a lot of design/link margin.   A splitter/diplexer will cause a little bit of range reduction to a VOR receiver, though.

 

[Aerodon]

And newer receivers are probably much better than old.  I would try removing that GS antenna completely and putting in th appropriate splitter and giving it a try.

 

Don