Help me diagnose a problem...

[AlleyCat67]

Dear POA braintrust...

Recently we upgraded the avionics on our Tiger, and went with a GTN 650 as GPS/Nav1/Com1, and a dual G5 install. We're still using the old Narco MK12D as Nav2/Com2. The 650 talks to the G5 HSI, and the Nav2 talks to an old Narco CDI/GS indicator.

After a couple of test flights, it's clear that the glideslope does not come alive on the G5 during ILS approaches, although the localizer works fine. On the same ILS approach, both the glideslope and localizer do come alive on the Nav 2 indicator. In contrast, on an RNAV LPV approach, the glidepath indicator works just fine on the G5.

Any ideas where the fault likely lays (before I call the avionics installer)?

 

[Ravioli]

Any ideas where the fault likely lays (before I call the avionics installer)?

It's probably right where the installer finds it when they fix their work.

[No guy on the internet knows the full installation]

 

[Jesse Saint]

I’d be willing to bet I know where the problem is. You probably had another similar Nav radio as your current backup as your previous backup, but without glideslope. Your MK12D was primary before with glideslope. If this is the case, then the problem is in the triplexer.

A diplexer splits the Nav antenna signal into a glideslope and a VOR/loc signal. A triplexer does the same, but it sends a second VOR/lic signal for the second Nav that doesn’t have a glideslope. The GTN gets a single input and it diplexes the signal inside. If it’s going through the triplexer, then the GTN is only getting the VOR/loc signal with the glideslope removed. You’ll need to add an antenna splitter to split the full signal, then send one full signal to the GTN and then diplex the other full signal to split it up for the MK12D.

 

[Radar Contact]

I’d be willing to bet I know where the problem is. You probably had another similar Nav radio as your current backup as your previous backup, but without glideslope. Your MK12D was primary before with glideslope. If this is the case, then the problem is in the triplexer.

A diplexer splits the Nav antenna signal into a glideslope and a VOR/loc signal. A triplexer does the same, but it sends a second VOR/lic signal for the second Nav that doesn’t have a glideslope. The GTN gets a single input and it diplexes the signal inside. If it’s going through the triplexer, then the GTN is only getting the VOR/loc signal with the glideslope removed. You’ll need to add an antenna splitter to split the full signal, then send one full signal to the GTN and then diplex the other full signal to split it up for the MK12D.

Jesse,

I don't have a dog in the hunt and hope that helps fix his problem. Just wanted to say thank you for your contributions here. I learn something from most (if not all) of your posts.

 

[AlleyCat67]

I’d be willing to bet I know where the problem is. You probably had another similar Nav radio as your current backup as your previous backup, but without glideslope. Your MK12D was primary before with glideslope. If this is the case, then the problem is in the triplexer.

A diplexer splits the Nav antenna signal into a glideslope and a VOR/loc signal. A triplexer does the same, but it sends a second VOR/lic signal for the second Nav that doesn’t have a glideslope. The GTN gets a single input and it diplexes the signal inside. If it’s going through the triplexer, then the GTN is only getting the VOR/loc signal with the glideslope removed. You’ll need to add an antenna splitter to split the full signal, then send one full signal to the GTN and then diplex the other full signal to split it up for the MK12D.

Jesse - you may well have nailed it. Yes, we originally had another Narco as Nav2 without a glideslope (now removed). I'll ask our avionics guy about the possibility of adding an antenna splitter. Thanks!