Experiences with Garmin GTR 225

In case anyone is looking for a starting point from which to fine-tune the squelch on a GTN650, COM RF squelch set to 40% works OK on mine with Main software 5.13 and COM software 2.20.

The carrier noise squelch level is ideally at about 1.5uV soft 30% @ 1Khz modulation level

Not sure if the unit has a carrier level squelch setting / adjustment but if so should be around 6uV soft @ 85% 8Khz modulation level

With climax / offset carrier transmissions from ATC if the carrier level squelch is incorrectly set it will result in a loss of reception of ATC calls, although other aircraft will still be heard, this can be very confusing!
I see a lot of comm’s that have been incorrectly set I always check them as a matter of course, I imagine that 8.33 Khz channel spacing may further effect reception on 25 Khz units

There is no test for this on a radio annual, indeed the ramp gear cannot generate the required signal!

Narco COM-810 /811 and the ICOM A200 units have a design defect that can cause the ATC issue, both companies were told Narco authorized a mod to cure the problem Icom showed no interest

Simon wrote:

so check you have the latest software installed

I certainly haven’t, and it’s on my todo list to upgrade. I ended up turning up the squelch level in the setup menu, but that seems to come at a loss in sensitivity…

There have been some software issues to deal with the squelch levels on Garmin units so check you have the latest software installed

I had the same problem – my GTN650 used to break COM squelch all the time like a Labrador fed on beer and chick peas. I fixed it by going into setup mode and adjusting the squelch level. Then one of the recent software updates addressed the same problem, so I reduced the squelch a bit. It’s good now, so if anyone is interested I’ll check what level I ended up with.

USFlyer wrote:

He asked about the GTR225, not the navcom radio.

I know, thanks, I can read. But since these radios are very similar (the GTR225 is the GNC255 without the nav part).

tomjnx wrote:

GNC255 as #2 radio

He asked about the GTR225, not the navcom radio.

alioth wrote:

but has anyone used one?

I have a GNC255 as #2 radio. So far it works pretty well. Viewing angles are not limited by the display. The two minor nitpicks I have with the radio is:

• Garmin radios generally (applies to the GTN650 as well) seem to have worse squelch circuitry than Bendix King

• The GNC255 drives an old KNI520 indicator. The glideslope flag of this indicator wasn’t used before, so got a bit sticky. In the beginning, the GNC255 not always managed to get the glideslope flag out of sight, while on the bench with a lab power supply and appropriate series resistance it worked. This has by now fixed itself, but it seems like the GNC255 flag output is a bit low.

alioth wrote:

GTR 225 would be a really nice option

I have the GTR 225 in my Flight Design CT. The LED display can be viewed from any angle and there is a photocell that dims the display automatically for night flying.