Project Corner – Dan’s Radio

Tech Counselor Dan Masys writes:

In the spirit of “once a project, always a project” I was noticing that my RV-10’s 14-year-old Garmin SL40, functioning as Com 2 in the radio stack, was getting weak reception and losing functionality such as not having an effective volume control knob.

RV-10 panel with SL40 Com2 in middle of the center stack.

I also noticed that minimum charges for bench testing a Garmin avionics unit and doing any out of warranty repair work are approaching or even exceeding the value of the unit. (Lemmee see, do you think that might be by design?)
With the writing on the wall, and always looking around for a useful upgrade, I opted to pull the SL40 and its tray out of the stack, and replace it with a new Garmin GTR 200 transceiver from Aircraft Spruce.

The only connections the new unit needed were the external antenna, power, ground, and five wires going to the audio panel. Fabricating a new wiring harness was made relatively simple by the fact that during the original build, I had positioned in-line connectors (DB9 or DB25 computer connectors, to be exact) in between all avionics in the stack and all other units. So it was only necessary to terminate the new wiring in a DB9 connector that matched the pinouts of the original wiring. A side benefit of just keeping the old unit, its tray and its wiring, is that it can simply and easily be re-installed if needed. (ie., nothing about the old radio, its tray, or wiring harness was altered in installing the new one.)

A bonus of having the new unit is that it has a 10 watt transmitter vs. 8 watts for the old one, and a much more informative digital display e.g., when monitoring two frequencies at once, it shows which one is receiving a transmission at the moment.

A minor annoyance was that Garmin radio trays apparently now are just a smidge wider than they used to be. The standard 6.25 inch width has now become 6.30” – just enough that new trays won’t slide easily into stacks of older radios without some creativity with a flat file to make the opening a bit wider. Luckily the height of the GTR200 is the same as the SL40 (even though the Garmin specs say it isn’t!) so neither the GNS480 navigator above the radio or the GTX330ES transponder below it had to be moved.

Oh, and the new unit works great. : )