Quick checks for radio reception

[Quint Van Deman]

Fellow Comanche owners--

I've got one of those panels that would make most flyers cringe...2 radios that are both at least 40 years old with wiring to match, and for the icing on the cake, a home built 40 year what seems to be home built audio panel.
When I bought N7406P radio #1 was a strong receiver, but transmit was so weak I only consider it the "weather radio". Radio #2 was a pretty good all around, with no complaints on reception or transmission. Full replacement was on the 5-7 year plan, but not in the immediate budget (which is being spent on powerplant/airframe items). Everything was going to plan until reception on radio #2 started to get flaky...now I'm tuning both radios to the same frequency to ensure I don't miss anything (receiving on #1, transmitting on #2) and realizing just how ridiculous and potentially dangerous that is going forward.

Which leads me to my question: I'm about to take her in to have an avionics shop look things over, but are there any "stupid checks" that I should do before spending $90/hr? Dirty antennas? Easily checked connections? I'd really like to get just a couple of more years out of these radios, but I also don't want to sink tons of cash chasing gremlins in antique equipment.

Thanks for any tips,

-Quint

[Pat Donovan]

HI Quint,

Assuming the radios are the same, the first thing I would recommend is swapping the radio positions to see if the symptoms change with position. The second thing I would do is check all connections. You can use a pencil eraser to clean off any oxidation. Don't forget the connections at the antenna location. Lastly, be sure to check for any corrosion at the antenna base to ensure you get a good ground plane.

Good luck,
PatD

[md11flyer]

Quint: The easiest thing to do is to swap radio 1 with radio 2. That is assuming they are the same model radios.
That way you can get an idea if the symptoms of the radio (week transmission) follows to the other radio tray then you can almost be assured that the problem is in the radio itself. If it doesn't, then you can suspect a problem with the wiring/ antenna. Also if you know somebody that has the same radio as you have and he will loan it to you for a test flight you can rule out the problem that way.
If not its not all that bad paying the 90 dollar per hour to a reputable shop to diagnose the problem. They have testers that will test your coax cables to rule out those as the problem and they can tell within minutes of hooking the radio up to their test equipment as to the serviceability of the radio.
Just an aside, sometimes all the problems go away just reracking the radios. (I remember back 25 years ago doing my initial instrument check ride where during the ride the vor/ils just would not pick up signals beyond 4 miles of the station. To my surprise the inspector had me hod at the NDB and he pulled out his allen key and reracked the number 1 nav com, after which the ils/ vor worked like a charm.
If you have the old KX170/175 you can get the slide in replacement of the digital version of this reliable radio for around 750 dollars used. Most avionic shops have these around from panel upgrades. Off the top of my head I believe its the Mac 1700 unit.
Its still going to cost some dollars but when you upgrade the panel later you can use that one as your number 2.

Gary

[Quint Van Deman]

Pat/Gary--

Thanks for the tips. Unfortunately the radios aren't identical...they are both TKM's, but one is a MX-12 the other a MX300, one of the two is removable with just an allen wrench to the front, the other unfortunately is secured from the rear, a costly configuration I dealt with once before when it blew a fuse on a hot day. I will pull & reseat the one that's accessible, otherwise it sounds like my original plan (into the shop) is probably the way to go.

Thanks,

-Quint