Radio problems

I've been working an ongoing radio problem and thought I'd throw it out here to see if anyone has any ideas. My RV-8 has a icom A-200/A210 and a flightcom 403 intercom. Over the last year I started having intermittent problems with transmitting...reception has always been fine. At times it works fine, at times it will not transmit at all, at times it will transmit very brokenly with the TX indicator flickering. Several months ago I pulled the radio and cleaned all the contacts in the back of the rack as well as checking grounds, etc. It seemed to work better for a few flights, but the problem returned. Last week I bit the bullet and upgraded the radio from the A-200 to the A-210 in the hopes that the problem was internal to the radio, and what the heck, I liked the upgraded features on the new radio (I know about the ribbon issue). Anyway, in the hanger the new radio seemed to be working great. I pulled the aircraft out of the hanger, copied down the ATIS, started up the engine, and went to call for taxi and the radio would not transmit. Well at least I've eliminated the radio itself as being the problem! Last night I ordered a few new connectors for the RG-58 coax and will see if that might help. I'd be a little more confident if it wasn't receiving just fine. The intercom seems to work fine. When I push the PTT, if it transmits I will hear my voice back through the intercom...when it fails to transmit it will mute my voice. Clearly the PTT button is triggering the intercom. Any thoughts? Is it possible that a faulty antenna (or connection to the antenna) will receive fine while failing to transmit correctly? Thanks in advance for any advice!

Mark

Yes--Clear pouch

Check all of your antenna connections and the RG58 cable along it's length for cuts. Receiving is the easy part. Transmitting brings a whole lot more dynamics into the fray. Sounds like you have some pretty high SWR when transmitting which could be caused by the antenna cable, antenna, or even corroded connectors.

Vic

Bad ground

The PTT switch applies ground to the tip of the pilots mic jack. My guess is the PTT is flaky or a bad connection at the switch, the mic jack tip or pin 24 of the A210 connector.

You need to watch the T in the radio, it tells you a lot. If it is not lighting up and not xmit then its a PTT problem. I suspect a wiring problem since it worked fine in the hangar and the stopped with the engine running. (vibration)

Jay

Very likely the relay contacts in the 403MC. (they close when you key the PTT to connect the mic to the radio).

Turn off the radio and key the (intercom) mic a dozen times (wipe the relay contacts a bit), then turn on the radio and see if you are heard when you TX.

(I'm living this issue now, but the passenger can't hear me until I key a few times)

BTW, I'll take your A-200 in exchange for this helpful advice

Papa said:

Over the last year I started having intermittent problems with transmitting...reception has always been fine.

Click to expand...

Clue #1 - Intermittent and getting worse.
A connection is failing somewhere.

Papa said:

At times it works fine, at times it will not transmit at all, at times it will transmit very brokenly with the TX indicator flickering.

Click to expand...

Clue #2 - TX indicator flickering.
When the TX indicator is off the radio is not transmitting. If the TX is coming on then off, the transmitter will be coming on then off resulting in broken transmissions.

Papa said:

Last week I bit the bullet and upgraded the radio from the A-200 to the A-210... I pulled the aircraft out of the hanger, copied down the ATIS, started up the engine, and went to call for taxi and the radio would not transmit.

Click to expand...

Clue #3 - Same problem with new radio
Highly doubtful 2 radios with same internal problem so back to clue # 2

Papa said:

At times it works fine, at times it will not transmit at all, at times it will transmit very brokenly with the TX indicator flickering.

Click to expand...

Clue #2 - TX indicator flickering.
Transmit is controlled by PTT "circuit" which has no effect on reception. The PTT "circuit" includes the PTT switch, the intercom, the radio(s) and all the wires connecting them together. Do you have a second radio? Does it have the same problem? If only 1 radio, can you bypass the intercom and see if the problem goes away? If yes, then bad intercom. If problem continues then check the PTT switch, the wiring and all the connectors.

Last resort, take it to a good avionics shop. Good luck. Problems like this one are a PITA to find.

A friend had a similar issue on his -4...

It turns out that he was using auto spade fuses. The connections had gotten cruddy and he had problems transmitting. He cleaned the contacts and put in a new fuse and the problem went away.

Thanks all,

At this point I'll try to re-clean all the connections and replace the BNC connectors on the coax this weekend. I also wrote the flightcom folks to see if they had any suggestions regarding the 403. Clearly the radio itself is not the problem. I'll post my progress as it happens.

Mark

You didn't mention what antenna you were using. I have gone through the same radio upgrade path as you and am using a Comant bent whip antenna.

At one point, I had the same issue as you. My solution was to remove one screw at a time and give each screw hole a couple of turns with my deburring tool and a dab of dialectic grease before reinstalling the screw.

Also using a comant bent whip. Something else to explore.