Radio

[B19]

Been having problems with Com radio. Works fine, take off fly for an hour, lately half the time I return to airport tower says the only thing they hear is a carrier signal or a broken signal. After I park, I play with connections call ground and everything is fine. I have Garmin PTT switch and Flight com intercom, Narco 12 D radio. Can anyone give me best way to troubleshoot problem.


Thanks
Bill B (B19)
Juneau, Alaska

[TURIN]

What does the AMM, FIM/TSM say?

[Hasherucf]

Narco of course are no longer supported. Normally when the displays go its game over as you cant get parts.

If it was me I would put the narco on the bench and let it run. Give it a few calibrated whacks and try some freeze spray. I am guessing it gets cold at altitude there. It may be that something is heating up and causing your U/S. Failing that you have a loom you can put the aircraft on ground power and let it warm up, make some calls to a relatively distance station.

I always do a VSWR check and if you can get 2 its great but 3 is acceptable.

Load test the Circuit Breaker to the radio a 22 ohm resistor in series with the multimeter and see if you get a voltage drop. If you do its the CB. These older radios dont seem so voltage sensitive as say the microair

Check corrosion on the pins and there tension. Also that its racking correctly. Also the screws in that back of the rack are present

Normally when flightcoms go its obvious from the start so I'm thinking its in the Narco.

To be honest if that's the problem junk it and get a SL40 or Icom. Fixing them is a false economy.

You mentioned you play with connections. If its the jacks they can lose tension on the prongs. Also if you have left the aircraft sitting corrision can build up on the jacks. A bit of scouring pad cleans it up but if so then replace jacks.

I guess you have a switch panel so check there for dry joints.


Ok thats a lot but hey good luck.

[glendalegoon]

try a brand new/different microphone...bring it along with you and when you get the call: carrier only, no voice modulation

plug in the different mic and see what happens.

[B19]

Flying in South East Alaska is a little different than the lower 48. I have been doing regular radio checks on 122.9 and the range of the radio is good. Say 90 miles at 3500 ft. modulation good until the problem arises. Carrier only, I am guessing the signal strength is good, just no voice.


As far as I can tell there is a transmit relay, I am not sure how it interacts with the intercom and push to talk switch and radio. Been looking for circuit diagrams will little to no luck as to what is in the plane.


I will clean plugs,and inspect all connections. The next time I fly I will bypass the intercom, to see if problem returns.


The plane is parked outside, lots of rain here, corrosion is always a concern. We don't have an avionics shop in town, so you have to sent radios and such out for testing.


Thanks for your input, good things to think about


Bill B

[MC5Wes]

If it works great at the airport. But starts to fail the farther you get away. Take a look at the antenna.

[Lear_doctor]

I assume you have resolved this by now, but here are some thoughts. The tower can 'hear' your carrier wave transmission (or broken audio), so the problem appears to be a loss of MIC audio. The signal for the audio I suspect travels from the MIC in your headset, though the headset connection, to the intercom and from there to the appropriate radio for transmission (the Narco in this case), from the IC it arrives at the Narco and inside that unit the MIC audio is added to the carrier wave and heads off into the ether. Somewhere along that path you have a break.


To start - If you can hear your own voice without any breaking up etc. over the intercom you can assume the headset and the headset sockets are good (they are common to the radio transmission of course), that means you need to look more at the Narco or the connection to it from the I/C.

Another quick check, you did not mention whether you have a P2 position, can you plug yourself into that and transmit from that side when your experiencing the problem? - That MIC audio will be a different input to the I/C and may work better if that P1 channel of the I/C is intermittent in operation.

Once again not sure of the unit itself but if you have an emergency position on the I/C then try that when the transmission issue is occurring, that will essentially pass your audio through with the most basic of addition from the I/C and if that improves matters then your I/C must be suspected.

After that lot your down to the Narco and there is not a lot you can do with that other than borrow someone else s for a flight if that possible. With the Narco extraction PIN they are very easy to remove and install.

All the best

The Doc

[B19]

Plane is in for annual right now changing #1 cylinder, just ordered a new antenna for com 1. I hope to have this work done by end of December. I will be going through the radio, and hopefully find what is causing my problem.


I am sure the problem is simple but finding it is time consuming, considering it works most of the time.


I may change the intercom as it was installed when I bought the plane almost 20 years ago.


When the problem occurs I am coming into land and I just fly the plane not a lot of time to troubleshoot.


Next time I fly I will contact Juneau radio outside controlled airspace, let the wife fly while I do more troubleshooting. My #2 com works but again its an old king KX170B and I have been told transition has static.

[TinyTim2]

Not sure the antenna will have any effect on modulation! Could be a waste of money ........unless the reports of carrier only are mistaken !

[B19]

Do I have the operation of the microphone correct? There are 3 connections on your microphone.


-The tip contact is for push to talk. This is a power line. When grounded tells transmitter relay inside radio to switch from receive to transmit. The microphone diaphragm also uses this power.
-The middle contact (ring) is the audio out and is sent to the pre amplifier in the radio which is voice we here on the other end
-The base or(sleeve) contact is ground used by microphone and is the ground for the push to talk switch that activates the transmit relay in radio


So if I am sending a signal out with no voice that means there is bad connection in the middle or (ring) contact or wiring?

[B19]

OK, this problem bugs me. Today I checked all connections, wiggled wires while transmitting and listening on a handheld. Could not get to fail. Radio was on over 2 hours.


Tower said there was no audio but had a carrier signal.


What am I missing??

[Lear_doctor]

You say you wiggled wires etc and listened on a hand held. What was the result of the hand held test? could you hear your transmission clearly? - If you can hear your transmission on a hand held that is obviously close to the transmitting antenna then the issue is not loss of MIC Audio but a loss of range.

This means one of three things normally

1. Low output power from the transmitter (the radio)
2. A poor VSWR (antenna system quality if you like), this can be the antenna itself, of even the co-axial cable that runs from the radio to the antenna. Poor matching between the antenna and the radio is ensuring most of the power is being lost. A tech can test the VSWR from the radio tray and check this number for you if needs be, the antenna specification will be on the internet, but in essence your looking for less than 2:1. You can also use a thru line Wattmeter to measure power if needs be, clearly this should be close to the output power as specified by Narco for the unit.


Assuming you cannot hear your transmissions - see my post above

You have positions P1 and P2, is the fault apparent when you transmit from either side?

Can you hear yourself when transmitting (sidetone)? if you can then you can be assured your voice is at least reaching the intercom.

Let us know the answers to the above questions


regards

The Doc

[B19]

Hi Lear Doctor


I had a chance to fly yesterday. Was checking out the radio and the #1 cylinder I had just replaced. Just did pattern work.


Everything went well. I took the intercom out and just used the PTT switch.


I will continue to trouble shoot, and try what you suggested.


Thanks for your thoughts
Bill B (B19)

[MC5Wes]

It might help if you listed the equipment you have installed. Also do you have two radios and only one is bad?