Radio Troubles

OkieFlyer

OkieFlyer

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Joined
May 16, 2011
Messages
3,225
Location
Lindsay, OK
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Display name:
Andrew L.
Hey guys and gals. I posted this in the maintenance bay, and didn't get any replies. I hate to be redundant, but I was hoping the higher traffic volume here in good ol' Flight Following might help me catch someone who can help. So here goes.

First, a description of my setup: Narco MK-12D Nav/Comm, Narco CP-136 audio panel, PS Engineering PM1000ii 4 place intercom, pilot only PTT.

What's going on: Intercom works fine. I can hear myself and passenger clearly in the phones. Once I key up to transmit over the radio, I can no longer hear myself in the phones. Another pilot reported to me yesterday after my flight that he could hear me loud and clear, so I'm transmitting just fine. However, I was unable to hear any of his transmissions and was unable to hear ATIS. When I let off of the PTT I do hear the typical momentary fuzz sound that most radios make. Also, with the comm panel set to "speaker", I can hear a click when I key up and when I let off the PTT. So it acts like it's doing something.

I'm not sure how my gear is wired up, so I don't know if the problem is in the radio, or perhaps wiring from the radio to the intercom, or wiring from the radio to the comm panel, comm panel to intercom, etc. I suppose I'll just have to get under there and see how it's all rigged up, but I was hoping that someone has had this kind of issue, and can point me in the right direction. Not that it matters when it comes to electronics, but I've had no other issues leading up to this. It worked fine on all previous flights. Let it be known that electronics is not my strong suit, but I'll dig in as deep as is necessary to save a nickel ;)

If you can offer any guidance, I would greatly appreciate it.

-Andrew-
 
Is there any chance the radio volume control is turned down? I only ask because that has happened to me before. If it's not a knob turned down, it could be a disconnected wire from the radio receive audio signal to the audio panel. That would cause your side tone and receive to be silent but not interfere with intercom use and transmitting on the radio. The squelch break you hear when you key and release the PTT could be the audio panel switching you to the radio and back rather than from the radio itself.
 
Thanks for the reply. Thankfully, I had my wits about me and checked the volume knob. I fiddled with everything I could fiddle with from the outside. Volume, squelch, comm1/2 and speaker switches, cycled the breakers, cycled radio power, changed headsets, tried headsets in other sockets, intercom ISO, talked to it sweetly, caressed it, basically anything that can twist or toggle. ;)

I've got an annual coming up later this week, so I'll be able to get behind the panel. I just need to gather some insight from the POAers so maybe I can make heads or tails of what I find back there.
 
I've exhausted my knowledge with the volume knob. Here's hoping it's a loose wire that your annual turns up immediately and not an actual problem with the radio. Occam's razor says loose wire but Murphy's law says that Occam was a naive fool. Good luck!
 
Capt. Geoffrey Thorpe said:
So, no audio output from the radio?
Click to expand...

Well, none getting to my phones. Without knowing how things are wired up, I don't know if there is no output from the radio, or if the radio is outputting and the problem is somewhere between the radio and my phones. Does that make sense? Would the radio's output go through the comm panel, and then through the intercom before it makes it to me? Or perhaps the intercom is bypassed when the radio is in use? Is there a fairly standard way in which radios, audio panels, and intercoms are interconnected? If so, it might help me narrow the search.

I would say that it's possible that the radio is unable to receive, but that wouldn't have anything to do with me not being able to hear myself when keyed up, would it?
 
Yes, it makes sense to me that the problem is audio out and not receiving. Whether it is the radio itself or a connection between the radio / com / intercom, I wouldn't have a clue.
 
Capt. Geoffrey Thorpe said:
Yes, it makes sense to me that the problem is audio out and not receiving. Whether it is the radio itself or a connection between the radio / com / intercom, I wouldn't have a clue.
Click to expand...

I reckon there's no way for anyone to know until I go digging into it. I suppose I was just hoping this was an "ol' Narcos are known for (insert issue)", kind of a thing, and someone would have a fix for it. Haha. It almost never works that way, but I can hope. ;)

Thanks, man.
 
I'm a bit late answering this, but I just bought a Cessna 172C with a Narco CP 136 that has the same issue. Saturday I talked to Pat Rhodes of East West Avionics in Honolulu. He told me the problem is that Narco radios have two audio outputs, one for receive and a second for sidetone (the audio you hear when you transmit). No one else does it that way. All other radios have only one audio output. So to use other radios with the Narco audio panel you have to get the pinout for the audio panel, find the inputs for #1 radio audio and #1 radio sidetone and splice them together. Same for #2.
I'm hoping to do that with my plane shortly.
 
edit: i re read what you wrote, its either a broken wire to the intercom, or a radio issue. find a radio you can pop and swap to check quickly and easily, i bet its the radio
 
get a buddy with a handheld, or someone with another plane you can do a radio check with very easily. lets you know right away if the radio is transmitting with no side tone, or doing nothing on the output side.
 
Sidetone has failed. Troubleshoot that. The radio sounds from your initial description like it works just fine. Pilots are just used to sidetone and hearing themselves.

You don't have to, and many radios "back in the day" didn't provide it and it didn't matter other than you couldn't hear if you had badly misplaced the microphone so much that you are too far away from it and quiet, or have it too close and are muffled or distorted.

Learn where to put the mic and you don't need it at all.

But if you're going digging in an old radio and panel, what you'll be looking for is the radio to produce sidetone output and see where it dies as you work your way away from the radio and toward the headset.
 
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