Becker AR4201 Transmission Problem

[RMM-Guam]

Just purchased a used aircraft with a 5 year old Becker AR4201 radio that seems to work normally BUT no sound goes out on transmission. Previous owner says everything was fine prior to my purchase of the aircraft. No changes made. I am using the previous owner's Bose headsets. So I can understand the wiring was done correctly on initial installation.

The PTT click can be heard on the hand held radio opening the frequency, but no sound of the voice transmission is transmitted to the receiving handheld radio. Black triangle on top row shows the radio is transmitting. But no voice is coming through. Tried two different working headsets, one is a friends and is brand new. Same situation.

All functions on screen are normal. No error codes. Receives transmissions from the handheld radio and also receives the ATIS loud and clear.

What am I missing?

RMM

 

[weirdjim]

Just purchased a used aircraft with a 5 year old Becker AR4201 radio that seems to work normally BUT no sound goes out on transmission.

Does that mean carrier but no audio or no carrier at all? A handheld at one end of the runway with the aircraft on the other should tell you whether or not there is carrier.

Previous owner says everything was fine prior to my purchase of the aircraft. No changes made. I am using the previous owner's Bose headsets. So I can understand the wiring was done correctly on initial installation.

I would not presume that.

The PTT click can be heard on the hand held radio opening the frequency,

What does that mean?

but no sound of the voice transmission is transmitted to the receiving handheld radio.

How far away is the handheld.

Black triangle on top row shows the radio is transmitting. But no voice is coming through.

What is a black triangle and where is the top row of what? All a "transmit" light shows (*) is that the PTT switch has been pushed and the radio has gone from the receive to the transmit mode. It says nothing about whether or not the radio is actually transmitting.

An exception to that is the 1950s-era Superhomers that actually used some of the RF transmit power to light a small incandescent light on the front of the radio and you could see it glow bright and dim in time with your voice.

Tried two different working headsets, one is a friends and is brand new. Same situation.

All functions on screen are normal. No error codes. Receives transmissions from the handheld radio and also receives the ATIS loud and clear.

What am I missing?

Well, from your description above, I'd say you are missing the transmit function

RMM

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[denverpilot]

Start simple. Check the headset, jack, and PTT by moving over to the right seat. Sounds like a busted audio path between headset and transmitter. That doesn't do it, eliminate things one at a time...

 

[RMM-Guam]

Today, after curing a ground problem with the antenna end connector, we were able to transmit on frequencies from 127 to 136. So we know the wiring is ok, but the radio won't transmit from 118 to just below 127. According to another case, the radio is not at fault and the solution is to upgrade the cable and re-crimp. So this will be the next step.

 

[RMM-Guam]

Hey Jim...
Thanks for the careful attention to my description. What we knew was the PTT click was heard on the handheld radio from various distances, but no voice was carried. So the radio was opening the frequency but not putting the audio through. Now we know everything works but some frequencies are not transmitting. If you have a suggestion on that, please advise.
RMM

 

[SCCutler]

I will be fascinated at what failure exists that allows transmission on certain frequencies, and not on others, and resides outside the radio itself. I am skeptical.

 

[weirdjim]

I will be fascinated at what failure exists that allows transmission on certain frequencies, and not on others, and resides outside the radio itself. I am skeptical.

Well, if it really is an antenna problem (and I, like you, am skeptical) then some transceivers are built with what is called "VSWR protection". If the antenna is really honked up in a way that lets it be "good" (whatever that means) at the high end of the band but is so bad at the low end that the VSWR shutdown completely turns the output stage off to protect the output transistors from french-frying themselves then you will see what the OP observed. HIGHLY unlikely.

Most folks, before they go all aflutter and start replacing coax and recrimping (which, by the way, is impossible) would put a proper dummy load on the output of the transceiver and THEN see if it transmits over the whole band. You can make such a device for a quick and dirty test by bunching together a dozen 560 ohm half watt carbon film 2 cent resistors with VERY SHORT LEADS and using this in place of an antenna. That would pretty well prove transceiver or antenna quite economically.

The classic way of doing it in the field is to take the tinned lids from a couple of soup cans and drilling holes in a small pattern in both and sandwiching the resistors in between the lids. Then solder coax to the lids and there you have it.

But the alternative is to start replacing parts willy-nilly until you find one that fixes the problem. In the biz that is called shotgunning and is frowned upon by those who know what they are doing.

Jim

 

[RMM-Guam]

Today we used a second antenna. The transmission problem was replicated. I called Northern Lights Avionics in Alaska. They immediately said the radio needs repair. Becker USA says the problem lies in the modulator board and with labor could be $1,000 plus two way shipping. Ouch!
Thanks for taking time to offer ideas and guidance.
Very much appreciated.
RMM