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Strange radio transmit problem - any suggestions?

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peter(at)sportingaero.com
Guest

Posted: Wed May 12, 2010 12:22 pm Post subject: Strange radio transmit problem - any suggestions?

Hi, 

 

 I have a Becker AR4201 radio in my One Design that I have just started flying (2 hours on the tacho). Initially the radio worked great (after I got the mike jack wiring correct - there's always one bozo moment in any project). Halfway through the 2nd flight the transmit quit - receive was still good. Plugging in another headset on the ground and the transmit worked OK.

 

 A couple of days later I pushed the aeroplane out for another flight and no transmit at all. Carrier wave is being transmitted but no modulation (and so side tone in my headset). After trying to figure it out for an hour I put it back together and went flying, still with carrier wave only. After a while I called a local tower (119.0) - loud and clear. Returned to my field (124.1) to the same problem - carrier wave only. What is going on!!!  

 

 I have not been able to test further - but I need to step through the frequency range and find out which freqs work and which do not. This is a very simple airplane with no intercom, headset connected directly to the radio. Receive is good all the time, on all freqs tried so far. Radio shows the transmit arrow whenever the PTT is pushed, and puts out carrier wave on 124.1. Why is it modulating on some freqs and not others? Headset works in other aircraft (have tried 3 so far with same results).

 

 Does anyone have any idea about what is going on?

 

 Any suggestions gratefully received.

 

 Peter    [quote][b]

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skywagon

Joined: 11 Feb 2006
Posts: 184

Posted: Wed May 12, 2010 1:47 pm Post subject: Strange radio transmit problem - any suggestions?

Peter,

 From your description...no modulation is happening.   Kinda' points to the microphone cartridge or wiring in your headset is randomly  malfunctioning.  Since you can plug another headset in and all works well,  it points to the mike subassembly in your headset.  The wiring inside most  sets is really tiny stuff.  Maybe the wire has broken inside the insulation  and makes contact only when your head or mike boom is in a certain position and  then, the wire opens in other positions.  Check it closely and carefully  flex the wiring and see if you can find it.  Using an ohm-meter is probably  the easiest tool to see if a break is present.

 If the mike cartridge is bad, the manufacturer has to send  you a new one or you send the headset back in with a detailed  note describing the "randomness".  Of operation.  

  

 I once had a David Clark set that developed a failed  speaker element.  Called DC and told them the problem.  Guy on line  said, "...that's impossible.  We've never had the earpiece element  fail".  I had to do some tall talking to convince him to send me a new  one.  He did with my promise to send back the old one.  He later  called and softly apologized.  The element had indeed, failed some way  inside the unit.

 David

   

 [quote]   ---

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user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Thu May 13, 2010 6:01 am Post subject: Re: Strange radio transmit problem - any suggestions?

Peter,

I have learned that assumptions are often incorrect while conducting experiments under intermittent failure conditions.  Do not assume that nothing is wrong with your headset just because it worked in other aircraft.  Try another known-working headset in your One Design for several hours.  If there are still intermittent problems, there could be a bad connection at the mic jack or at the connector on the back of the radio.

Joe

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