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Noise in Handheld Tx signal

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lrsecaldwell(at)earthlink
Guest

Posted: Mon Mar 08, 2010 5:37 am Post subject: Noise in Handheld Tx signal

[quote]As is frequently the case, once you truly identify the root cause of a problem the solution is obvious.

In this case we were using an external headset with the A24 hand held without an external PTT.  In other words we were using the hand held Tx button for the PTT.  The owners manual did not say if the external PTT was either recommend or necessary with an external headset.

After discussing the problem with ICOM tech support they told me that when you press the hand held TX button it connects the internal mic as well as the external mic to the transmitted carrier.  Consequently when we tried to transmit without the engine running the Tx signal was reasonably quite but with the engine running the mic in the hand held picked up the cockpit noise and transmitted it along with the voice from the headset mic.

Correction of this problem was easy we just used an external PTT.  Just one more wire in the cockpit

I suspect that this may be common to other handhelds.

Roger

Time: 04:54:24 PM PST US

From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

Subject: Re: Noise in Handheld Tx signal.

At 06:51 PM 2/28/2010, you wrote:

    	  Quote: 	
		  >Caldwell" <lrsecaldwell(at)earthlink.net>

 	  Quote: 	

We have a problem with excessive noise occurring in an ICOM A24.

Receive is good.  The noise only occurs in the transmitted signal 

while the engine is running,   The noise is so bad the the voice is 

not understandable.  If the operator is about 100 ft from the A/B 

with the engine running the noise is down to a level that is acceptable.

    	  Quote: 	
		  >Th hsndheld is completely independent of the a/c.  Internal 

 	  Quote: 	
		  batteries and operation on the rubber duckie antenna.  A headset  is 

used.  Two different A24's with different headsets exhibit the same problem.

There are no avionics in the plane except for the handheld.  To 

eliminate the possibility of interference from instruments or 

alternator we tested with the master off and the problem still exists.

  Then it's not electrical noise. Sounds more like acoustic

  noise coming in through the microphone(s).

    	  Quote: 	
		  >Previously the A24 was used acceptably with an open cockpit biplane, 

 	  Quote: 	
		  a Murphy Renegade.

One possibility could be excessive gain using the external mike, but 

I am skeptical since it was acceptable in the biplane

Any suggestions?

  You need to identify the nature of the noise. Props sound

  different that exhausts which sound different than

  ignition, strobes, EL panel inverters, etc.

  If you key the hand-held with the external headset

  disconnected and a tape over the built in microphone,

  is it quiet then?

  Bob . . .

[b]

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nuckolls.bob(at)aeroelect
Guest

Posted: Mon Mar 08, 2010 7:13 am Post subject: Noise in Handheld Tx signal

At 07:21 AM 3/8/2010, Lapsley R. and Sandra E. Caldwell wrote:



  	  Quote: 	
		   	  Quote: 	
		  As is frequently the case,

once you truly identify the root cause of a problem the solution is

obvious.



In this case we were using an external headset with the A24 hand held

without an external PTT.  In other words we were using the hand held

Tx button for the PTT.  The owners manual did not say if the

external PTT was either recommend or necessary with an external headset.



After discussing the problem with ICOM tech support they told me that

when you press the hand held TX button it connects the internal mic as

well as the external mic to the transmitted carrier.  Consequently

when we tried to transmit without the engine running the Tx signal was

reasonably quite but with the engine running the mic in the hand held

picked up the cockpit noise and transmitted it along with the voice from

the headset mic.



Correction of this problem was easy we just used an external PTT. 

Just one more wire in the cockpit



I suspect that this may be common to other handhelds.

	
	


   Great datapoint! Thanks for sharing.



   Bob . . .

     [quote][b]

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