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Transponder noise

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dustinp(at)hughes.net
Guest

Posted: Wed Mar 07, 2007 5:40 am Post subject: Transponder noise

After installing my radio stack (GNS 430, SL-40, GTX 330, GMA 340) and 

firing it up for the first time, I find that I can hear the ticking 

transponder broadcast signal in my headset (as well as on a AM/FM radio that 

was turned on in the shop at the time).

I thought my com antennae may be to close to my transponder antenna, but I 

can still hear the ticking broadcast even when the com radios are turned 

off, and only the audio panel is left on. The ticking stops when the 

transponder is placed in standby mode or turned off, so I know that is where 

it is coming from.

Thanks for any ideas on how this can be cured?

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nuckollsr(at)cox.net
Guest

Posted: Wed Mar 07, 2007 10:30 am Post subject: Transponder noise

At 07:39 AM 3/7/2007 -0600, you wrote:



 	  Quote: 	
		  



After installing my radio stack (GNS 430, SL-40, GTX 330, GMA 340) and 

firing it up for the first time, I find that I can hear the ticking 

transponder broadcast signal in my headset (as well as on a AM/FM radio 

that was turned on in the shop at the time).

I thought my com antennae may be to close to my transponder antenna, but I 

can still hear the ticking broadcast even when the com radios are turned 

off, and only the audio panel is left on. The ticking stops when the 

transponder is placed in standby mode or turned off, so I know that is 

where it is coming from.


	


 	  Quote: 	
		  Thanks for any ideas on how this can be cured?


	


  While your antagonist and victim have been identified, you

  still need to identify the propagation mode. When presented

  with your situation, we know that there is a combination

  of three things that may eliminate the noise problem or at

  least reduce it to unnoticeable levels.



  (1) Fix some issue with the antagonist that doesn't

      conform to industry practice for integrating

      the product into an aircraft.



  (2) Fix some issue with the victim that doesn't

      conform to industry practice for integrating

      the product into an aircraft.



  (3) Eliminate or attenuate the propagation mode that

      brings energy from the antagonist to vulnerable

      components of the victim.



  When anyone hears a short burst of "buzz" synchronous

  with illumination of the transponder REPLY light, 90%

  of the time it's an RF detection of the reply pulses

  someplace in the audio stream. Obviously, our best

  starting assumption is to set actions (1) and (2)

  aside. Most of the time, the hardware we install has

  been competently designed and tested to live in the

  aircraft environment. So let's talk about (3).



  What kind of audio panel? What are the connectors

  on the back like? Is your airplane composite or

  metal? Where is the transponder antenna mounted with

  respect to the panel?



  Bob . . .

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Dustin Paulson

Joined: 11 Jan 2006
Posts: 1
Location: Mora, MN

Posted: Thu Mar 08, 2007 5:33 am Post subject: Re: Transponder noise

What kind of audio panel? What are the connectors

  on the back like? Is your airplane composite or

  metal? Where is the transponder antenna mounted with

  respect to the panel?



  Bob . . . 



Bob,



The audio panel is Garmin GMA 340 with 2 large D-sub connetors on the back. I had Approach Systems build the harness for it, as well as all the other avionics, and use their avionics hub to connect everything together.

 

The plane is a highwing GlaStar, which has chrome molly passenger cage surrounded by a fiberglass fuselage, and vertical stabilizer. It has aluminum wings, rudder, and horizontal stabilizer.

I built a composite battery shelf that spans the fuselage sides behind the bulkhead that seperates the baggage compartment from the empanage. In addition to the battery on one end, the ELT is located on the other end, and the transponder antenna inbetween, with the ground plane mounted on top of the shelf, and the element hanging underneath. This places the antenna about 8 feet behind the panel.



I thought the foil tape marker beacon antenna glassed to the belly of the empanage may be picking up the transponder broadcast since it is hooked directly to the audio panel. So this morning I went out and diconnected the marker beacon coax from its lead on the audio panel harness, while I listened to my headset. However there was no change in the ticking when I diconnected the coax. 

I did notice a significant change in the volume of the ticking when my physical position changed as I moved around the plane to make the disconnection. I also noted that when I turned off the ANR on my LightSpeed headset, the ticking was no longer audible, but I really don't want to fly without the ANR since it makes radio transmissions so much easier to hear.

It does seem like there is something in the headset or ANR circuitry that is picking up the transponder transmission. Has anyone else experienced this? and if so did you find a fix??



Thanks

Dustin Paulson

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nuckollsr(at)cox.net
Guest

Posted: Fri Mar 09, 2007 5:55 am Post subject: Transponder noise

At 05:33 AM 3/8/2007 -0800, you wrote:



 	  Quote: 	
		  

<dustinp(at)direcway.com>



What kind of audio panel? What are the connectors

   on the back like? Is your airplane composite or

   metal? Where is the transponder antenna mounted with

   respect to the panel?



   Bob . . .



Bob,



The audio panel is Garmin GMA 340 with 2 large D-sub connetors on the 

back. I had Approach Systems build the harness for it, as well as all the 

other avionics, and use their avionics hub to connect everything together.



The plane is a highwing GlaStar, which has chrome molly passenger cage 

surrounded by a fiberglass fuselage, and vertical stabilizer. It has 

aluminum wings, rudder, and horizontal stabilizer.

I built a composite battery shelf that spans the fuselage sides behind the 

bulkhead that seperates the baggage compartment from the empanage. In 

addition to the battery on one end, the ELT is located on the other end, 

and the transponder antenna inbetween, with the ground plane mounted on 

top of the shelf, and the element hanging underneath. This places the 

antenna about 8 feet behind the panel.


	


    But it also places the panel and all stuff in the cockpit right in the

    antenna's major radiation pattern. I've never been too happy with the

    notion of internal transponder antennas. Sticking them out the bottom

    of the fuselage offers an opportunity to reduce radiation to the

    ship's other systems by a factor of 100 or more.

 	  Quote: 	
		  I thought the foil tape marker beacon antenna glassed to the belly of the 

empanage may be picking up the transponder broadcast since it is hooked 

directly to the audio panel. So this morning I went out and diconnected 

the marker beacon coax from its lead on the audio panel harness, while I 

listened to my headset. However there was no change in the ticking when I 

diconnected the coax.

I did notice a significant change in the volume of the ticking when my 

physical position changed as I moved around the plane to make the 

disconnection.


	


    Yup. Your antenna location is filling the cockpit with

    RF stresses . . . moving around within the cockpit will

    "stir" the pattern of maximum stress.



 	  Quote: 	
		    I also noted that when I turned off the ANR on my LightSpeed headset, 

 the ticking was no longer audible, but I really don't want to fly without 

 the ANR since it makes radio transmissions so much easier to hear.

It does seem like there is something in the headset or ANR circuitry that 

is picking up the transponder transmission. Has anyone else experienced 

this? and if so did you find a fix??


	


   Is the ANR headset specifically for aircraft? It

   may or may not be designed to live in the aircraft

   radio noise environment. In any case, try moving the

   antenna to the belly and put either a tuned (radius

   equal to antenna mounted height) or a would-like-

   to-be-infinite (as generous as practical) ground

   plane over the antenna's mounting location. In this

   case, an 'oversized' ground plane goes to the task

   of minimizing radiation in the direction of the cabin.



   Bob . . .

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