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vhf transponder interference

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jappie

Joined: 28 Oct 2012
Posts: 11
Location: Montreal

Posted: Mon Oct 29, 2012 1:40 pm Post subject: vhf transponder interference

Hello everyone



I'm a new member here and looking for some help on a problem I've noticed approx. 2 years ago.



1- When I transmit on my Garmin GNC 250XL, some gauges on my panel go haywire. ie: Mitchell fuel level indicator.



2- When I trasnmit, ATC tells me my altitude changes on his radar ( transponder Garmin GTX-320) encoder AK-350.



3- When I put my X-Ponder from Off to any position ( SBY, ON, ALT ) a "White" noise can be heard in my headset ( only while receiving).



4-Receiving deteriorate as the flight goes.



airplane all fiberglass, C-GGYY to see pictures



Thank you



Jean-Pierre

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Oct 30, 2012 5:19 am Post subject: vhf transponder interference

At 04:40 PM 10/29/2012, you wrote:

 	  Quote: 	
		  



Hello everyone



I'm a new member here and looking for some help on a problem I've 

noticed approx. 2 years ago.



1- When I transmit on my Garmin GNC 250XL, some gauges on my panel 

go haywire. ie: Mitchell fuel level indicator.



2- When I trasnmit, ATC tells me my altitude changes on his radar ( 

transponder Garmin GTX-320) encoder AK-350.



3- When I put my X-Ponder from Off to any position ( SBY, ON, ALT ) 

a "White" noise can be heard in my headset ( only while receiving).



4-Receiving deteriorate as the flight goes.



airplane all fiberglass, C-GGYY to see pictures


	


    Your cockpit is "hot" with RF energy generated

    by the transmitter. The most prevalent cause of

    this condition is a poorly installed coax connector

    at either end of the comm antenna feeder but

    especially the transceiver end.



    Check this connector to make sure the shield

    ground integrity is good.



   Bob . . .

jappie

Joined: 28 Oct 2012
Posts: 11
Location: Montreal

Posted: Wed Oct 31, 2012 1:52 pm Post subject: Re: vhf transponder interference

thank you Bob



I've also found on "Google" that I should have a Notch filter installed, as per Garmin,  which I don't have....



I bought the plane 9 years ago as is....



I will check the coax cable during winter maintenance.



JP

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Nov 01, 2012 5:57 am Post subject: vhf transponder interference

At 04:52 PM 10/31/2012, you wrote:

 	  Quote: 	
		  



thank you Bob



I've also found on "Google" that I should have a Notch filter 

installed, as per Garmin,  which I don't have....



I bought the plane 9 years ago as is....



I will check the coax cable during winter maintenance.



JP




	


   Can you point me to the website that recommends/offers

   this 'notch filter'?



   Bob . . .

jappie

Joined: 28 Oct 2012
Posts: 11
Location: Montreal

Posted: Thu Nov 01, 2012 12:18 pm Post subject: Re: vhf transponder interference

This is a .pdf  file:  installation manual for Garmin 250 XL



page 9 & 10 Notch filter required, but I understand that it if for GPS interference, not my problem, but still say I need it anyway.



JP



http://trackeraff.com/IAS/manuals/Garmin/GNC%20250/156_InstallationManual.pdf

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Nov 01, 2012 1:26 pm Post subject: vhf transponder interference

At 03:18 PM 11/1/2012, you wrote:

 	  Quote: 	
		  



This is a .pdf  file:  installation manual for Garmin 250 XL



page 9 & 10 Notch filter required, but I understand that it if for 

GPS interference, not my problem, but still say I need it anyway.



JP


	


   Okay. The GPS signal radiated by satellites is VERY

   small. At the same time, your VHF transmitter is designed

   to transmit most strongly in the 118 to 135 range, a range

   that brackets 131.285.  The 12th harmonic of this frequency

   falls on the GPS center frequency of 1.57542 Ghz.



   A check you can make first is to see how transmissions

   on frequence adjacent to the 'rosewood stake' affects

   GPS performance. Watch GPS signal strengths while keying

   the transmitter on say on all the notches between 131.2

   and 131.35. See if the signal strengths degrade to causing

   the GPS to loose track.



   If so, try the VHF comm frequencies down to day 131 and up

   to 132 . . . how close CAN you be to the rosewood stake and

   not affect the GPS.



   Then count how many times you've used frequencies in that

   range and further, asses the risk to comfortable conduct

   of the flight if you DO happen to whack the GPS signal

   on occasion.



   I've flown a lot of GPS aided miles and never noticed

   a loss of nav data event. Even if it had occurred, I might

   not have noticed it. I think it's a good thing to be

   aware of . . . and watch for . . . but not sure it's worth

   the price of this notch filter. That assumes that it costs

   more than $0.50 and the top off a box of Wheaties.



   If you find that you don't have noteworthy interference,

   let us know what you find. I've been aware of the potential

   for this issue but I can't recall it rising up in conversations

   at HBC.  Wayyyyy back when, we had some problems with

   signals radiated from the RECEIVER oscillators interfering

   with GPS. That required fabrication of a shield screen to

   stack between the two radios.



   Bob . . .

jappie

Joined: 28 Oct 2012
Posts: 11
Location: Montreal

Posted: Sun Nov 04, 2012 12:49 pm Post subject: Re: vhf transponder interference

Hello



Just got back from the hangar, did some test with my VHF radio, (outside)

Looked at the Satellite  strength signal, my average was 7.8,

TX on freq. 131.20 up to 131.35 and did see a decrease in strength signal averaging 3.7, at one point, I got the poor coverage warning.



So, next step, inspect my connectors, coax, antenna, ground plate...etc. Winter project.

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Nov 04, 2012 4:12 pm Post subject: vhf transponder interference

At 02:49 PM 11/4/2012, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "jappie" <jappie(at)videotron.ca>



 Hello



 Just got back from the hangar, did some test with my VHF radio, (outside)

 Looked at the Satellite  strength signal, my average was 7.8,

 TX on freq. 131.20 up to 131.35 and did see a decrease in strength signal averaging 3.7, at one point, I got the poor coverage warning.



 So, next step, inspect my connectors, coax, antenna, ground plate...etc. Winter project. 	


    Not sure there's anything 'wrong' with your as-installed

    transceiver. The VHF comm transmitter WILL have harmonic

    content in its output. It's an expected condition that's

    tested during the TSO qualification process.



    You're probably seeing a manifestation of a special

    case were the transmitter might be very good in the

    world of terrestrial communications and navigation

    but offers insult to the very tiny GPS satellite

    signals . . . but only in a narrow range of circumstances

    and intermittently at that.



    I think you're golden. Adding the suggested 'notch filter'

    in your transceiver's antenna feeder will no doubt

    improve on your observed interference in the range of

    interest so if you don't mind the expense off adding the

    filter . . .it's not a big thing



   



   Aircraft Spruce has the one above for about $110.



   Found this one on eBay for $25 plus too much shipping (by it

   now).



  http://tinyurl.com/c3e68jf



   You could make a best offer of say $25 if he

   ships it first class in a padded envelope for $2.00.



   I went to the workbench and fiddled with a 'po man's

   notch filter.



 [img]cid:.0[/img]



 

   While you're hammering on the airplane this winter, you might

   conduct the experiment above. Let us know what your final dimension

   is. Yes, the 'active dimension' includes conductors inside the

   coax T-connector. You'll want to do some look-see at the 13th

   harmonics too . . . near and either side of 121.25 Mhz. In fact,

   do the initial experiments at the 13th harmonic values . . . odd

   harmonics from transmitters tend to be much stronger than

   even ones.



   I see that Comant is now offering VHF antennas with GPS notch

   filtering built in. Cool move.



   Here's a thread on VansAF forum where a builder was experiencing

   severe interference 



  http://tinyurl.com/a3em5l2



 



   



 



 

   Bob . . .

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jappie

Joined: 28 Oct 2012
Posts: 11
Location: Montreal

Posted: Wed Jan 16, 2013 5:56 pm Post subject: Re: vhf transponder interference

hello



Went to my hangar last week, started to remove radio equipment. Took the coax cable and brought it to work to show to the "experts", Electronic Dept.



One  BNC connector is a twist (screw-in) type, I find that cheap to use on aircraft (personal opinion). Anyway, we started un-twisting the connector and wow, no crimp with the middle pin, is that normal ? and shield was almost gone !! see picture.

Coax is (was) RG58C/U and will be replaced by RG142.

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Jan 17, 2013 7:52 am Post subject: vhf transponder interference

At 07:56 PM 1/16/2013, you wrote:

 	  Quote: 	
		  



hello



Went to my hangar last week, started to remove radio equipment. Took 

the coax cable and brought it to work to show to the "experts", 

Electronic Dept.



One  BNC connector is a twist (screw-in) type, I find that cheap to 

use on aircraft (personal opinion). Anyway, we started un-twisting 

the connector and wow, no crimp with the middle pin, is that normal 

? and shield was almost gone !! see picture.

Coax is (was) RG58C/U and will be replaced by RG142.


	


   It was time to replace that connector before it

   flew for the first time!



   Bob . . .

jappie

Joined: 28 Oct 2012
Posts: 11
Location: Montreal

Posted: Fri Jan 18, 2013 9:26 am Post subject: Re: vhf transponder interference

ha !



I've just learned that Twist Type BNC connectors should be use with solid center conductor only....



JP

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Jan 18, 2013 9:56 am Post subject: vhf transponder interference

At 11:26 AM 1/18/2013, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "jappie" <jappie(at)videotron.ca>



 ha !



 I've just learned that Twist Type BNC connectors should be use with solid center conductor only.... 	


   I would argue further that twist on connectors should

   not be used for any connector.  Well, with one exception.

   Those 'wire nuts' favored by electrical contractors for

   the wiring of buildings are very interesting examples

   for the achievement of high-pressure, gas-tight contact

   with wires using low force, solderless techniques.

 [img]cid:.0[/img]



   This type of twist-on connector brings a number of circular

   cross-sections into contact with each other. Two circles

   contact each other with zero-area . . . i.e. relatively

   small forces can produce very high pressures that will

   offer good electrical connection as long as there are no

   extra-ordinary environmental effects. This is why

   wire-nuts are not recommended for any vehicular application.



   Twist-on connectors for coax attempt to develop long

   lasting, high pressure connection to copper strands being

   backed up by PLASTIC. Further, environmental

   stresses on the made up joint are much more severe

   than the protected confines of your house's breaker

   and switch boxes.



   Contrary to the inventor's fondest wishes, the twist-on

   coax connector was designed to fail.



 

   Bob . . .

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jappie

Joined: 28 Oct 2012
Posts: 11
Location: Montreal

Posted: Tue Mar 05, 2013 6:07 pm Post subject: Re: vhf transponder interference

Here is my new RG-142 cable.



pictures are in the wrong order 



JP

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jappie

Joined: 28 Oct 2012
Posts: 11
Location: Montreal

Posted: Fri Mar 15, 2013 4:18 pm Post subject: Re: vhf transponder interference

Hello again



After making a new comm cable , I decided to replace the x-ponder cable also, GTX-320, so I removed the old one and found my BNC connector (coax panel mount)  to be a TED 9-30-11 ( look at the picture) but can't find anything on 9-30-11, instead everything I find is 9-30-10.... 



JP

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Bob McC

Joined: 09 Jan 2006
Posts: 258
Location: Toronto, ON

Posted: Fri Mar 15, 2013 6:18 pm Post subject: vhf transponder interference

Just did a Google search for "ted 9-30-11". 



Very first hit was this link: 	http://tinyurl.com/aatlnmk



12th item down the list was this item: 	http://tinyurl.com/au3o3q7



Appears to be the part you're asking for, not the -10 alternate which is the

6th item down the same list.	http://tinyurl.com/a7yyv3z	



Bob McC

[quote] --

_________________
Bob McC
Falco #908
(just starting)

jappie

Joined: 28 Oct 2012
Posts: 11
Location: Montreal

Posted: Sat Mar 16, 2013 5:25 am Post subject: Re: vhf transponder interference

[quote="Bob McC"]Just did a Google search for "ted 9-30-11". 



Very first hit was this link: 	http://tinyurl.com/aatlnmk



12th item down the list was this item: 	http://tinyurl.com/au3o3q7



Appears to be the part you're asking for, not the -10 alternate which is the

6th item down the same list.	http://tinyurl.com/a7yyv3z	



Bob McC

 	  Quote: 	
		   -- 	


yup. that is the only site I found too ( I lied !!). wonder what is the difference between them. (-10  -11)



Could I replace it by DBA-600   ???



JP

jappie

Joined: 28 Oct 2012
Posts: 11
Location: Montreal

Posted: Wed Mar 20, 2013 7:34 am Post subject: Re: vhf transponder interference

what is the importance of the Impedance bushing inside this connector TED 9-30-10 ?



I've been told to use use it only with a certain type of cable ...



My old one had none, maybe one of the many reasons I have interference...



JP

nuckolls.bob(at)aeroelect
Guest

Posted: Thu Mar 21, 2013 9:07 am Post subject: vhf transponder interference

At 10:34 AM 3/20/2013, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "jappie" <jappie(at)videotron.ca>



 what is the importance of the Impedance bushing inside this connector TED 9-30-10 ?



 I've been told to use use it only with a certain type of cable ..



 My old one had none, maybe one of the many reasons I have interference...



 JP

 	


  I wrote to TED Mfg to ask for their published instructions

  on assembly of this connector.  An excerpt from their reply

  is shown below:



 [img]cid:7.1.0.9.0.20130321120308.048a19f0(at)aeroelectric.com.0[/img] 



   I'll publish the entire document in the Manufacturer's data

   folder of aeroelectric.com later today.



   The bushing you asked about is used for smaller coaxes.

   The .2" diameter coaxes like 58, 400, 142, etc do not

   require it.



 

   Bob . . .

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jappie

Joined: 28 Oct 2012
Posts: 11
Location: Montreal

Posted: Wed Mar 27, 2013 12:03 pm Post subject: Re: vhf transponder interference

Thank you Bob



I did my soldering last weekend with RG-142 but I installed the impedance bushing not knowing better, anyhow, I don't think it will be harmfull.



JP

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