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Transponder antenna location

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rv(at)thelefflers.com
Guest

Posted: Mon Aug 10, 2009 1:40 pm Post subject: Transponder antenna location

I’m in the process of installing doublers for all of my antennas attached to the fuselage bottom.  

   

I understand that the transponder antenna coax run should be 3’to 8.8’.   I know that some have mounted the transponder antenna in the center tunnel near the firewall.  Others appear to have located it under the rear seat or baggage area.   Since this appears to require a coax run of longer than 8.8’, I’m curious to what issues (or lack thereof) folks have experienced when they located their transponder antennas in these areas?  Is 8.8’ really a hard limited from Garmin?  

   

Thanks,  

   

Bob  

#40684  

      [quote][b]

scottmschmidt(at)yahoo.co
Guest

Posted: Mon Aug 10, 2009 3:23 pm Post subject: Transponder antenna location

I never knew of the 8' rule.  I did read that 48" (I think, may be more) from any COM antenna was very important which is why I put it aft of the baggage compartment and have not had any issues. 

 

Scott Schmidtscottmschmidt(at)yahoo.com



From: Bob Leffler <rv(at)thelefflers.com>

To: rv10-list(at)matronics.com

Sent: Monday, August 10, 2009 3:42:44 PM

Subject: Transponder antenna location



                

Iâ€™m in the process of installing doublers for all of my antennas attached to the fuselage bottom.   

     

I understand that the transponder antenna coax run should be 3â€™to 8.8â€™.   I know that some have mounted the transponder antenna in the center tunnel near the firewall.  Others appear to have located it under the rear seat or baggage area.   Since this appears to require a coax run of longer than 8.8â€™, Iâ€™m curious to what issues (or lack thereof) folks have experienced when they located their transponder antennas in these areas?  Is 8.8â€™ really a hard limited from Garmin?   

     

Thanks,   

     

Bob   

#40684   

      [quote]http://www.matronics.com/Navigator?RV10-List<//www.matronics.com/contribution">http://www.matronics.com/contribution============


[b]

tc1234c(at)roadrunner.com
Guest

Posted: Mon Aug 10, 2009 5:11 pm Post subject: Transponder antenna location

Bob,

 

 I don't see the minimum coaxial cable length in the installation manual (Garmin 327). The maximum 8.8' is for RG 400. On my 9A I have the TED antenna mounted right besides right gear mount and worked well. I keep it three feet away from my main COM antenna. There is no interference at all. On my 10 I will try to run all my antenna cables as short as possible.

  

  

  	  Quote: 	
		  Ted Chang

RV9A flying, RV10 Wing

http://3limafoxtrot.com

my flight track:

http://www.mail2600.com/cgi-bin/track.cgi?call=KD8IIR&last=1

	
 

 On 8/10/2009 5:42 PM, Bob Leffler wrote: [quote]                 <![endif]-->       <![endif]-->      

I’m in the process of installing doublers for all of my antennas attached to the fuselage bottom.   

    

I understand that the transponder antenna coax run should be 3’to 8.8’.   I know that some have mounted the transponder antenna in the center tunnel near the firewall.  Others appear to have located it under the rear seat or baggage area.   Since this appears to require a coax run of longer than 8.8’, I’m curious to what issues (or lack thereof) folks have experienced when they located their transponder antennas in these areas?  Is 8.8’ really a hard limited from Garmin?   

    

Thanks,   

    

Bob   

#40684   

    	  Quote: 	
		  



 href="http://www.matronics.com/Navigator?RV10-List">http://www.matronics.com/Navigator?RV10-List

 href="http://forums.matronics.com">http://forums.matronics.com

 href="http://www.matronics.com/contribution">http://www.matronics.com/contribution



	
 [b]

AirMike

Joined: 27 Feb 2007
Posts: 514
Location: Nevada

Posted: Mon Aug 10, 2009 9:57 pm Post subject: Transponder antenna location

In Tunnel - under seat - watch out for glowing genitals

I can't help it. I am a sick man.



Seriously though, the radiation issue was discussed some time ago on this list. Not an issue

_________________
See you OSH '18
Q/B - sold.

Ron.McGann(at)thalesgroup
Guest

Posted: Mon Aug 10, 2009 10:48 pm Post subject: Transponder antenna location

8.8' of RG400, 12.5' of RG304, 17' of RG393.



Some may know that I've had the 'leans' with my GRT EFIS.  Initialises

perfectly on the ground with no anomalous heading, but tilts 3-4deg once

airborne.  I have my XPDR antenna in the tunnel beneath the fwd baggage

area, with the magnetometer in the 'stock' location on a shelf above and

aft of the battery.  Since the XPDR only transmits once airborne ('SBY'

on the ground and automatically enters 'ALT' mode), and the AHRS only

leans in flight, me thinks that perhaps the XPDR antenna is too close to

the magnetometer and may be interfering when responding to a ping . . .

tc1234c(at)roadrunner.com
Guest

Posted: Tue Aug 11, 2009 12:54 am Post subject: Transponder antenna location

Ron,



Contact GRT for your lean problem. I don't think it is due to RF 

interference. I had that problem 520 hrs ago (at 120 hr). Called GRT and 

sent in a log file. They confirmed it was a bad MEMS gyro. They replaced 

both my magnetometer and AHRS (must be in pairs).  I have no lean 

problem ever since.



Ted



Ted Chang

RV9A flying, RV10 Wing

http://3limafoxtrot.com

my flight track:

http://www.mail2600.com/cgi-bin/track.cgi?call=KD8IIR&last=1

On 8/11/2009 2:46 AM, McGann, Ron wrote:

[quote] 



 8.8' of RG400, 12.5' of RG304, 17' of RG393.



 Some may know that I've had the 'leans' with my GRT EFIS.  Initialises

 perfectly on the ground with no anomalous heading, but tilts 3-4deg once

 airborne.  I have my XPDR antenna in the tunnel beneath the fwd baggage

 area, with the magnetometer in the 'stock' location on a shelf above and

 aft of the battery.  Since the XPDR only transmits once airborne ('SBY'

 on the ground and automatically enters 'ALT' mode), and the AHRS only

 leans in flight, me thinks that perhaps the XPDR antenna is too close to

 the magnetometer and may be interfering when responding to a ping . . .

 .



 Will turn the XPDR off next flight and see what happens.



 Cheers,

 Ron

 VH-XRM flying in Oz



 --

wayne.e(at)grandecom.net
Guest

Posted: Tue Aug 11, 2009 3:57 am Post subject: Transponder antenna location

Hi Bob,

  

 I installed mine in the tunnel forward to the  firewall. It made the run very easy and I've had no difficulties that I'm aware  of.

  

 Wayne Edgerton

 N602WT 

  

  

             Time:      02:40:21 PM PST    US            From:      "Bob Leffler" <rv(at)thelefflers.com (rv(at)thelefflers.com)>            Subject:      Transponder antenna        location       

      I'm in the process of installing doublers for  all of my antennas attached to

      the fuselage  bottom.

      

       

      I understand that the transponder antenna  coax run should be 3'to 8.8'.   I

       know that some have mounted the transponder antenna in the center  tunnel

      near the firewall.  Others appear  to have located it under the rear seat or

       baggage area.   Since this appears to require a coax run of longer  than

      8.8', I'm curious to what issues (or lack  thereof) folks have experienced

      when they  located their transponder antennas in these areas?  Is 8.8'  really

      a hard limited from  Garmin?

      

       

      Thanks,

       

      

       Bob

      

       #40684



    [quote][b]

Tim Olson

Joined: 25 Jan 2007
Posts: 2872

Posted: Tue Aug 11, 2009 7:14 am Post subject: Transponder antenna location

I don't know that it would be a XPDR antenna location issue

that would cause your leans, but, the XPDR antenna does

put out something pretty strong...I think I heard 75W

or so?  So it's probably a good idea to keep it at least

a couple feet from the AHRS/Magnetometer.



Tim Olson - RV-10 N104CD

do not archive

McGann, Ron wrote:

[quote] 

 

 8.8' of RG400, 12.5' of RG304, 17' of RG393.

 

 Some may know that I've had the 'leans' with my GRT EFIS.  Initialises

 perfectly on the ground with no anomalous heading, but tilts 3-4deg once

 airborne.  I have my XPDR antenna in the tunnel beneath the fwd baggage

 area, with the magnetometer in the 'stock' location on a shelf above and

 aft of the battery.  Since the XPDR only transmits once airborne ('SBY'

 on the ground and automatically enters 'ALT' mode), and the AHRS only

 leans in flight, me thinks that perhaps the XPDR antenna is too close to

 the magnetometer and may be interfering when responding to a ping . . .

 .

 

 Will turn the XPDR off next flight and see what happens. 

 

 Cheers,

 Ron

 VH-XRM flying in Oz

 

 --

Phil.Perry(at)netapp.com
Guest

Posted: Tue Aug 11, 2009 7:20 am Post subject: Transponder antenna location

That makes a lot of sense on the limitation.  I’ll bet 8.8’ is a multiple of the wavelength where they begin to lose significant amounts of their effective radiated power  (erp).  

   

At the 1Ghz frequency range, the amount of signal loss is very high.  The wavelengths are tremendously short and it takes a lot to get the signal out the other end of the coax and still have enough energy remaining at the antenna to broadcast a signal.  

   

The rule of thumb for all coax runs is to keep them as short as possible and to use higher-end coax on the higher frequencies.    

   

It’s usually not that big of a deal at the VHF frequencies, but you still want to keep them fairly short because VHF is still pretty lossy – But it’s nothing like the Ghz frequency range.  I’ve measured power at the end of a 10’ coax run in the 1.2ghz area and that’s when it really sunk in at how much was lost in the coax.   

   

The shorter the better and the lower loss the coax the better.  

   

Phil  

   

   

   

   

   

       

From: Bob Leffler [mailto:rv(at)thelefflers.com] 

 Sent: Monday, August 10, 2009 4:43 PM

 To: rv10-list(at)matronics.com

 Subject: Transponder antenna location  

  

  

   

I’m in the process of installing doublers for all of my antennas attached to the fuselage bottom.  

   

I understand that the transponder antenna coax run should be 3’to 8.8’.   I know that some have mounted the transponder antenna in the center tunnel near the firewall.  Others appear to have located it under the rear seat or baggage area.   Since this appears to require a coax run of longer than 8.8’, I’m curious to what issues (or lack thereof) folks have experienced when they located their transponder antennas in these areas?  Is 8.8’ really a hard limited from Garmin?  

   

Thanks,  

   

Bob  

#40684   	  Quote: 	
		    http://www.matronics.com/Navigator?RV10-List 	
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      [quote][b]

bcondrey

Joined: 03 Apr 2006
Posts: 580

Posted: Tue Aug 11, 2009 7:21 am Post subject: Transponder antenna location

It's actually 250 watts (for a GTX-330).  The aluminum airframe is

likely shielding the signal from the AHRS in question and it's unlikely

that it would be causing the issue.  



I've got my antenna below the bay where the battery is and haven't had

any issues (transponder or otherwise).



Bob

N442PM



--

Lenny Iszak

Joined: 23 Mar 2008
Posts: 270

Posted: Tue Aug 11, 2009 9:12 am Post subject: Re: Transponder antenna location

Also the transponder is transmitting in very short bursts, so you'd probably see those bursts showing up on your magnetometer if this was the issue.

But as Bob said, the airframe is shielding that signal from reaching the magnetometer, just as it shields your genitals...  Yeah, just come to think of it, I put my transponder antenna under the pilot seat... ooops.



Lenny

Bob Turner

Joined: 03 Jan 2009
Posts: 885
Location: Castro Valley, CA

Posted: Tue Aug 11, 2009 9:20 am Post subject: Re: Transponder antenna location

Nine feet of RG-400 loses about 30% of the power at 1 GHz. leaving you with 70% of what you started with (not counting connector losses). So if you double the length, to 18 feet, you only get 49% of what you started with to the antenna.

This sounds like a lot (and it is!) but in practice if the shorter length works okay when you're 100 nm from the radar antenna, then the 18 feet will work okay when you're within 84 miles (square root of 0.7) of the antenna site. Not really that much difference.

For years I've flown a 182 with the transponder antenna in the back, more than 9 feet of coax. Always works okay,passes biennial tests. So try to keep lengths down, but don't worry too much. Do make sure you use good connectors.

_________________
Bob Turner
RV-10 QB

Kelly McMullen

Joined: 16 Apr 2008
Posts: 1188
Location: Sun Lakes AZ

Posted: Tue Aug 11, 2009 9:42 am Post subject: Transponder antenna location

You will find most factory built aircraft will have the transponder and DME antennas right below the front seat ankle area or just ahead of leading edge of wing on belly. Why give away power and pay more for cable?



 On Tue, Aug 11, 2009 at 10:20 AM, Bob Turner <bobturner(at)alum.rpi.edu (bobturner(at)alum.rpi.edu)> wrote:

[quote] --> RV10-List message posted by: "Bob Turner" <bobturner(at)alum.rpi.edu (bobturner(at)alum.rpi.edu)>

 

 Nine feet of RG-400 loses about 30% of the power at 1 GHz. leaving you with 70% of what you started with (not counting connector losses). So if you double the length, to 18 feet, you only get 49% of what you started with to the antenna.

  This sounds like a lot (and it is!) but in practice if the shorter length works okay when you're 100 nm from the radar antenna, then the 18 feet will work okay when you're within 84 miles (square root of 0.7) of the antenna site. Not really that much difference.

  For years I've flown a 182 with the transponder antenna in the back, more than 9 feet of coax. Always works okay,passes biennial tests. So try to keep lengths down, but don't worry too much. Do make sure you use good connectors.

  

 --------

 Bob Turner

 RV-10 QB

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=257160#257160

 

 

 

 

 

 

 

 ===========

 arget="_blank">http://www.matronics.com/Navigator?RV10-List

 ===========

 http://forums.matronics.com

 ===========

 le, List Admin.

 ="_blank">http://www.matronics.com/contribution

 ===========

 

 

 

 [b]

_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor
KCHD

Bob Turner

Joined: 03 Jan 2009
Posts: 885
Location: Castro Valley, CA

Posted: Tue Aug 11, 2009 1:15 pm Post subject: Re: Transponder antenna location

Maybe I'm wrong; my observation is most factory planes try to separate the DME and transponder antennas by as much as they can, since they operate on frequencies that are nearly the same. That's how you end up with long cable runs to the transponder. I think most DMEs can even be connected to the transponder, so they know not to 'listen' when the transponder transmits.



But overall I agree, it's best to minimize the coax runs, especially at a GHz.



Has anyone with a forward mounted antenna had any heat issues, similar to the hot tunnel issues?

_________________
Bob Turner
RV-10 QB

Kelly McMullen

Joined: 16 Apr 2008
Posts: 1188
Location: Sun Lakes AZ

Posted: Tue Aug 11, 2009 1:37 pm Post subject: Transponder antenna location

If you look at a few single Cessnas you will find DME and transponder on opposite sides of the fuselage with maybe 36-40" separation. I'm sure that is more than a couple wavelengths, and yes I believe there is an interconnect cable to keep their pulse transmissions separated.

 

On Tue, Aug 11, 2009 at 2:15 PM, Bob Turner <bobturner(at)alum.rpi.edu (bobturner(at)alum.rpi.edu)> wrote:

[quote] --> RV10-List message posted by: "Bob Turner" <bobturner(at)alum.rpi.edu (bobturner(at)alum.rpi.edu)>

 

 Maybe I'm wrong; my observation is most factory planes try to separate the DME and transponder antennas by as much as they can, since they operate on frequencies that are nearly the same. That's how you end up with long cable runs to the transponder. I think most DMEs can even be connected to the transponder, so they know not to 'listen' when the transponder transmits.

  

 But overall I agree, it's best to minimize the coax runs, especially at a GHz.

 

 Has anyone with a forward mounted antenna had any heat issues, similar to the hot tunnel issues?

 

 --------

 Bob Turner

 RV-10 QB

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=257184#257184

 

 

 

 

 

 

 

 ===========

 arget="_blank">http://www.matronics.com/Navigator?RV10-List

 ===========

 http://forums.matronics.com

 ===========

 le, List Admin.

 ="_blank">http://www.matronics.com/contribution

 ===========

 

 

 

 [b]

_________________
Kelly McMullen
A&P/IA, EAA Tech Counselor
KCHD

rv10free2fly(at)yahoo.com
Guest

Posted: Tue Aug 11, 2009 5:12 pm Post subject: Transponder antenna location

Wayne, could you please indicate the distance back from the firewall for the trasnponder antenna please?

  

 Any effect on the antenna as a resut of the exhaust?

  

 Regards

  

 Patrick Pulis

 #40299

 South Oz 



 

   From: Wayne Edgerton <wayne.e(at)grandecom.net>

To: rv10-list(at)matronics.com

Sent: Tuesday, 11 August, 2009 9:25:57 PM

Subject: Re: Transponder antenna location



   Hi Bob,

  

 I installed mine in the tunnel forward to the firewall. It made the run very easy and I've had no difficulties that I'm aware of.

  

 Wayne Edgerton

 N602WT 

  

  

     Time:  02:40:21 PM PST US    From:  "Bob Leffler" <rv(at)thelefflers.com (rv(at)thelefflers.com)>    Subject:  Transponder antenna location      

      I'm in the process of installing doublers for all of my antennas attached to

      the fuselage bottom.

      

      

      I understand that the transponder antenna coax run should be 3'to 8.8'.   I

      know that some have mounted the transponder antenna in the center tunnel

      near the firewall.  Others appear to have located it under the rear seat or

      baggage area.   Since this appears to require a coax run of longer than

      8.8', I'm curious to what issues (or lack  thereof) folks have experienced

      when they located their transponder antennas in these areas?  Is 8.8' really

      a hard limited from Garmin?

      

      

      Thanks,

      

      

      Bob

      

      #40684



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		  http://www.matronics.com/Navigator?RV10http://www.matronics.com/contribution" target=_blank rel=nofollow>http:========================


	




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