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Transponder antenna location forward of center section

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davidl409(at)comcast.net
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Posted: Sun Sep 23, 2007 8:51 am Post subject: Transponder antenna location forward of center section

I’m building a 601XL from kit and at about 85% complete. I am looking for a good place to install the transponder antenna forward of the center section. I have installed the gascolator just in front of the center section in the middle so that area isn’t available. Will the nose gear block reception if I locate behind it?   

   

David Lautenschlager  

Mobile, Alabama  

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dredmoody(at)cox.net
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Posted: Sun Sep 23, 2007 10:07 am Post subject: Transponder antenna location forward of center section

As a general guideline, the transponder antenna  should be located so as to (A) have as short a feedline form the transponder as  possible and practical, (B) be a couple of feet or so from other sensitive  instruments which might pick up the short intensse bursts of its transmission,  and (C) be at leat three feet from other antennas, (transceiver, localizer, VOR  etc.).

  

 The center C-channel under the cabin floor is a  satisfactory place to install the transponder antenna and unless it is  immediately behind the nose gear it should function well. I would place it  at least a foot or so back from the firewall to be safe on that  account.

  

 I decided while building the fuselage that there is  so damned little room for wiring to traverse fore and aft through  the center section of the spar, that I would close the center C-channel support  under the cabin by making a cover for it. The cover is retained by #6-32  flathead screws and nutplates. The cover allows the use of that center C-channel  to run my brakelines back to the main gear legs, and to run wiring  under the cabin floor and the center section of the spar rather than  trying to run everything through the one small hole in its center.  That hole already accomodates the aileron torque tube, the rudder cables,  and the threaded rod from the center stick assembly to the elevator control horn  inside the console. 

  

 Because of that adaptation, the center C-channel  was not a convenient location for me. I decided instead to mount the transponder  antenna in the cabin floor through the rudder pedal bearing channel  and centered between the left seat rudder pedals. The pedal bearing channel  eliminates the need for a doubler to support the antenna. That location places  the feedline coax cable between the pedals where it doesn't physically interfere  with their movement and puts the antenna a satisfactory distance from  anything it might interfere with in the RF sense. It also routes the cable where  nobody's feet are likely to traumatize it over time. Regardles of whether or not  you use the exterior C-channel as I did or not, this site in the pedal bearing  channel, centered between either set of rudder pedals remains a decent  option in the 601XL.

  

 In the photo the antenna connector and the coax  feedline can be seen between the left side rudder pedals. The gizmo  immediately forward of the antenna is a Matco parking brake valve. The  brakelines can be seen running from the valve outlets to where they exit the  cabin into the center channel conduit.

  

 I hope this helps you. Drying out yet?

  

 Dred

 601XL/Jabiru

 Rayne, LA

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Trainnut01(at)aol.com
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Posted: Mon Sep 24, 2007 2:33 am Post subject: Transponder antenna location forward of center section

Dred

 The C-Channel sounds like a wonderful idea. Do you have any pictures of  that installation?

 Thanks 

 Carroll

  

 do not archive



See whtarget="_blank">Make AOL Your Homepage.

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