REFLECTOR: Transponder cable

Dwight hummer31 at netzero.net
Tue Feb 26 21:06:13 CST 2008


All

I am not sure if this is the preferred method of responding or not.  If not 
please let me know

As far as a good cable for the transponder connection, go to 
http://www.smelectronics.us/smasmarficables.htm and select the LMR 240 cable 
(.08 dB/Ft @ 1 Ghz).  You can order the desired length needed up to 10 ft 
plus with standard connectors.

Dwight
----- Original Message ----- 
From: <reflector-request at tvbf.org>
To: <reflector at tvbf.org>
Sent: Tuesday, February 26, 2008 9:16 AM
Subject: Reflector Digest, Vol 45, Issue 86


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> Today's Topics:
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>   1. Re:  Transponder Antennas (John Tvedte)
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> ----------------------------------------------------------------------
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> Message: 1
> Date: Tue, 26 Feb 2008 10:14:46 -0600
> From: John Tvedte <johnt at comp-sol.com>
> Subject: Re: REFLECTOR: Transponder Antennas
> To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
> Message-ID:
> <6A72C624AAB4824C90802D479E8DB8C3431870DFFF at airmail.comp-sol.com>
> Content-Type: text/plain; charset="windows-1252"
>
>
> Craig,
>
> Attached are the cable spec requirements for the GTX-330.  Note that max. 
> loss in the cable is not to exceed 1.5db.
>
> Typical RG400 attenuation @ 1000Mhz is .169438 db/ft.  Garmin specifies 
> 8.8 ft max = 1.491057.  (The transponder is actually 1090Mhz).
>
> Typical RG58c/u attenuation @ 1000Mhz is .222748 db/ft.  One can divide 
> this by 1.5db = 6.734 ft.
>
> I would check your cable lengths - and make sure you are within length 
> limitations for the cable that you used based upon attenuation at the 
> transponder freq.
>
> You may be getting signal blockage - the area the factory suggests placing 
> the transponder antenna is a good location - but with a GTX-330 one will 
> need to use a low loss coax.
>
> John
>
> Please check with the radio shop regarding the antenna.
> I understand that that the Garmin 330 requires a special antenna; using a 
> high quality transponder cable.
> I don't think that a home-made or Archer type transponder is going to work 
> with the 330.
> SB
> ----- Original Message -----
> From: Craig and Denise Woolston<mailto:cdwoolston at sbcglobal.net>
> To: 'Velocity Aircraft Owners and Builders 
> list'<mailto:reflector at tvbf.org>
> Sent: Monday, February 25, 2008 8:05 AM
> Subject: REFLECTOR: Transponder Antennas
>
> Hey all-
>
>  John and I have a homemade ? wave transponder antenna mounted under the 
> battery in the nose of the aircraft (completely) inside.  When we first 
> started flying we got occasional complaints here in SoCal about losing our 
> beacon.  Now it happens much more frequently and it appears to be when we 
> are low and in the ?ground clutter?.  The frustrating part is the GTX 330 
> shows a reply light even when ATC says they can?t see the code.  They are 
> getting a primary but no code.
>
> Where have other located their antennas and what type?
>
> Has anyone tried the Archer or Advance Electronics Antennas I see in AS?
>
> Craig
>
> 250hrs?XL-5FG Flying in Lancaster, CA
>
>
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