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Old 02-04-2019, 06:08 AM
BH1166 BH1166 is offline
Join Date: Nov 2017
Location: Eatonton Georgia
Posts: 410
Default TED Transponder vs 978MHz TED

Previous owner had a NavWorx unit installed. Transponder uses a Delta Pop and there is a TED on the belly as well. How would I determine if the correct TED is installed e.g. the 978MHz version ? I am thinking the length of the antenna may make it a transponder vs 978MHz changing the bandwidth, but just a guess. Would like to use it if possible for the EchoUAt unit I am getting ready to install. The TED is mounted in the tail pop just behind the firewall.
RV6A Purchased N72TX
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Old 02-04-2019, 07:32 AM
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GalinHdz GalinHdz is offline
Join Date: Mar 2010
Location: KSGJ / TJBQ
Posts: 2,191

A transponder antenna will be about 1/4" shorter (2.659" vs 2.408") than a 978MHz antenna, so shorter but not by much.

Even though others here will swear it is a disaster waiting to happen, for our application you can use it with no problem. Now, if you are in a controlled laboratory environment with sensitive measuring equipment then you will notice an improvement with an antenna cut specifically to 978Mhz instead of 1060Mhz. But with a good installation you really won't see a difference in operations.

FWIW I have been using a regular transponder antenna for my 978UAT receiver since 2013 and get the same reception as others, flying with specifically designed ADS-B antennas. At the end it comes down to a decision based on costs, ease of installation and looks more than anything else.

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Last edited by GalinHdz : 02-04-2019 at 11:29 AM.
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Old 02-04-2019, 07:37 AM
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10builder 10builder is offline
Join Date: Jul 2006
Location: Nashville, TN
Posts: 142

TED transponder antenna length (base to tip) is 2 7/16” long whereas the TED ADSB antenna length (base to tip) is 2 21/32” long which is a difference of about 7/32 if my math is right. The antenna specs can be found on the ACS site.

....or basically what Galin said!
Brian S.
Arrington, TN
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Old 02-04-2019, 08:09 AM
BH1166 BH1166 is offline
Join Date: Nov 2017
Location: Eatonton Georgia
Posts: 410

Thanks Galin and Brian for your response. I have pulled the specs for both from ACS. I just pulled out the documentation on the NAVWORX and it says use either a RAMI AV11 or RAMI AV74. YEAH ME ! No sliding down the tail cone to replace. I willl measure it to be sure. Again thanks!
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