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Antennas - transponder and ADS-B

 
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andymeyer



Joined: 31 Mar 2015
Posts: 54
Location: SW MI

PostPosted: Mon Feb 08, 2016 7:00 pm    Post subject: Antennas - transponder and ADS-B Reply with quote

Looking at getting rid of my external transponder antenna and putting two internal collinear 4 element antennas in the winglets of my Long EZ. 
Right winglet already has my VHF com,  so I figured sneaking the ADS-B antenna in there would be okay,  unless having those two that close is bad. Will transmitting on the VHF smoke the ADS-B receiver (stratux)? 
Left winglet would get the transponder antenna. GTX327. Question is I need one interconnect at the wing / fuselage interface and about 25 feet of cable.  Garmin says 1.5 dB loss max in the cable.  Can I succeed here or is this not worth the effort?  I'm trying to get rid of the extra stuff hanging in the wind. Any other suggestions of where to hide the transponder antenna? 
Other question...  Current VHF is wired with rg58 I believe.  Need to replace a section of coax (radio to wing/fuselage joint),  gotta use the same coax type,  right?
Thanks! 
Andy
Sent from my Verizon Wireless 4G LTE smartphone


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kjashton(at)vnet.net
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PostPosted: Tue Feb 09, 2016 5:58 am    Post subject: Antennas - transponder and ADS-B Reply with quote

Transponders do not like any long cable runs. They also want continuous line-of-sight to the radar station. Even mounting an antenna in the nose of an EZ will cause the radar to lose it when climbing away from the station. In a shallow turn, the winglet position could be blocked by the fuel and engine. You might get by with it under your seat or inside the fuselage but it is best on the bottom of the airplane. You just don’t want any metal or liquid-filled bags (i.e. people) between the antenna and the station.

Sure you can change cable types in a run but it’d be easy to strip the old RG-58 out and run RG-400 stranded.
-Kent
LEZ and Cozy

Quote:
On Feb 8, 2016, at 9:58 PM, ameyer <ameyer(at)mil-amax.com> wrote:

Looking at getting rid of my external transponder antenna and putting two internal collinear 4 element antennas in the winglets of my Long EZ.

Right winglet already has my VHF com, so I figured sneaking the ADS-B antenna in there would be okay, unless having those two that close is bad. Will transmitting on the VHF smoke the ADS-B receiver (stratux)?

Left winglet would get the transponder antenna. GTX327. Question is I need one interconnect at the wing / fuselage interface and about 25 feet of cable. Garmin says 1.5 dB loss max in the cable. Can I succeed here or is this not worth the effort? I'm trying to get rid of the extra stuff hanging in the wind. Any other suggestions of where to hide the transponder antenna?

Other question... Current VHF is wired with rg58 I believe. Need to replace a section of coax (radio to wing/fuselage joint), gotta use the same coax type, right?

Thanks!

Andy



Sent from my Verizon Wireless 4G LTE smartphone



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nuckolls.bob(at)aeroelect
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PostPosted: Tue Feb 09, 2016 5:58 am    Post subject: Antennas - transponder and ADS-B Reply with quote

At 08:58 PM 2/8/2016, you wrote:
Quote:
Looking at getting rid of my external transponder antenna and putting two internal collinear 4 element antennas in the winglets of my Long EZ.

I presume this antenna will have been
qualified for performance?

Quote:
Right winglet already has my VHF com, so I figured sneaking the ADS-B antenna in there would be okay, unless having those two that close is bad. Will transmitting on the VHF smoke the ADS-B receiver (stratux)?

It might de-sensitize it but won't damage it.

Quote:
Left winglet would get the transponder antenna. GTX327. Question is I need one interconnect at the wing / fuselage interface and about 25 feet of cable. Garmin says 1.5 dB loss max in the cable.

More than the "allowed loss" simply means that
you are less likely to be an active target
on the radar screen at extreme range . . .
which probably accounts for a tiny percentage
of operational conditions. But the distance
from the panel of an EZ to the wing tip is
substantial.

There is a handy cable loss calculator you
can exercise at

http://tinyurl.com/grzxvh8

As a WAG, assume 20' of RG58 at 1500 MHz
gets you 4 db of loss assuming only connectors
on ends . . . wing root connecter will add
a tad more. However, a run of LMR400 would
probably meet the 1.5 db loss target with
the extra connectors.


Quote:
Can I succeed here or is this not worth the effort? I'm trying to get rid of the extra stuff hanging in the wind. Any other suggestions of where to hide the transponder antenna?

The drag of the classic transponder antenna
would be hard to measure . . . you can calculate
it but it's pretty tiny. Whether or not it's
'worth it' is a judgement call. I have posited
that question about converting to lithium batteries
as well. In ten years or so, we'll probably have
enough builders with lithium track-records
that we can begin to put practical numbers
on 'worth it'.


Quote:
Other question... Current VHF is wired with rg58 I believe. Need to replace a section of coax (radio to wing/fuselage joint), gotta use the same coax type, right?

Nope, you can run mixed 'types' as long as
they are 50 ohm.


Bob . . .


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berkut13(at)berkut13.com
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PostPosted: Tue Feb 09, 2016 7:17 am    Post subject: Antennas - transponder and ADS-B Reply with quote

I’ve had good results putting the ADS-B antenna inside the nose of EZ-types. In the Berkuts, I put a simple rod/ball antenna inside the nose wheel well, next to the strut, as low to the floor as possible – no ground plane needed for receive only. Others I have put in the nose area, as low to the floor as possible – just try to imagine a shallow cone emanating from the antenna toward the ground and place it as free of obstructions as possible. I even ground out a depression in the nose floor sometimes to allow the ball of the antenna touch the external skin.

I’m not a big fan of putting the xponder antenna anywhere other than the outside of the belly. As Ken points out, you get line of sight blockage anywhere else. The best place I have found is the aft floor above the belly brake with a hole in the brake to allow the antenna to pass through. It is easiest to install, gives best performance, and does reduce 1/3-1/2 of the antenna’s drag area profile.

http://www.berkut13.com/berkut30.htm#transponder

If you insist on internalizing it, I would recommend the wing/strake D-section pocket instead of the winglet. You’ll get similar blanking issues but it’s far easier to install in that location with a small ground plane. (not a fan, but workable)

-James
Berkut/Race 13




From: ameyer (ameyer(at)mil-amax.com)
Sent: Monday, February 08, 2016 8:58 PM
To: aeroelectric-list(at)matronics.com (aeroelectric-list(at)matronics.com)
Subject: Antennas - transponder and ADS-B


Looking at getting rid of my external transponder antenna and putting two internal collinear 4 element antennas in the winglets of my Long EZ.

Right winglet already has my VHF com, so I figured sneaking the ADS-B antenna in there would be okay, unless having those two that close is bad. Will transmitting on the VHF smoke the ADS-B receiver (stratux)?

Left winglet would get the transponder antenna. GTX327. Question is I need one interconnect at the wing / fuselage interface and about 25 feet of cable. Garmin says 1.5 dB loss max in the cable. Can I succeed here or is this not worth the effort? I'm trying to get rid of the extra stuff hanging in the wind. Any other suggestions of where to hide the transponder antenna?


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