Today's Message Index:
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1. 08:34 PM - Transponder and ADSB antennae question. (Robert Reed)
2. 09:48 PM - Re: Transponder and ADSB antennae question. (The Kuffels)
Message 1
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| Subject: | Transponder and ADSB antennae question. |
I am in the process of locating best place to install the transponder and ADSB
antennae. I have been building for way too long and as a result some things planned
years ago are no longer viable. I initially installed two Archer NAV antennae,
one in each wing. Now I see little or no need for either antennae and have
no plans to install other than GPS.
My question is rather I could disconnect the coax to those antennae, install the
transponder and ADSB in the wing bottom and use the existing coax? I cant remove
the NAV antennae since I bonded them to the underside of the wing top. Will
the old antennae interfere with the transponder or ADSB? Any other issues
to consider? If I later decide to install a NAV system will it interfere with
either unit?
Bob Reed
Message 2
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| Subject: | Re: Transponder and ADSB antennae question. |
Robert,
<< disconnect the coax to those antennae, install the transponder and ADSB
in the wing bottom and use the existing coax? I cant remove the NAV
antennae since I bonded them to the underside of the wing top. Will the old
antennae interfere with the transponder or ADSB? Any other issues to
consider >>
First a confusion. Vanilla ADSB units have only one combined
ADSB/transponder antenna. Why do you need two?
Second confusion. Archer antennas need a metal wing to act as a
counterpoise. How are the Archer antennas bonded inboard of the wing tip.
Either you have a non-metal wing with no counterpoise or you have a shielded
antenna. Obviously there is something here I don't understand.
Potential problems:
By the wing bottom I assume you mean the bottom at the center of the
wingspan. Besides the extra complexity of a remote ADSB unit vs. a panel
mount you are faced with the manufacturers limit on cable length, usually
about 10 feet, because of cable signal attenuation.
Most of ADSB is still ground based. Thus the ADSB antenna needs a 360
degree view of the ground to function fully. At the wing tip much of the
ground (even half) is blocked. This will result in spotty performance and
whines from ATC each time your transponder signal drops out.
ADSB/transponder antennas are ground plane type. A short spike is mounted
on an 8 inch or so circle/octagon/etc. Mounting this antenna with the spike
horizontal and facing outward would shield the antenna from any conducting
metal inboard. But this also guarantees maximum signal blockage. Mounting
the ground plane on the bottom of the wingtip with the spike protruding
downward would work better.
If it were me, I'd mount the antenna on the bottom of the fuselage. On my
Sportsman, it is mounted to the underside of the fuselage cage with the
spike protruding through the fiberglass fuselage shell about 1 inch.
Tom Kuffel
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