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ADS-B and Transponder Antenna Radiation Concerns

 
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billhuntersemail(at)gmail
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PostPosted: Sat Apr 15, 2017 7:46 am    Post subject: ADS-B and Transponder Antenna Radiation Concerns Reply with quote

Hi All,

I am building a radio rack/shelf in a Velocity (fiberglass pusher) and I am thinking of getting creative in the installation location of the ADS-B and/or transponder antenna location so as to reduce antennae farms under the airplane and the resultant drag.

I was considering mounting the transponder and/or ADS-B antenna upside down under my newly built radio shelf that will be installed on top of the “canard” in the “canard doghouse”.

In the Velocity pusher design, the “canard” is the front wing of the airplane and the “doghouse” is the space above the canard center section and it is essentially a large faring that streamlines the airplane nose and fuselage to the canard. The design is such that the canard mounts to the airplane in front of the windshield and it is installed pretty much directly above the pilot/copilot foot well (above the rudder pedals).

See attached picture of partially built radio shelf and this view is as if you were looking down from the windshield to the top of the canard center section (doghouse) and directly below this radio shelf would be the pilot/copilot foot well and rudder pedals.

I could drill a hole in the aluminum shelf and install the antenna (antennae) sticking straight down below the aluminum sheet metal and that would require drilling a vertical hole straight down through the canard skin and foam (making sure to avoid drilling through the canard spar). That area of the canard is not considered to be a structural component because the canard has a main spar and this is just a fiberglass skin/foam core/skin sandwich construction.  The antenna would pretty much be completely inside the fuselage envelope and surrounded by foam and fiberglass and the aluminum shelf would act as the ground plane.


My electrical concerns are:

-Is having a high frequency transponder antenna mounted 24 inches above my feet a good idea?

-The ADS-B antenna is a dual band receive only antenna so if I just went with the ADS-B antenna mounted above my feet there would not be a concern of irradiating my feet however the other concern would be the interference of the metal rudder pedals and the metal control linkage below the antenna interfering with its signal. Would that make the ADS-B reception less sensitive?

Just some thoughts to ponder for the transponder.

THANKS!!!

Bill Hunter


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Location: Riley TWP Michigan

PostPosted: Sat Apr 15, 2017 10:48 am    Post subject: Re: ADS-B and Transponder Antenna Radiation Concerns Reply with quote

Quote:
Is having a high frequency transponder antenna mounted 24 inches above my feet a good idea?
I do not know, but probably is a bad idea.
Quote:
Would that make the ADS-B reception less sensitive?
Yes, but probably not significantly. I would install the receiving antenna wherever you want, then try it out. You can always move it if necessary.


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kjashton(at)vnet.net
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PostPosted: Sat Apr 15, 2017 12:03 pm    Post subject: ADS-B and Transponder Antenna Radiation Concerns Reply with quote

Quote:
On Apr 15, 2017, at 11:14 AM, William Hunter <billhuntersemail(at)gmail.com> wrote:


I was considering mounting the transponder and/or ADS-B antenna upside down under my newly built radio shelf that will be installed on top of the “canard” in the “canard doghouse”.

The transponder antenna must have line-of-sight to the radar station with no engines, avionics or people (bags of water) in between. When departing a radar station at say 5000 AGL and 25 NM, the look angle from the airplane to the station is only about 2 degrees down so the antenna almost has to go on the bottom of the airplane.


Even fiberglass builders who mount them in the nose have problems keeping radar contact on departure. A 2 degree angle of attack and 1 degree climb angle puts the passengers between the antenna and the radar station.

It is fine to mount the antenna under your seat or under your feet. The transmit pulse is so brief that it has negligible effect. My ground plane in under the seat and the antenna sticks out the bottom of the airplane.
-Kent


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