Drag of Transponder Antennae compared

On Thursday, 11 February 2021 at 05:10:10 UTC, Kenn Sebesta wrote:
On Wednesday, February 10, 2021 at 5:47:39 PM UTC-5, Bob Hills wrote:
Thinking totally outside the box here and open to ridicule :).....

Blade antennas are similar in shape and size to a winglet. Why not incorporate the antenna in that? I know it would mean an electrical connection from tip to fuselage but that is not insurmountable.

Just a thought for someone to expound upon.

Bob 7U
I think you could do that, but there are a couple challenges

1. RF cable is heavy and significantly affects the signal. On sailboats, it's suspected that a stern-rail mounted VHF radio antenna actually performs better than a masthead mounted antenna. So sending it 5-10m to the wingtip instead of keeping it close to the TX unit could noticeably decrease range.
2. Even when in perfect shape, RF connectors are a big source of energy loss, which further reduces range.
3. The connector would have to be properly connected/disconnected every time the plane is pulled out of its trailer. A powerful RF transmitter which is disconnected from an antenna can actually destroy itself, so the consequences of a forgotten connection are not necessarily limited to only being invisible that day.

Cable losses per metre are greater with higher frequency. This is why systems such as satellite TV and even some terrestrial TV installations convert to a lower frequency before the downlead.

Transponders are working at UHF, and hence a short antenna cable distance is desirable, and the unit may be remote mounted in the centre section rather than in or behind the instrument panel.

Winglets are probably made of carbon fibre, so the antenna would be screened and not work inside.

I'll consider putting the transponder antenna inside a glass fuselage, and wonder how far from spaceframe and control rods/cables is desirable or feasible. Might need some contortionism to fit it. Might end up outside anyway.