Antenna placement

[Gripdana]

Hi Robbie,
I put the comm on the belly under the seat. The ELT on the turtleneck and the transponder one bay back from the baggage on the belly.

[Sonex1517]

Holy old thread resurrection Batman!

Thanks for the info everyone.


Robbie Culver
Sonex 1517
Chicagoland
Tails and Wings complete - finishing fuselage.
N1517S reserved

[kmacht]

One more thought. I put mine just forward of the wing spar. The connector fit perfectly under the flap torque tube so there was no worry of hitting it with your feet. This made it so I only had to run the coax along front edge of the spar box and then up to the panel keeping me from having to try and run coax from behind the seat, over or through the spar, and to the panel.

[Gunther]

There is another consideration for antenna placement from a health perspective - the image antenna on the inside of the aircraft. A typical monopole antenna creates an image on the inside of the aircraft, analogous to a mirror image. Since this image antenna also radiates energy, one might want to place the antenna as far away from the crew as possible. On the other hand, antenna position may not be too critical when considering reflections and waveguide effects within the fuselage. Any antenna experts out there who could enlighten us?

Gunther

[Bryan Cotton]

I believe the antenna behaves as though there is a mirror image but that RF is not running around inside the tailcone. Also, the duty cycle of how much we transmit is very low.

[gammaxy]

A typical monopole antenna creates an image on the inside of the aircraft, analogous to a mirror image

The mirror image is not actually inside the aircraft. It's more like when you have a polished aluminum airplane and can see a visible reflection of the antenna in the skin. To the outside world, it might look like there is an upside-down antenna inside the airplane, but if you go inside the airplane you won't find the "virtual antenna". The radio signal behaves similarly--you won't find it inside the fuselage except for the relatively small leakage and whatever enters through the canopy.

[Gunther]

Chris and Bryan, thank you for taking the time to set me straight. I'm considering a bottom mount antenna to leave the top free for a slider canopy.

Gunther

[wlarson861]

I have a bottom mount com and transponder antennas due to having a swing back canopy. The only time I couldn't be heard was when trying to contact ground control from the far end of the field at an unfamiliar airport. Tower heard me all the way in and ground heard me on the ramp to leave, figure it was position of ground antenna relative to plane.

[Onex107]

My understanding of the com antenna is, it's a quarter wave antenna and the wave extends from the tip of the antenna to the ground plane, which in this case, must be a metal surface. On a rag and tube airplane you must provide a metal surface of a specific diameter. On my Onex. I mounted the antenna on the turtle deck close to the rear of the cockpit and I have poorer reception forward, which I attribute to reduced ground plane forward. The length of the antenna relates to the frequency range it works with. I'm not aware that anything exsists below the the ground plane.
Old radio operator.

[hickej]

I ended up moving my antenna from the bottom to the top to get it as far from the engine as possible. I have a Waiex and an MGL V6 radio. I was getting interference when trying to receive which cut my effective range down to less than 7 miles. Once I moved it back I got perfect reception from at least 20 miles. Consider putting it far back past the sliding canopy. IMHO