Tandem Rx Antenna placement on carbon glider

[davesieger]

I'm eager to try the new Tandem Rx however I'm not sure how to mount the 900MHz antenna. My thoughts are to mount the 2.4 antennas as I normally do protruding from the top of the fuse and the 900 on the bottom of the fuse parallel to the boom. If that placement is functional my next step will be to print a faring to assist in aerodynamics and protect it during landings.

Thoughts???

 

[Nigel]

Is your fuse carbon? Also, what kind of plane is it? Generally the rule of thumb for all antennas (but 900 even more so) is stay away from carbon, and place your antenna vertically. The second part of that is situational if you fly F5J or the likes, something where you spend more time almost directly above yourself than far away and low down. If at all possible I would avoid putting it parallel to the boom, perpendicular is much better. The influence that carbon fiber (or anything radio-active) has on an antenna is the least in the middle of the antenna, and the worst towards the tips due to higher current density.

 

[Nigel]

And a small infographic on the current density effect

 

[davesieger]

Yes the installation will be in a 4M carbon F5J model. Nothing easy about this installation as space is a minimum, the airframe is clean and the all up weight for the model is 1105g.

Thanks Nigel for the information! I was afraid that would be the case. Parallel to the boom is better aerodynamically than perpendicular. I wonder if keeping the antenna perpendicular but 1/2" away from the boom would be an improvement? Surely there is an acceptable antenna placement for these competition gliders, even though it wont be optimal.

 

[Konrad]

Balancing the various variables can be a challenge. But in this case the RF concerns trump any aerodynamic concerns as F5J is a low speed event often flown at great distance. The area covered ranging looking for lift with a properly installed antenna far far out weigh any loss to drag. Just take a look at all the antennas we see sticking out of super sonic aircraft to understand just how important antenna performance really is.

 

[Nigel]

You will notice a large improvement moving even just half an inch away if parallel to the boom (inverse square law), but you will still be nowhere near optimal antenna performance. An option that might satisfy your desire for low drag would be to substitute the bulkier stock antenna for a stripped down version. You'll need to devise your own method to keep the antenna rigid, I like some thin plastic tube and heatshrink. Antenna found here, just make sure that the tandem also uses an UFL connection.