The quad I'm building will be controlled on 2.4Ghz (rec.), not sure what the antenna on the receiver will look like, or if I can upgrade to an SP antenna. It's a Turnigy 9x.
It'll have 1.2Ghz FPV transmitter, and 915MHz telemetry transmitter (and GPS)
The quad frame has a very large deck -- about the size of a sheet of letter-size paper, so I can put antennas in each corner, with the GPS in one of the back corners.
My question is: Which two antennas are best located farthest apart? (in opposite corners of the deck) I can managed a FOOT of separation between two of them, and eight and ten inches between the others.
Would it be the two transmitters? Or the 2.4 & 1.2GHz?
And is there any issue with using circularly polarized antennas on all three?
Replies
I would put the receiver and GPS antennas as far as possible from the two transmitter antennas. The GPS will be mounted on the top and hopefully in a vertical rod to distance it from all the noise producing electronics. The receiver can be mounted either top or bottom and not too close to the high current motor traces or wires.
The transmitter antennas don't require as much spacing, as a 1/4 wavelength of 1.2 GHz is only about 2.3 inches. So anything over 3-4 inches won't affect the radiation pattern much.
If you can, it may be a good idea to use ccw polarization on one of the one of the transmitters and cw on the other since the 2.4 GHZ is a harmonic of the 1.2 GHz frequency. Just be sure that have matching receive antennas on the ground.
I used to design microwave systems for news helicopters and we had a transmitter, receiver and 3 microwave antennas in a pod mounted underneath the ship and could shoot 60+ miles of video with 10 watts. It could receive live video from a ground TV van and retransmit it on another channel back to the station when in poor location.
Curious about this, Gordon - what exactly is the significance of 1/4 wavelength?
My naive guess would have been that a full wavelength of distance between antennae would be a significant value, or maybe 1/2, but what's special about 1/4?
Thinking of trying to apply some of your advice on my 5.8/2.4/915 setup, as I moved some antennae around and lost quite a bit of range on my telemetry.
Thanks for your input Gordon.
I'll try to implement your suggestions. As I get things finished and fired up, I'll know how well I've succeeded or how badly I've failed. Then I'll adjust as needed. Fortunately with a fairly large platform, I'll have quite a bit of room for adjustment. Not like the 'X' quads with the tiny platform in the middle.