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corosplat

Antenna for 868MHz

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Hello,

I'm looking for ideas for an antenna on the airborne side of a UAV project to connect to an Aerocomm AC4868-250 radio modem module (mmcx antenna connector). It would be nice to get a commercial unit, but the ones I have found so far are a bit large and clumsy for integration in a small UAV. Home-brew copper foil/coax projects are also of some interest.

/Steve

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I suggest trying a simple 1/2 wave dipole (simple to make). If your model can accommodate a 1/4 wave ground plane antenna (www.northcountryradio.com/Articles/groundplane.htm) then that should offer a tiny bit more performance. Beyond that, a cross-dipole design (http://www.aricraft.com/spiro.html) would be very nice, but they can be difficult to get right.

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Generally speaking, antennas with PCB dielectrics have lower possible gain. They are usually more compact though.

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Just to clarify.. when you say simple half-wave dipole, you mean like the one in the RC-CAM4 project? Made from coax stripped to the right length with the shield folded back. At 868MHz the elements would be about 8.2cm long for a total length over 16cm right? Does it matter how much "extra" coax I have besides the antenna element itself or is that a trial and error thing.

Also as for mounting in the plane, I guess it would be best to have it pointing down, but given the length, would it be OK to lay it flat, or at least angle it back?

thanks,

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The coaxial design on RC-CAM might work out for you, but I was actually referring to a classic dipole. These are constructed with two 1/4 wave (82.9mm) elements that are center-fed. If you need to see drawings, I suspect that you will find endless info on the web.

Generally speaking, Tx antenna orientation depends on the orientation of your ground based Rx antenna.

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