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I've always heard that you should orient the antenna on the Crossfire transmitter vertically, with the ends pointing up and down. I've also heard that you should do the same with the receiver antenna (immortal T), but on many builds that is difficult or less durable, so I mount the antenna horizontally on the drone (under an arm, for example).

For the best signal when flying a drone that has a horizontally mounted Crossfire antenna, should I also rotate the transmitter antenna horizontal to match, or is it better to keep it vertical regardless?

It would be great to understand the logic either way as well. Thanks!

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A dipole antenna is linearly polarised, which means it radiates most of its energy in one 'plane' relative to the antenna. For maximum efficiency, the transmit and receive antenna should be orientated such that their plane of radiation is the same, or very close to.

It is important to note that as the aircraft flies around, the orientation of the antenna changes with the aircraft. The reason a vertical orientation is recommended is that aircraft - particularly multirotors - generally1 fly with one side 'up'; therefore, for whichever direction the aircraft is travelling the antenna is still vertical (or, mostly so) compared with the transmitter.

With a horizontally orientated antenna, when the aircraft turns through 90° relative to the transmitter, the antenna is now 90° out of alignment to the transmitter; it may help to think of/visualise this as "North/South" and "East/West", and the loss of signal will be comparable to vertical vs. horizontal as the angle difference is the same. Some receivers have multiple antennas and recommend orientating them at 90° to each other to mitigate this scenario.

What you may consider, if your transmitter permits it, is to have the antenna at a 45° angle as a compromise for signal strength. Most drones have a built-in lost comms failsafe so a loss of signal should not be a huge concern; for a fixed-wing model aircraft, I would be more concerned about matching antenna orientations.

[1] The main exceptions probably being stunt aircraft

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  • $\begingroup$ Good answer, however I don’t think the orientation has to do with polarisation. For example, a dipole antenna is not polarised and accepts RHCP and LHCP signals equally, however there is a dead region running parallel through the long axis of the antenna. $\endgroup$
    – Drones and Whatnot
    Apr 14, 2020 at 21:34
  • $\begingroup$ @DronesandWhatnot You are correct about circular polarisation, however I refer to linear polarisation where orientation does make a difference. (I am not familiar with the Crossfire range specifically, but my searches online have not indicated this uses circular polarisation; and, the pictures generally show dipoles.) $\endgroup$
    – Kralc
    Apr 14, 2020 at 21:36
  • $\begingroup$ I’m not an RF expert, however as far as I am aware that is the directional gain, not the polarisation. For example, if I have an RHCP patch receiver antenna and an RHCP omni TX antenna, if I face the patch away from the TX, the orientation is different and it’s gain is lower, however the polarisation of both the EM waves and the antenna is the same. Again, I’m not an RF expert by any means, this is just how I have always understood polarisation. $\endgroup$
    – Drones and Whatnot
    Apr 14, 2020 at 21:54
  • $\begingroup$ I see what you are saying, and I agree that the type of polarisation isn't changing when you change the angles, just the relative orientation. I've probably oversimplified by referring to the angles as discrete 90° segments; as linear polarisations are commonly horizontal or vertical, I've extended my answer from this. I'll have a go at rewording to try and make this clearer, but still keep it accessible. $\endgroup$
    – Kralc
    Apr 14, 2020 at 21:56
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    $\begingroup$ Not at all; it's good to have another view and it means a better answer. It is difficult to critique your own writing, as you know what it 'should' mean! $\endgroup$
    – Kralc
    Apr 14, 2020 at 22:00
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In theory, both vertical is the best way to go. However, I've got over 2 miles with both antenna's being horizontal without any issues. Crossfire is such a robust signal that, if you are not pushing serious range, you can get away with putting your antennas any orientation and still be ok.

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