FPV: Equipment For FPV

Circular Polarized Antennas

 

What is Circular Polarization?

Scientific Interpretation –

“Circular polarization of an electromagnetic wave is when the field of a passing wave does not change strength but changes direction in a rotary manner. “

We apply this theory when discussing circular polarized antennas in FPV flying. Circular Polarization is a huge step forward in the progression of the FPV experience as it brings a vastly improved signal and video reception to the FPV RC vehicle.

Circular polarization is the preferred method of control when flying FPV. The use of circular on both system ends nearly eliminates interference which is the number one cause of video drop outs. With circular polarization you get a predictable and consistent video link which does not lose its polarization whilst in flight.  Also with circular you get a lot more power to pass through objects such as trees and houses.

Depending on how you have the antennas polarization set up it can sometimes come out in a clockwise or anticlockwise circular pattern. This is known as right hand or left hand polarization. If you look at the picture you can see that when the antenna is positioned horizontal, vertical or anywhere else in between the signal that is released is actually the same.

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What is Linear Polarization?

Antennas sold with video transmitters and receivers are linear polarized. Linear means straight, with the signal coming out between each end of the antenna and usually in a vertical wave.

Linear polarization can go up to 40% further than circular but many times there are outside issues that cause problems with linear polarization which make its full range unrealisable at low antenna gains. For high gain and extreme long range systems, Linear is comparable to circular if not better.

With linear polarization the advantages lie in that products are small, cheap and plentiful.

Below you’ll see what’s called a vertically orientated antenna with N acting as the top of the antenna and S acting as the bottom. The waveform emits from top to bottom in a linear fashion to achieve Linear Polarization.

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Mixing Polarizations

Mixing polarizations can prove to be less than optimal and in some circumstances it may be desirable to keep a circular antenna on the ground and a linear antenna in the air. You would choose this set up when the size of the TX antenna would make circular polarization difficult.

Here’s An Educational Video On Circular And Linear Polarization:

Multipath Interference:

Scientific Interpretation –

“Multipath Interference is a phenomenon found in the physics of waves whereby a wave from a source travels to a detector via two or more paths and, under the right condition, the two (or more) components of the wave interfere. This has been known to cause what is known as “ghosting” in analogue television broadcasts.”

We apply this theory to FPV as it is similar to the above definition. Multipath Interference is when the linear signal deflects off of an object and returns to the receiver later than expected or out of point with the original intended pattern. This happens because the receiver antenna still matches the transmission. Circular polarization reduces this problem dramatically. When the pattern is bounced off of an object what does happen is that it changes its pattern from left to right hand or vice versa depending on what transmitter and RC vehicle you are using. It is now opposite transmitted polarization so practically all the signal ends up missed or rejected.

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Thanks for reading!