2500MM RC drone -- What's the absolute furthest it can go with legal powerful antennas? (and which ones!)

Anis Nielsen September 20, 2011 at 5:20pm

Try and watch this video if you didn't already; It helped me understand the many hurdles and ways of bypassing them :

Someone posted this on diydrones but i cannot find the post :

Antennas 101 - Polarization, Diversity & Gain Patterns

Antennas 101 - Polarization, Diversity & Gain Patterns from Andy Lawson - www.JoopMedia.tv on Vimeo.

Andy Creighton September 20, 2011 at 5:02pm

Ahhh thank you so much Mr. Mills. (The intellectual level of the people on this site continues to amaze me. A true gem of the web.)

I see what you are saying, that was the most complete answer I have gotten in terms of anything on the internet by the way. So in practice using a medium gain antenna pointed in the general direction of the drone with an omnidirectional receiver on the plane is not practical.

(And just to cover all possibilities...) Using a high gain antenna, and creating a system where it automatically tracks the plane and adjusts when the plane moves about the foreground of the antenna...about how high of a gain of an antenna would I be able to pull off if I needed to be able to put it in the air, send it 50 miles north, document a scene(rather quickly) and return back. Assume I have the battery life AND the base antenna altitude of operation figured out(I'm laughing too but my style is ambition so work with me).

I am willing to engineer around roadblocks if i must..so forgive me if I twist and tangle RC talk and traditional means of operation.

Andrew

Toby Mills September 20, 2011 at 2:52am

There is no such thing as a powerful antenna. Only antenna gain. The higher the gain the narrower the field of operation but the further it will travel. Think of it like a candle. All the light from a candle spreads out equally in all directions but it is not very bright. However, if you used a mirror you could block the light going in one direction and reflect it in the opposite direction which would increase the light in one direction and decrease it in the other.
Taking it even further, if you squashed all the light from a single candle into a narrow laser beam it would be very powerful (compared to the original candle) but also very narrow.

The higher an antenna's gain the further it can send / receive a signal but the narrower its directivity.

If you were to mount a very high gain antenna on a plane it could transmit over a very long distance but you would have to point the antenna at exactly the location you wanted to pick that signal up from.

Think of it like the voyager spacecraft which is millions of miles away from earth. It is able to send it's data back to earth using a relatively low power transmitter but the antenna adjusts so the signal is pointing at the earth.

If you could do the same on a plane then there is no reason why you could not transmit 100km plus ranges using low power transmitters. However in practice this is not very practical. So in general we use omni directional antennas in the plane which send the signal in all directions equally (candles) and put a high gain antenna on the ground that must be pointing at the plane to pick up the signal (lookup antenna tracking threads).

The higher the gain of the antenna on the ground then the more accurately you must point the antenna at the plane in order to pick up the signal but the further that signal can be transmitted / received.
A low gain antenna can be compared to a floodlight, you just point it in the direction of the plane and it will light up, but it doesnt work for a long distance.
A medium gain antenna is like a flashlight, it's reasonably easy to track the plane as the beam is quite large so there is a reasonable spill.
A high gain antenna is like a laser beam, try tracking a plane with a laser pointer and see how hard it is.

Not a simple answer to your question but hopefully you can see the answer is really...
It depends

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2500MM RC drone -- What's the absolute furthest it can go with legal powerful antennas? (and which ones!)

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