I have been thinking of ways to increase the range of the data modem or video feed from a UAV. And it always comes back to having better directional antenna on the ground that has to be pointing at the UAV. My problem is I don’t know too many people that would love to come with me to some remote area and hold a stick up to the sky with an antenna on it and point it at a UAV for hours at a time! I can’t see why?? :)

Then I thought it can’t be that hard to make a tracking antenna, can it??

Putting the mechanics of it aside for a moment….
If you had a GPS receiver on the ground (base station), and the feed from the UAV’s GPS it could be done. If you edited the Ardupilot code (another version running on the ground just for the antenna control) so that the GPS data from the UAV was constantly updated into the waypoint 1 position, and changed the rudder part of the code to give you a 360 degree value. This would give you the direction to point the antenna. Then all you would need is the difference in altitude between the two GPS units (Ground and UAV to get the height of the UAV), and then the distance to waypoint data to calculate the angle that the antenna would need to be pointing up from the ground. (Tan- x = altitude/distance I think?) Then all you would need is a reference to north (Compass module) to make sure it all syncs up. Somehow…
The only problem is if it lost track of the UAV it wouldn’t be able to find it again. Hmmmmmm..

This could even be used in a car following a UAV as long as the car was level and not going up or down a steep hill. I guess you could compensate for that as well if you had enough time on your hands.

I found this but there is not much info.

The hard part would be physically building the antenna mount.
I not planning on actually doing this anytime in the near future as I am still trying to build a working UAV but, can anyone think of a better way to do this?

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Based on what you are doing...(btw, you only need a modem or transceiver for 2 way comm, you just need a transmitter and a receiver. that should make things easier and cheaper)

the easiest way is transmitting your GPS coordinates and heading back to the antenna and doing some not so simple, but doable trig, even with that tight band. Having the way points uploaded is a good idea in case you lose your UAV if it slops out of that 8 degrees. antenna will move to where you need it to be, and you just fly around. you only really need 1 GPS. Just put your plane next to the antenna, and let the antenna know this is the "home" position. A compass is a must, but you can get away with a stepper motor and a hand held compass, if you start the antenna facing north every time. After that, things gravy. I doesn't know how big your UAV is but your transmission power is going to play a HUGE factor...

Actually, i should mention. Gain only increases, i guess the tuning. You want something with a HIGH POWER first. That is why i picked the router that i did and then picked a mid gain 10 dbi antenna. The router has a built in amp AND with DD-WRT, i can push the transmission levels without going too crazy on the mW of power. Then again, i'm streaming video and controls, you are just streaming data. you can probably get away with an FM channel and PPM your data. That should give you the range you seek, with low power requirments. UHF is also an option, seeing that communication is one way. You just keep the channel open and everything receiving. Either of these options, you'll need an LCD to tell you what is going on.

then again, 400ft is the max of unmanned flying according to the FAA...and you will need a ham radio license.

You hit the scope of my knowledge i my research on radio TxRx though...i only did it for 2.4Ghz, and i only was doing it for a certain distance so that i would remain "in control" and the FAA wouldn't screw with me.
Having something in the antenna to keep the antenna moving during a loss of signal is a great idea. It would require some sophisticated logic though, especially if the aircraft has special logic for loss of signal (like return to base).

A way to automatically incorporate all this logic in your antenna, would be to run a simulation of the aircraft inside the antenna's pointing computer. If you load the exact same software that you have running in the airplane into the simulation (control laws, navigation algorithms, waypoint data, etc) then you should be able to predict with a high degree of accuracy where the plane will be, and thus, where the antenna should point.

This is useful not just for the case where the signal is lost. If you only get position updates ever 20seconds from the aircraft, you could use the simulation to figure out where the antenna should be pointing for the 19seconds after the receipt of the position packet. It is basically a great smoothing function. Then when each new packet comes in, you can update the simulation with the latest data.

Ideally this simulation would run a little bit ahead of where the aircraft is in real-time...and packets that come in would be a little behind real-time. This would necessitate some catch-up functionality in the simulation. On way to do this would be to save the state of the simulation each (or every few) frames in a ring buffer. Then when a packet comes in, go back to that state, put in the new data and run the simulation faster, to catch up to being ahead of real-time. It might be best to do this with a couple of threads of execution...so you don't have jitter during this catch-up period.
well, you don't need to do that exactly. If the aircraft pulses it's location you just need it to have the craft centered in the beam. I dont' remember the excat equation, but 2*pi*(distance to the plane form antenna)*(effective Tx/Rx degrees)/360 should give you a great approximation of how far the plane has to move from one end of the spread to the other. If you keep the plane centered, then you have half that distance. Then, all you have to do is figure out how fast your plane is going. Basically you will find that there is a max speed that the plane can go at a given distance where a 1Hz GPS will the at the outskirts of the Tx zone if it was moving tangent to your antenna. A little algebra will give you a simple equation. At that point, you can simply just put it in the code and you're set. If you can't accomplish that in 1 second, then you need a 5Hz GPS and you can do it faster. however...let me do a quick calc.

60mph is 88fps. assuming you have it always centered, then you need ~176ft to be your arc. let's make it 180 because, that is already an approximation and tis not too bad to have a small factor of saftey )plus its an easy number to work with). 180*360/(8*2*pi)= 1289.16ft away. Basically, if your plane is s just under a quarter mile away from you, moving tangent, or 90 degrees from your receiver, at 60mph, you are border line from losing comm with it.

Wow that was actually reassuring...

at that point, if you can't get an omni direction antenna to cover you from distances up to 1.5miles, then you need to shop at a different store. That is some solid cushion. You're good as is with that directional and an omni. Apparently, i'm really good...i wonder if i should upgrade my antenna lol...

OH...and someone PLEASE check my math. these days i can screw up.
OK, here is the math on this...

Point2PointDist = 2 * ArcSin(Sqr((Sin((Lat1 - lat2) / 2)) ^ 2 + Cos(Lat1) * Cos(lat2) * (Sin((lon1 - lon2) / 2)) ^ 2)) * R

R = 6378.135 'Radius of the Earth in kilometers

Bearing = 360 - Deg(Atan2(Sin(lon1 - lon2) * Cos(lat2), Cos(Lat1) * Sin(lat2) - Sin(Lat1) * Cos(lat2) * Cos(lon1 - lon2)))

Make sure whatever computer you are using for your calculations that you change all or your latitude and longitude values to radians first...

Degrees * PI / 180

I am working out the up/down angle algorithm today and will post it later. This will get you started. i will write a little program that will simulate this graphically and post it as well. That way we can discuss additions and some advanced prediction calculations.
I haven't had a time to check your math too closely...but this is a problem people have solved before:


Isn't this the same problem an autopilot would face, knowing where it is and where a 3-D waypoint that it needs to go to is?
LOL...dude...i really have to find that thread...i did this problem already, same equation, although you did the bearing formula. all this as been surmised or done, on here, elsewhere. i'll look for it and post up the link.
Yes it is. Except you don't need to solve for 3D. Set your altitude and the aircraft will go there. The bearing calculation works but there is more to it. You also have to solve for line of position. This is the easy way to do it but it is better to use LOP so that the aircraft stays on the line between both waypoints. LOP helps solve the cross wind problem so the aircraft will not drift out of its lane and come into the waypoint from a direction other than the LOP.

I wrote that little software program. It works but as I mentioned, the antenna follows just behind the aircraft. i am solving that this evening. I am predicting the next place the aircraft will be by measuring the distance it travels between updates and calculating the next place it will be. Then, instead of moving the antenna to each update, I will keep the antenna in motion and use the updates as Information frames to keep the motion accurate. You will find at distance where the antenna pointer is really needed, the pointer moves very slowly. There were times with ours, if i wasn't watching the GCS, I would have thought the aircraft went down because the antenna just sat there for over a minute at times as we were in an orbit out about 6 miles.
I have a BASIC STAMP book that contains the code to control a Yaesu G-5500(?) Az/El antenna controller. I can dig it out if anyone is still interested in this discussion. I had considered making one a couple of years ago, and am interested in this project again.

My current thought is to use a 3axis Accelerometer to keep track of the antenna azimuth and elevation, with the 3rd axis maybe controlling polarization in the case of a yagi. This 3rd axis may not be necessary, but may be nice if you plant the whole setup on uneven ground. Given that the base station would be stationary, would accelerometers be sufficient? Since there would be no real centripetal forces to deal with, I am inclined to think they WOULD be, unless someone can explain to me otherwise.

Also considering coaxially mounted spotter scope with video capability to allow visual/motion tracking on laptop.

hello sir, I'm very much interested in ur project, can I get the detailed of ur project. thanx
I was considering this very same issue. I have seen tracking antennas that actively track an object by signal strength. This sounds like a great idea along with the dual GPS approach. I wonder if they can even be melded together for a whichever works best scenario.

I was planning to have the GPS on the UAV and a GPS on the antenna like you have mentioned.
I wanted to build an arduino based system with an electronic compass, GPS and gyros to calculate how much the motors actually turned the antenna.

Ideally it would be great if I could do it only with the electronic compass but I figured that would be used to align North and the gyros would be needed to make sure the that movement on all 3 axis would be accessible and fed back into the equation for adjustments.

I was planing on trying to calculate the path of the UAV and to account for turns and descents by basically calculating the turn rate and/or decent rates extrapolating the path if signal is lost temporarily.

Besides I have to figure out the tracking code so that I can track moving objects from the UAV. Stationary waypoints are a thing of the past. :^)

I like the dual antenna idea by the way.

If I ever get anything working I will try to post what my results are.
yeah similarly not totally i hv a project of tracking antenna of UAVs my first assignment is to choose which type of MOTOR is to choose or best for it to change the coordinates of the antenna while tracking it from the base station plz help me out
Nice job on the code, reading it right now. You did a good job on the math part BTW.

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