Posted by Scott James on September 20, 2008 at 12:24am
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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Hello. Yesterday i thinking about this problematics. My friend need tracking UAV because he have on UAV video transmitter on 5.8GHz. For good video signal, receiver antenna needs to be directed to transmitter antenna. My version of the solution of this problem is: On airplane is the GPS and RF GFSK modem module. RF modem module have omni-directional antenna and high output power. Frequency of the RF modem is around 430MHz. RF modem transmit the GPS data. Antenna ground tracking device have RF GFSK modem too, with omni directional antenna also (or one-direction antenna with wider angle then antenna for video receiver). For tracking you need to know only two angles: one is azimut second is latitude angle. You dont need to know distance from you to UAV. I attached the picture of the problem. On picture needed angles is gammaN and gammaH. From GPS data you can know the alfaA, bettaA, alfaL, bettaL angles. Also from GPS data you can know latitude (h). It is enough for rating needed angles. Before start you just to must calibrate ground antenna station. Software of the antenna tracking device need to know coordinates of the ground antenna placement. You just need to place UAV GPS-FSK modem traking module on ground antenna station and let software set this coordinates like ground antenna station coordinates. Then you need to turn ground antennas exactly to north and set this position like default. So now you can fly with UAV. Tracking device will rate azimut and latitude angles from GPS data and turn antenna exactly to UAV. So this is my idea.
P.S. Maybe the math problematic can be more simple. Amateur UAV will not fly on hundreeds kilometers. So i think that is possible transfer spherical tracking problematic onto plane tracking problematic. The rate code will be more simple and faster.
P.S.2 Sorry for my english.
Could the groundstation Xbee which is receiving telemetry from the UAV be used to point a tracking antenna? Maybe an additional arduino board could take in telemetry from the GS xbee and then send out ftdi to laptop for groundstation software and also use outputs to drive servos?
Also, the RTL variable could be used if you launch from where your antenna is. No need for a GPS on the ground? or even program in your starting coords before flying?
There's a company in Holland, Immersion RC that makes FPV gear. They are about to release a full antenna tracking solution.
Here's the RCGroups thread. Apparently, they are demo-ing their units at an PFV meeting in France over the next couple of days. http://www.rcgroups.com/forums/showthread.php?t=959889
I'm glad people with the technical knowledge are pursuing this. Fantastic work.
From my limited code trading skills i take it that you planning to use Xbee modems to transmit the NMEA data back to the ground and also use standard servos for 180 degrees of movement. Is this correct?
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
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.
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.
Thoughts?
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we talked about this in another post...ummm...i will try to find it and send you the link. I am going to attempt to do this.
I think, wtih all the things that you are putting in, you are forgetting that a directional antenna has a cone for the transmission and recieving (Tx/Rx), not just point to point. I picked up an antenna with 110*y and 30-40deg*x. This means that as long as the base of the cone is on the horizon, i don't have to worry about an entire axis of rotation.
Another method is that you have two antennas, an omni for near-by transmissions, and a directional for when it gets far. that way, when you have to do the derivaties for the the airspeed relationship, you don't have wild movements and the (TxRx) cone covers a wide area.
In fact, that is the method i will be using lol. It just makes life easier.
We did this with a Yaesu antenna pointer. It had an analog output (1 to 5v I think). Anyway, We built a little basicstamp board with a A/D on it. This gave is a reading from 0 to 255 (8 bit... a little lack of forthought there). However it wasnt that bad because even if I used a dish it was well within the 5 degree beamwidth of the antenna. We were using a Yagi so we were well within the tolerances. It was a fixed location antenna so we knew where we were. The "UAV" was actually a cessna tu-162 with a 10 watt 2.4 ghz analog video transmitter and a 900mhz datamodem. Even in a basic stamp with a co-processor we were able to capture the telemetry stream with GPS coordinates and have the antenna follow the aircraft flawlessly. I even wrote in an prediction algorithm to keep the antenna pointed right at the aircraft instead of slightly behind it. The tracker had both pan and tilt and the math isn't that hard.
Also a little side point..Forget using long antenna lines too. Use a 6 inch peice of coax and put the receiver right at the antenna. run your line level stuff off the tower or tripod. This will really,really make a difference!
Replies
Hello there. i am abid hussain from pakistan. can i learn something about UAV antenna tracking system from you.
thanks
P.S. Maybe the math problematic can be more simple. Amateur UAV will not fly on hundreeds kilometers. So i think that is possible transfer spherical tracking problematic onto plane tracking problematic. The rate code will be more simple and faster.
P.S.2 Sorry for my english.
smerovanie antenn.PNG
Also, the RTL variable could be used if you launch from where your antenna is. No need for a GPS on the ground? or even program in your starting coords before flying?
Anyone think this is doable?
Here's the RCGroups thread. Apparently, they are demo-ing their units at an PFV meeting in France over the next couple of days.
http://www.rcgroups.com/forums/showthread.php?t=959889
From my limited code trading skills i take it that you planning to use Xbee modems to transmit the NMEA data back to the ground and also use standard servos for 180 degrees of movement. Is this correct?
Thanks,
Nick
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.
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.
Thoughts?
I think, wtih all the things that you are putting in, you are forgetting that a directional antenna has a cone for the transmission and recieving (Tx/Rx), not just point to point. I picked up an antenna with 110*y and 30-40deg*x. This means that as long as the base of the cone is on the horizon, i don't have to worry about an entire axis of rotation.
Another method is that you have two antennas, an omni for near-by transmissions, and a directional for when it gets far. that way, when you have to do the derivaties for the the airspeed relationship, you don't have wild movements and the (TxRx) cone covers a wide area.
In fact, that is the method i will be using lol. It just makes life easier.
Also a little side point..Forget using long antenna lines too. Use a 6 inch peice of coax and put the receiver right at the antenna. run your line level stuff off the tower or tripod. This will really,really make a difference!
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