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Terry

Auto Tracking Aerial

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For sure I could do it that way as it is the the most comon solution for most of us but I would like to explore an alternative, who knows where it may lead if it works !

Terry

UK

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I'm with Terry.

I think gps feedback is "cheating". It has advantages. However, it it threoretically not a robust system. It is potentially a "moment 22" system.

A radar does not have to get position data from the objects it is supposed to track. If it was, it would of cource be redicoulous from a military point of view.

Extremely light model aricrafts, or other model aircrafts wich you might not want to put a GPS recevier in, can not be tracked by a system relying on GPS feedback.

Best Regards,

Bosse

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I'd be happy with a proggie to run the directional antenna servos for now-is there one out there? The antenna tracking stuff is way out of my league.

Im thinking about setting up an on-board failsafe something like this...if the signal is lost the plane returns to level/upgright attitude for 10 seconds to 'wait' for groundsation signal, if signal is not recovered in 10 seconds the autopilot RTB failsafe is activated.

groundstation can recover plane signal by calculating last known heading/speed & altitude and intersecting flight path, if no connection recovered then plane is autopiloted back Any thoughts?

Extremely light model aricrafts, or other model aircrafts wich you might not want to put a GPS recevier in, can not be tracked by a system relying on GPS feedback.

If you don't have on-board gps what's the point of flying BVR?

Edited by rpv

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If you don't have on-board gps what's the point of flying BVR?

Sorry I dont see your point ?

Can you explane the conection between flying BVR and GPS , thanks.

Terry

UK

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:unsure:

A while ago, I was reading on a solar tracking system, using 4 solar panels to track the sun, while moving the larger main panel. The 4 panels were hooked up to standard electric motors(one for each axis) and basically the panel (x and y sets) with the most juice won and moved the unit until both sides (x or y) were at equal strengths.

Just a passing thought.

Mr Boulevard

Edited by mr boulevard

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Yep. if you look at the first post you will see that is more or less the idea I started with !

Terry

UK

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OK, time has passed and I am ready to start putting something together !

I have spent a lot of time optimising a new patch for use on the UK 2.4 frequencys after finding out that the old stuff I made using plans from the web were not as good as I thought (thanks to buying a reflectometer). I also did some testing on feeding the patch with a feed horn and found it out performed my helical by a mile. So now its time to start building the auto tracking bit and I need some pointers. I need a rotating system, can anyone point me to some good close ups of the mechanics on such a system ? I dont mind if it is DC or stepper motor, I just need a nudge in the right direction with the gearing and stuff.

Terry

UK

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Hi Terry,

I have used systems like you are describing several times over the years to solve a number of tricky signal detection problems. I have frequently heard it referred to "phase demodulation." This type of simple scheme has the uncanny ability to pull extremely small signals of interest out of a very noisy environment with great success. Applied to your situation, I suggest that you consider using two model airplane servos. One would dither the antenna back and forth over a narrow number of degrees. The second servo rotates the antenna (and the first servo) over a wide range of rotation. The principals and circuitry are fairly simple:

The first servo is alternately sent pulse trains of two different pulse widths. The antenna dithers back and forth a few degrees in response. The dwell time at each dither point is a good bit longer than the time it takes to transit the two directions. The RSSI voltage is examined alternately as well. The RSSI voltage magnitude read during the first dwell time is compared with that of the second dwell time.

The difference in voltage drives an integrator in one direction or the other. The absolute magnitude of the integrator voltage lengthens or shortens the pulse width fed to the second servo and thus controls the rate and direction of antenna rotation. Only when both voltages are the same amplitude will the antenna stop rotation. The system has thus homed in. Because the system can be made so sensitive to very small voltage differences, there is just about no sensitivity penalty due to beam width issues because the dither angle may be made extremely small. Thus, you should not need a second antenna.

The circuitry can be accomplished with standard “hard-wired” electronic parts and need not contain a microcontroller (although a microcontroller can be used to perform many of the required functions).

T.I.

Edited by Temporary Insanity

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Well T.I, inspired by your last post I got on with the job and made a simple auto tracking/searching patch. I dont know what I was worried about, it works like a dream ! My system dose as you described but I am just using 1 motor and no servo. Its great when you lose the picture as the aerial still picks up the weak signal and is pointing in the right direction for when it gets strong enough to to bring the picture back. Much beter than a helper waving the aerial about in hope of finding something !

post-6-1089925900_thumb.jpg

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I will do my best but I dont know how to post it ! I will give it a go after the weekend as I am about to leave for the RIAT at Fairford.

Terry

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I shot some video of it but I dont seem to be able to get my web space to work properly, is there anywhere I can upload it to ?

Terry

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I have had some interest via PM's on helping others with thier systems. I am more than happy to do this and will work on the program to get the best from it over the next few weeks and will supply a PIC to anyone that wants one. The only point is that you need to build your hardware so I know your sweep speed and RSSI threshold and which way it goes (I may make the threshold self calculating),also the type of aerial would be handy to know.

Terry

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Im using pinnacle 8 so I can make it any size, Im not sure of the best settings to use but I have tried a few and the smallest size is about 7mb. I can edit it if needed !

Terry

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T.I, you may be able to pick up a file that big but I cant send it !

Could try messenger , do you know the max file size that can be sent with that ?

Terry

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Hi Terry,

There's no maximum file size for MSN Messenger file transfers, but it is alot slower than other methods. 7-8mb is going to be about 10 mins to transfer.

Hope this helps

Gavin

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Hi Terry,

While we sort out this video thing, let's keep the conversation going.

I was wondering how much voltage resolution your system has. I'm also wondering how many degrees you are dithering. Can you say?

Meantime, I'm also interested in building a similar system and would be interested in getting a chip or anything else you are willing to share.

Best,

T.I.

Edited by Temporary Insanity

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Sorry Guys, Ive been away a couple of days. No secrets here its all very simple stuff. Im just feeding the RSSI into the pic with no buffer, so the res is not great but it dose not need to be ! In practice this just has not show itself as a problem. You could add an op-amp buffer but I will not do this unless there is a need. I will try and sort out a vid as it is much clearer than writing it out but for now....

The basic operation is that it will remain still for 5 sec then look right 30deg, if the signal is stronger it will stay there for 5 sec then repeat...if the signal is weaker it will return and stay still 5 sec then look 30deg left,if the signal is stronger it will stay there for 5 sec.....and so on ! The 30deg and the 5 sec delay are set for the aerial/aircraft needs and can be changed with little problem, I use the 5 sec delay as I dont need a very fast track rate with my plane/range. I use the 30deg as any less and with the wide beam patch I use it just slows the track rate for nothing. Oh, and if the signal is lost it will just rotate right until it is found then stop and look for the strongest signal.

PS. my e-mail address is now correct ! sorry Guys :o(

Terry

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