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happyelectron

Very Cool Tracking Antenna - Wow!

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I am copying this from a thread on the rcgroups website. Very Cool!!!

http://www.ltu.se/polopoly_fs/1.266...newformat-1.pdf

with a video of it working here:

The only thing I can’t figure out is they say the video receiver is circularly polarized, but they are using linear PC Yagi’s . So as usual I’m a little confused …

- Happy Electron

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Your first link is not working.

The video shows they have 4 aerials mounted at the focus of the dish so it knows if to go up,down,left or right. It's similar to one I drew up with four 15dbi patches, I got all the stuff but no time to build it <_<

Terry

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Very interesting demo video -- their project is very cool. Too bad the link to the white paper is broken.

I recall reading about it. From what I remember, the four tracking antennas feed individual preamps, followed by 2.4GHz band filters and broadband RF power detection IC's. It would be interesting to see what happens if a fellow showed up with WiFi router or a Spectrum R/C system and turned it on. :)

The only thing I can't figure out is they say the video receiver is circularly polarized, but they are using linear PC Yagi's .

I believe that there are five antennas on the dish system. Four for the tracking computer, and one for the video link. It is hard to tell from the video, but perhaps the video link antenna is circular polarized.

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I think this is the white paper to the project: http://www.eganfamily.id.au/archive30nov20...enveyAIAC12.pdf

The UAV's Tx is 10mW with a circularly polarized patch antenna. The base station uses linear polarized Yagi aerials (PCB based designs).

Correction: They don't have preamps after the antennas (that is a surprise). Just raw RF from the aerials feeds into the 2.4Ghz filters and RF power sense IC's.

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I think this is the white paper to the project: http://www.eganfamily.id.au/archive30nov20...enveyAIAC12.pdf

The UAV's Tx is 10mW with a circularly polarized patch antenna. The base station uses linear polarized Yagi aerials (PCB based designs).

Correction: They don't have preamps after the antennas (that is a surprise). Just raw RF from the aerials feeds into the 2.4Ghz filters and RF power sense IC's.

Sorry for the bad link, and Mr. RC-Cam, thanks for correcting it!

I was wondering how they were getting the "circular" in the system. It makes sense to put a circular patch on the plane so that the linear tracking Yagi's always have something to pick up. However, the only thing I don't like about a circular transmit patch on the plane is that it is pretty directional.

Otherwise, this is definitely one of the better set-ups that I've seen.

Terry, that's a cool idea to do it with 4 patches. Were you going to physically align the four tracking patch's so that they were off axis from a center recieve patch? That seems like a really interesting way to make a tracking antenna without having to use exotic pc yagi's aligned carefully at the dish focus. It may even be possible to do something like that with Helicals so that the tracking antenna system could be completely circular. That way a circular transmit antenna wouldn't need to be mounted on the plane.

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Were you going to physically align the four tracking patch's so that they were off axis from a center recieve patch?

Yes apart from no center patch, I was/am going to use the electronics from my 4 way diversity system to switch to the best patch.

It may even be possible to do something like that with Helicals so that the tracking antenna system could be completely circular. That way a circular transmit antenna wouldn't need to be mounted on the plane.

Yes that is a good idea. The down side to helicals is that they are only half the gain and are more untidy to transport than a flat panel. The plus side is they would give a much more steady signal that would make tracking easier.

The main problem with a system like this is what it dose when the signal is lost ?

When a 4 way static system looses signal it is still perfectly placed to regain the signal. When a tracking aerial looses signal it may point in the wrong direction and never regain the signal. Some of my early tests did this, it's very frustrating to see the aerial jittering about looking the wrong way :o

Terry

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Terry,

after reading literally hundreds of posts about tracking antennas I came to the conclusion that your 4-way tracking system is the most reliable/elegant solution for real life use.

Long range performance could be further improved maybe if combined with a very high gain helical (aka physically long) antenna on an azimuth-elevation motorized mount, controlled via GPS feedback. Combining the signals from these two systems through an Oracle diversity board could provide reliable signal under almost all circumstances and more chances for an early recovery in case of signal loss.

Dimitris

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Yes apart from no center patch, I was/am going to use the electronics from my 4 way diversity system to switch to the best patch.

The problem with the unpointed antenna approach is that it is hard to get the kind of gain one could get with a well pointed dish antenna (or even patch).

I've heard about using a GPS to point the tracking antenna, however, I like the idea of also using the signal strength information like these guys have. Also, I agree that a dish or helical is a real hassle to transport. So maybe a tracking patch setup with 5 patches would have some benefit.

Anyway, it is neat to see a tracking system work so well.

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So maybe a tracking patch setup with 5 patches would have some benefit.

I see no need for 5. With 4 patches mounted at 20deg to each other the target will allways be well within the max beam. Also you asume the center patch will always be perfectly on target but it will often lag behind the target when tracking fast. By using 4 patches in diversity mode it will give a more reliable signal as the beam is effectively wider.

Terry

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So Terry...

you have already built a RSSI based tracking antenna and a four patch static diversity system. Any thoughts about combining these two systems together and building the ultimate tracker??? ;)

Dimitris

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you have already built a RSSI based tracking antenna and a four patch static diversity system. Any thoughts about combining these two systems together and building the ultimate tracker???

YES! that is what I ment when I said :

The video shows they have 4 aerials mounted at the focus of the dish so it knows if to go up,down,left or right. It's similar to one I drew up with four 15dbi patches, I got all the stuff but no time to build it

It would also be bigger than what I use now which is a problem as I have to carry all my gear over the field on my own.

I may do it in the summer but I'm put off by the amount of wifi interference on 2.4Ghz, looking at my laptop it has found 9 networks in range :(

Terry

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You can always build it now and use it later for another frequency! :)

Apropos, did you find any RXs at 900Mhz or 1.3Ghz that ouput a usable RSSI signal in the sardine can?

Dimitris

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You can always build it now and use it later for another frequency!

Not practical realy, the 4 patches and 4 receivers are a big part of the design, if I change to another frequency they would have to be replaced at a large cost.

Terry

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Terry, I'd love to see you continuing your project :-)

I have the same problems with WiFi noise and others. Maybe selecting the frequency to a channel that doesn't interfere too much, could help. Especially RSSI is sensitive to everything on the same channel.

This is a channel table of WiFi frequs: http://www.moonblinkwifi.com/2point4freq.cfm

So running the video link on 2370, 2390, 2490, 2510 MHz should be worth a try.

I didn't have a chance yet to test it, but as soon as I have some results I will post them.

Edited by Hartwig

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So running the video link on 2370, 2390, 2490, 2510 MHz should be worth a try.

All those are illegal however. I haven't checked what they were assigned to, but it might also be an interference source...

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Also none of my receivers or transmitters works on those frequencies.

Terry

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All those are illegal however. I haven't checked what they were assigned to, but it might also be an interference source...

Yeah, good point! I haven't used them, yet. Do you have a link to a good information source on this that you can give me?

I guess 2490MHz should be within legal limits. I was looking for good information pages on it but all I found was the information that 2.4-2.5GHz ISM is usable for video transmission. Is that correct?

The highest WLAN center freq (chnl14) is at 2483.5MHz, so 2490 should have the least interference problems of all channels in the 2.4-2.5GHz range.

-AT-Terry:

I was talking about the systems from rangevideo, channels 5-8. I'm currently using airwave systems at 2410MHz which works very nice, but I "share" the freq with lots of others.

So, after all, a tracking antenna seems to me a good solution in terms of "filtering" what's in the air because it "listens" into the right direction. It only needs a reliable repositioning control. I would consider a GPS downlink via a seperate TX on 433MHz or whatever, and a GPS at the ground station to calculate azimuth and elevation.

Edited by Hartwig

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So, after all, a tracking antenna seems to me a good solution in terms of "filtering" what's in the air because it "listens" into the right direction.

Indeed, that is my main reason for going in this direction. It is a bit like walking a tight rope though, a great veiw but one slip and it a disaster.

It's still on my list of things to build but just not at the top. ;) After all I have the parts now anyway.

Terry

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I guess 2490MHz should be within legal limits

I might be wrong, but I thought that all throughout Europe the band ended at 2483.5, and at least here channel 14 is not available on WLAN equipment. There might be differences between individual countries...

Edited by Kilrah

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I wish I could build a GPS based antenna tracker w/ patches. Sadly, I don't have enough brain cells to figure out how to implement such a project. :( Should the antenna be driven with servos or stepper motors? What pic should be used to calculate the azimuth ascension based on the GPS coordinates of the plane vs. the reciever? Would it be better to use multiple diversity recievers and have all the patches fixed? I would imagine 8 patches in an octagon shape pointed at the horizon and another 8 patches above them at 45 degree angle would suffice, but that is getting very pricey. I have been interested in this since I saw cyber-flyer's system many years ago. What I would give to be that ingenious!

-dave

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You can always build it now and use it later for another frequency! :)

Apropos, did you find any RXs at 900Mhz or 1.3Ghz that ouput a usable RSSI signal in the sardine can?

Dimitris

Yes, 900MHz and 1.3GHz receivers have RSSI pin.

Best,

Vova Reznik

RangeVideo

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post-1954-1201706919_thumb.jpg

Edited by reznikvova

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