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Old Aug 31, 2009, 07:22 PM
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CATPart's Tracking Antenna

I thought I would show you guys my new Tracking Antenna Base assembly. I am still waiting on parts and I need to finish modifying my plane but the Base assembly is ready to go. Oh yea, those are cardboard "simulated" antennas, still waiting for those to arrive also.

This runs off some custom software I developed which is full featured and robust. Its pretty interesting, and I am still working out some bugs, and have yet to field test. So far it works great in simulation.

CATPart's Tracking Antenna for UAV and FPV (0 min 43 sec)
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Old Aug 31, 2009, 07:53 PM
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Wow impressive!

it do not look amateur
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Old Aug 31, 2009, 08:30 PM
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Perth, Western Australia
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Thanks for sharing.
A couple of questions: Are you using servos or stepper motors? How many degrees of travel does the pan axis have?
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Old Aug 31, 2009, 08:35 PM
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Will it be finished before the Mother ship arrives?
Great job, keep the progress updates and pictures coming.
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Old Aug 31, 2009, 09:04 PM
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What data are you using to do the tracking?
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Old Aug 31, 2009, 09:20 PM
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Thanks guys.

Martin I am using NMEA $GPGGA strings for now. I could modify the software to read any data.

Nick I am using custom servos, but any servos could be used with my software and controler. My tracker has 360° pan and 135° tilt.
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Old Aug 31, 2009, 11:23 PM
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Quote:
Originally Posted by CATPart
Thanks guys.

Martin I am using NMEA $GPGGA strings for now. I could modify the software to read any data.
Sorry is data transmitted down or read off an osd signal using audio/VBI?

I must say it is great looking. Looks like's a radio telescope setup.
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Old Sep 01, 2009, 07:45 AM
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This is quite a promissing setup. One question though. Is the distance between the antennas adjustable? As you know - and it has been covered many times in this forum the distance between the center of the antennas really can affect the reception quality....
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Old Sep 01, 2009, 08:01 AM
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Uhm, few things, you need to mount it higher up off the ground, unless you plan to be flying at high altitudes all the time. Also the distance between antennas needs to be a value that's not a multiple of the wavelength of the RF frequency used. Oh, and you need to install a couple of .50 caliber machine guns to the sides

Cheers,

Sander.
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Old Sep 01, 2009, 09:12 AM
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Quote:
Originally Posted by ssassen
Also the distance between antennas needs to be a value that's not a multiple of the wavelength of the RF frequency used.
Sander.
How does this rule hold up if you are receiving on two frequencies (say 900Mhz and 2.4Ghz.)
Thanks,
Nick
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Old Sep 01, 2009, 09:26 AM
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Nick,

Quote:
How does this rule hold up if you are receiving on two frequencies (say 900Mhz and 2.4Ghz.)
Well, the idea of a spacial diversity system such as this is that if due to reflections of the incoming RF signal off of (nearby) objects it could happen that on one antenna the actual signal and its reflection with a 180-degree difference in phase cancel each other out (1 + (-1) = 0), causing for a deep null.

To counter this we use two antennas of similar polarity that are spaced out at a distance not equal to an integer of the wave length of the RF signal frequency used. Statistically we can now prove that if one antenna suffers from such a deep null due to multipathing the other in the vast majority of cases won't, hence will receive a good RF signal.

If you use two antennas on different frequencies you factually don't have a spacial diversity setup, and you won't have any of the benefits of spacial diversity. If due to multipathing one of the antennas suffers a deep null the other could be as well, although the likelihood of that happening at the same time with two different RF frequencies is very small.

Having said that, why would you want two Txs at different frequencies on a plane? Better pick one that suits your needs best at your location and use a good spacial or polarity diversity antenna setup.

I hope this answers your question? If not, keep asking, I don't mind explaining.

Cheers,

Sander.
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Old Sep 01, 2009, 09:40 AM
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Now that's too cool you CAD junkie!!
Quote:
Originally Posted by CATPart
I thought I would show you guys my new Tracking Antenna Base assembly. I am still waiting on parts and I need to finish modifying my plane but the Base assembly is ready to go. Oh yea, those are cardboard "simulated" antennas, still waiting for those to arrive also.

This runs off some custom software I developed which is full featured and robust. Its pretty interesting, and I am still working out some bugs, and have yet to field test. So far it works great in simulation.

http://vimeo.com/6369680
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Old Sep 01, 2009, 10:59 AM
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This is not a diversity setup, though I considered adding a diversity omni for close in flying. One antenna is for 2.4 gHz video and the other is for 900mHz telemetry data...(I don't own an OSD telemetry system, and higher end autopilot (atto) people may like a setup like this) I have been wondering if the proximity between these two antennas would be a problem or not. I figured I would just test and see. Do you think it will work Sander? I can adjust the spacing, but it will start getting pretty wide. Those antennas are each 16" square. My gut tells me it will work fine like this. Height off the ground I think is fine, since I always just put my patch antennas on the ground an it works great. But I can always change the legs if necessary. It can be taken apart and reassembled rather easily.

Machine gun? I have been contacted by the military about adding a 50 cal, joking
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Old Sep 01, 2009, 11:03 AM
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CATpart,

If you use different frequencies I wouldn't worry, they're spaced far enough apart in that case. The height off the ground becomes an issue if you fly further out, the antennas will be pointed at the grass if you're >1 mile out, which does really attenuate the signal quite a bit. I normally raise them to at least 6 to 8 feet about ground level.

Cheers,

Sander.
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Old Sep 01, 2009, 11:25 AM
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Quote:
Having said that, why would you want two Txs at different frequencies on a plane?
3 words: Full Carbon Glider
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