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Old Jan 19, 2010, 09:51 AM
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I think I just worked out a four-input design on paper as well. I'm just missing the balance tuning for RSSI, for which I'd like to see your methodology. I found that once you're comparing four inputs, it's easy to put out digital "pan" and "tilt" signals, which a generic pan/tilt servo system could apply. In addition, with a final two-channel switch, the mono audio (black rca plugs) gets switched as well.
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Old Jan 19, 2010, 03:43 PM
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I'm not sure i understand
HariEdo, are you planing about making an antenna tracket....based on Rssi?
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Old Jan 19, 2010, 04:03 PM
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HariEdo, are you planing about making an antenna tracker....based on Rssi?
It's potentially possible. Way too early to see if it works well in practice. The 4-input diversity needs to figure out which RSSI is the best, so if you arrange your antennae in a natural up/left/right/down pattern, then you'll get "left is better than right" and "up is better than down" signals, which can go to a tracking controller.

Unfortunately, 900MHz directional antennae are large and bulky and not very cheap to go buying four systems to feed this thing, and the motors to haul the array would be beefy as well.
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Old Jan 19, 2010, 04:57 PM
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I got the idea from your circuit, HairEdo. You for some reason sent out the RSSI to a video switcher as well. If you build two of my diversity controllers and then send their outputs to a third channel diversity controller with the RSSI's of the winners such as in your design, then you now have a 4 input device. Each signal must pass through 2 switches, though. It will certainly work. I will make a block diagram for it later.

Right now I have a plane to fix. The transmitter ripped off the airplane in flight while I was on the maiden flight! I was able to get the coordinates from my OSD and found the airplane 150 feet away. No VTx, though I had to order another one. I will post the video, though as I had several channel switches on my diversity before the VTx fell off.

-Alex
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Old Jan 19, 2010, 07:33 PM
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Originally Posted by IBCrazy View Post
I got the idea from your circuit, HariEdo. You for some reason sent out the RSSI to a video switcher as well. If you build two of my diversity controllers and then send their outputs to a third channel diversity controller with the RSSI's of the winners such as in your design, then you now have a 4 input device.
"For some reason" like posts #31 #32 #33 in this thread. It was my intention to put the winning RSSI out for this purpose. But like you, I aim to make a one-board 4x version, with all comparators together.
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Old Jan 20, 2010, 01:51 AM
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Why not build a "pyramid" made of four 8dB standard patches?
They have 90 degrees coverage, so will close the circle pretty nice ? No more tracking mechanics complications.
The idea is not mine, was issued first time by a guy Dimitris76, or in one of his threads, as a "mushroom" antenna approach. But the term "pyramid" is mine, patented already
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Old Jan 20, 2010, 03:12 AM
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90' conus on 8db patches? You sure?
I always thought it was more along the lines of 45' ?
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Old Jan 20, 2010, 05:17 AM
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You may be right, the one I use is 60' at -3dB
http://worldnet.ro/detail.php?id_pro...ory=14&lang=en
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Old Jan 20, 2010, 05:34 AM
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Originally Posted by RENATOA View Post
Why not build a "pyramid" made of four 8dB standard patches?
They have 90 degrees coverage, so will close the circle pretty nice ? No more tracking mechanics complications.
The idea is not mine, was issued first time by a guy Dimitris76, or in one of his threads, as a "mushroom" antenna approach. But the term "pyramid" is mine, patented already
Thats exactly the point of having a multi chanel diversity, not tracking required, reduced possiblility of mecanical failure...ect...no osd dependency
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Old Jan 20, 2010, 07:12 AM
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For multiple antenna using static RSSI Xversity, Don't forget, there may be other sources of RF around.
i.e. say pick up signal from another source that is stronger and different direction, I would expect your video would then switch to that antenna - possibly losing your video from the plane totally until antenna switched back.

Downside of vs the GPS tracker.

Picking good receiver location and strong video signal would minimise impact. And using measuring video frame quality would improve further if that's a feature of designs.

Would like to see how well it works in real world testing though. Always wondered what it would be like.
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Old Jan 20, 2010, 09:29 AM
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Shikra, this is exaclty the reason you need to test the base station BEFORE turning on your Tx. It is also the reaon I only use a two channel. A 3 channel with three directional antennas is perhaps the best over all.

A good set up would be three 8 db patches. Two on the outside mounted 60-75 degrees apart and then one in the middle turned 90 degrees for better reception when banking. This gives you nearly 180 degrees of coverage and will keep a strong signal in a bank.

With the two channel unit, I place my antennas 60 degrees apart in the same polarization. However if going for distance in a moderately straight line, I suggest two patches aimed in the same direction 90 degrees rotated from one another.

-Alex
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Old Jan 20, 2010, 09:32 AM
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Don't forget you can always turn your base station manually to get more coverage. Your foot is much more reliable as an antenna tracker than sny electircal drive, just maybe not as accurate... but that's what the diversity is for

-Alex
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Old Jan 20, 2010, 11:33 AM
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Shikra, this is exaclty the reason you need to test the base station BEFORE turning on your Tx.
-Alex
Agreed - always do that. And pick take-off points carefully to minimise further.

Biggest issue I experience is if someone drives by and stops to see what I'm up to - pick up bluetooth / wifi or ignition iterference. That has been my single biggest problem.

Now I think about it, I can't remeber the last time I needed to change. If I see interference on one I usually find it on the others too.

Anyway - interested in this and range you guys get. I like the idea for near range to maximise quality.
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Old Jan 20, 2010, 12:26 PM
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Shikra, I never considered somebody with a blue tooth or WiFi showing up. That's a good point. opne of the many reasons to stay out of the 2.4 GHz band unless you are in the middle of nowhere.

The best way to test the base station is simply to turn it on and rotate it back and forth over the area you intend to fly and see if your diversity LEDs switch at any one particular point.

I don't know if this will increase range (perhaps some if you use oppositely polarized antennas), but it sure increases your area. It nearly doubled my flying area. I have no desire to go out more than 1.5 miles, which is the end of my Tx anyway. However I do like to fly around all over the place.

-Alex
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Old Jan 22, 2010, 08:31 AM
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I've gotten my Digikey box of parts. Still waiting on a Sparkfun box that may arrive today, and the first PCBs will take another couple weeks. I've already made improvements in my design files for a "revision 2" with more RSSI inputs, better indicators, smaller power components, etc. Will update with the horror stories (or successes) as things progress.
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