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This may seem like a daft question but...why dose a diversity receiver work ?

Dont say its because when one aerial looses the signal the other one takes over. If your plane is high in the sky and on the ground you have 2 aerials only 6" apart why should you get a signal on one and not the other ?

Terry

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Spatial diversity antennas are very interesting. They work because microwave wavelengths are extremely short and directional.

At 2.4Ghz, six inches is more than one wavelength distance. That is like having two 27Mhz CB radio antennas 44 feet apart. And, since the two received signals will often be out of phase, if one is harmed by multipathing, then the other will probably remain intact.

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So the answer is multipathing, I would have thought with the tx in the air and the rx in the middle of a field that this was not likely to happen ?

I dont get dropouts very often but sometimes when I fly near to my max range and banking I loose signal for a second, do you think diversity would help in this case ?

Terry

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Terry

Please go to

http://www.klarichelectronics.com/kedrx-2401.htm

and take a look at the demo video of Matt Klarich's Diversity Receiver,

Matt worked here at AUAV at the time that he developed the first prototype.

I have to say that the prototype was outstanding and his new versions are even better.

Just so you know I don't receive any compensation for promoting Matt's product other than knowing that it will do the job for you.

Dave Jones

AUAV.net

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I don't see how it could improve range in the case you mention. As the signal is blocked at the source by the plane, there is no reason that an antenna a few inches further would pick the signal better. When I'm flying close to the range limit moving the antenna won't help in that situation.

In a clear field, where I also usually fly, I don't think there will be a real benefit. The interesting point for me would be to use one omni antenna so you are safe and have good coverage at short distance, and one higher gain one that you'll point in the direction you're likely to be flying.

I'm always heseitating between the omni and the 8dBi patch on the field, this would certainly solve that problem.

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Terry - your question is absolutely valid. I believe that Matt's receiver will be losing video signal as well as any other non-diversity receiver when model's airframe is blocking the transmission. That's the reason why I always used two independent transmitters on different parts of the aircraft. If one will be blocked the other will continue to transmit. My diversity receiver selects signals from two different receivers that are working on different bands. It is not difficult to modify Matt's receiver to do that. But for some reason many people are missing the point.

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Thanks for your input guys, this is the only place you can get this kind of info, nobody else has the experiance !

I know what you mean Kilrah, the patch would work well until you come back to land and then you fly behind it. That was why I made my simple auto tracking patch, it always points in the general direction of the plane which is good enough for a simple patch.

I think cyber-flyer has the best idea in using more that 1 transmitter but its doubles the power and weight requirment.

Maybe lowering the aerial on an arm after take off would work, sort of retractable undercart in reverse...

Terry

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Hmm, actually I did try something new last sunday and again today, which is a little bit related to the tracking antenna...

The point wasn't there at all, but more that we now have snow here :(

Actually that's really amazing, in the past we would only have some for a couple of days a year, and now since last winter it seems not only to last but also to come very early! :o

So as I was always putting quite a lot of stuff on the ground (PC, receiver and... myself) I had to find a new idea...

I simply take the same ones but I start the recording and then put everything in my backpack. I stand up during all the flight, using the neck strap to hold my heavy 9Z that I usually have on my knees.

I put the 8dBi panel on my shoulder facing 45° up and to the front, and so I can just turn to get the best reception ;)

Actually it's quite useful, as I flew today near the tall buildings in the area, and this time as I had quite a lot of multipath interference I could clearly see that the best position is not always facing the plane in that case...

The omni was quite bad, but the 8dBi panel pointed away from the buildings was the good solution.

BTW a lot of people had asked me if it was possible to fly FPV while standing without losing balance, I had never tried so couldn't tell them anything. Now I can answer YES :)

It's more difficult to know what way you are facing though... As you have no reference it goes like integration drift... you know you did turn a bit that way, then the other way... and don't remember anymore ;)

post-2-1133468052_thumb.jpg

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Sonds like it works !

I think if it was me I would use tripods and folding tables, sounds hard to sort out if a wire or something goes wrong.

I do find the auto tracking patch will sometimes point at a building but its not a problem as the picture is still good. Maybe I dont get ghosts as I use 10mW most times ? As soon as the signal drops below a preset level the aerial will rotate until it finds the signal again so the loss will only be 3 seconds max.

Terry

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One of the other ways that a diversity receiver can help your range is via polarization diversity.... assuming you have your two antennas oriented such that their polarization is 90 out of phase to each other.

The idea is that as the plane banks over, one antenna is going to become cross polarized (and effectively loose 20dbi gain) while the other antenna's polarization matches that of the plane.

This doesn't solve the issue of blocking the signal with the plane body though.

Regards,

Bill

http://www.blackwidowav.com/Diversity24.html

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Yes Bill, that is a good point, it is probably true to say that I get both problems together. Its not bad now but I cant help tinkering and trying to improve it further. I dont bank the aircraft more than 30deg so what would the loss be in this case ?

Perhaps 2 patches with 1 leaning right at 15deg and the other left at 15deg would be good using diversity ?

Terry

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That sounds like it would work, assuming polarization is the issue.

That's the cool thing with diversity reception... you have twice as many ideas to try out ;)

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Hi folks... Just want to let you know there's another comany shipping the diversity receiver if you're interested. Check out http://www.futurehobbies.com

In the interest of full disclosure, I am friends with the owner of this new site. I thought I'd post because it sounds like there's interest in this unit and I know Wade at Future Hobbies would be happy to answer questions about it.

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It looks like a "re-branded" BWAV diversity system (OEM arrangement). Is that correct?

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Sure looks like it too me, personally knowing pretty much exactly what is going into one of these units that price is kinda steep. Just MHO.

MK

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It looks like a "re-branded" BWAV diversity system (OEM arrangement). Is that correct?

My understanding is that BWAV and Future Hobbies are getting these from a 3rd party, but I could be mistaken. The price appears the same on both sites.

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Sorry, it looks like I was confused on who created the new diversity receiver. I thought Bill at BWAV, along with an outside electronic engr, were behind the latest version. I guess not. But, that doesn't really matter. I was mostly wondering if the these units were the same design, which it appears they are.

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Hi RC-CAM,

I can't speak for the future hobby unit, but you are correct about the BWAV unit being designed by myself and Ira over at Iftron Technologies.

Bill

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Yb2normal, looking at the Future unit, the front panel layout and the case are EXACTLY the same as yours. Just curious -- is it your system with essentially a different face plate?

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