IBCrazy's Cloverleaf circularly polarized antenna!

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Re: IBCrazy's Cloverleaf circularly polarized antenna!

Postby bmsweb » Sun Aug 21, 2011 8:10 pm

Allan Warner wrote:You may find these threads of interest:

Wow More reading to do :D Lucky my FPV hardware hasn't arrived yet . . . more time to do reading! Thanks for the links . . always an interesting read
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Re: IBCrazy's Cloverleaf circularly polarized antenna!

Postby kaptain_zero » Mon Aug 22, 2011 2:24 am

Thanks for the corrections on the db losses.... uhh.... what were they again?!?! :lol:

Regards

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Re: IBCrazy's Cloverleaf circularly polarized antenna!

Postby Oops » Thu Sep 22, 2011 8:21 am

Dumb question but I need to ask the experts: a standard whip can be mounted vertical up or vertical down I presume? I am thinking of mounting the 5.8GHz under the wing so the antenna will point down. At present the signal gets particular bad when I fly straight back to me. The antenna is mounted behind the wing on top of the phoenix 2000 fuselage (and behind the heatsink).

Also, the signal can be excellent one moment but bad the next despite no apparent changes in attitude. I do fly regular over a km away and even then the signal is usually good but then suddenly it gets snowy to clear up moments later. Would a clover improve any of this? Would mounting the whip under the wing and ~100mm away from the fuselage help? During landing it will fold back.

Finally, the 5.8GH signal gets very quickly attenuated by trees and the likes. My ideal spot is surrounded by high pine trees. I do have the receiver on a 4 meter pole (with the standard whip straight up) but that makes no difference in such situation. I presume a clover would be no improvement?

I am also waiting for Bruce to produce his switching antenna solution.
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Re: IBCrazy's Cloverleaf circularly polarized antenna!

Postby Sid Sideslip » Thu Sep 22, 2011 10:23 am

The signal may well be attenuated by shielding as the plane flies towards you, compared to flying away. As with trees, 5.8GHz is not good at traversing obstacles (from what I know so far, which ain't all that much).

As long as the antenna is mounted vertically (up or down) it will radiate the same vertically polarised pattern (assuming the plane is flying level).

As for distance flying, I'm guessing it's a combination of maybe any transient interference overwhelming the signal combined with similar transient multipathing or obstructions.

I can't comment on cloverleaf designs yet because I don't know enough.

One thing that puzzles me though is this. With a standard vertically polarised whip antenna and Rx station antenna, you lose a hell of a lot of gain when the plane banks, when the contact surface area (if I can use that term) of the two radiation patterns diminishes markedly. Why then don't we have an antenna on the model that uses servos to lean the antenna over so that it still aligns with the base station's antenna? I mean, it' seems obvious to me, and with modern electronics (GPS, accelerometers, or even a gyroscope, to get old fashioned) it should be easy to provide the instructions to the servos to know which way to lean the Tx antenna and by how much.

The plane banks, but the antenna remains vertical and so stays aligned with the Rx, polarisation wise (within limits, but we are talking the FPV here, not radio control of the flying surfaces)...so, no need for circular polarised set ups.

Or am I missing something here?
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Re: IBCrazy's Cloverleaf circularly polarized antenna!

Postby Allan Warner » Thu Sep 22, 2011 2:14 pm

Tx and Rx CP antenna (correct polarisation - both RH or LH, not mixed) will show a 3dB loss compared to a pair of correctly aligned linear polarised antenna. But, the main useful feature of CP is the very good rejection of multipath signals. So, tilting linear polarised antenna on the plane will not do anything for multipath problems. The higher the frequency the greater the problems from multipath signals ie 5.8gHz.
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Re: IBCrazy's Cloverleaf circularly polarized antenna!

Postby RCModelReviews » Thu Sep 22, 2011 7:03 pm

Multipathing tends to occur more at close ranges than distant ranges -- although it can still be an issue at distance.

Sid's idea is actually an interesting one -- perhaps worthy of some experimentation. Just create a dial-axis mount with two servos and throw any FY20 or FY30A (which I'm reviewing at present) on it.

One thing that *really* helps is a directional antenna for the video receiver. It'll not only give you a stronger signal but, because it looks down a narrower beam, any off-angle reflection is greatly attenuated when compared to the original signal.

I'm going to do some tests with directional antennas and 5.8GHz as soon as the weather allows.
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Re: IBCrazy's Cloverleaf circularly polarized antenna!

Postby Sid Sideslip » Thu Sep 22, 2011 9:21 pm

RCModelReviews wrote:Sid's idea is actually an interesting one -- perhaps worthy of some experimentation. Just create a dual-axis mount with two servos and throw any FY20 or FY30A (which I'm reviewing at present) on it.

One thing that *really* helps is a directional antenna for the video receiver. It'll not only give you a stronger signal but, because it looks down a narrower beam, any off-angle reflection is greatly attenuated when compared to the original signal.

I'm going to do some tests with directional antennas and 5.8GHz as soon as the weather allows.


I just looked up the size and cost of the FY20 and it's not only small, but also around $100, which is affordable. I will give my idea a go, maybe on the phoenix (more room to experiment). I'll use a HobbyKing camera pan-tilt head (covered by a suitable fairing) mounted so the camera board faces up, with the antenna screwed to the now horizontal board (i.e. imagine the camera below is the antenna). I'll rope in my bro in law to do the signal intensity measurements for me as he has all the gear at work. Should be fun.

Of course, if you want to give it a try Bruce, I'd be stoked, as you have the gear already, except may for maybe the pan-tilt head and they only cost a few dollars.

Image

If this proves worthwhile, which is should, especially at extreme range where misaligned antennas signal attenuation is most noticeable, then I want it to be known as a "Sideslip antenna". :lol:

BTW Bruce, can you buy auto tracking directional antennas? Seems to me that would be pretty easy to set up too.
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Re: IBCrazy's Cloverleaf circularly polarized antenna!

Postby Sid Sideslip » Thu Sep 22, 2011 9:40 pm

Added: Of course the pan-tilt head will have to be supported in the vertical plane, by an aluminium angle bracket and suitable bearing, so that that servo is not carrying all the load. Easy enough to do.
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Re: IBCrazy's Cloverleaf circularly polarized antenna!

Postby RCModelReviews » Fri Sep 23, 2011 4:50 am

I've been scoping out an auto-tracking antenna for longer-range FPV setups.

I plan to use the FrSky 2-way RC gear (which can transmit the GPS coordinates and altutide back to the ground-station that would then do some quick math to work out the correct bearing and azimuth to point the antennas.

By using a hi-gain 2.4GHz yagi (20dB) for the RC gear you'd get the same effect as running 6W of power from your RC transmitter and using a 13dB patch for the 5.8GHz video would effectively turn a 200mW video sender into a 4W one -- in terms of signal strength.

That combination ought to be good for at least 20Kms or so -- albeit line-of-sight rules still apply (in fact more-so)
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Re: IBCrazy's Cloverleaf circularly polarized antenna!

Postby Sid Sideslip » Fri Sep 23, 2011 4:57 am

Sounds awesome, Bruce. I can't imagine going as far as 20kms, but the ability to do so would be ace. I guess the model would have to be up pretty high to avoid line-of-sight problems at that range, unless you are transmitting from a high hill.
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