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Re: [Paparazzi-devel] circular polarized antenna hype


From: Chris Gough
Subject: Re: [Paparazzi-devel] circular polarized antenna hype
Date: Tue, 24 Jul 2012 00:13:08 +1000

We tested them in our OBC rig (8+km requirement) and ended up not going with 
them on any link because we could get sufficient range with dipoles and 
amplifiers wound up to legal EIRP limits, and that seemed simpler and more 
robust.

The 900 MHz cloverleaves are big and cumbersome, easily detuned, not very 
practical.

Didn't try 2.4ghz ones, only using that for RC in visual range. Those little 
circular polarized patched are cheap and might be worth a try on the ground, 
with the usual rubber duck dipole or monopole in the air (e.g. <$20 from 
flytron).

5.8 Ghz cloverleaves are compact and potentially interesting, we almost went 
with that on our high bandwidth link (Ubiquity Bullets) and still might resort 
to using them at both ends of that link if we are getting issues with 
congestion.

Chris Gough

On 23/07/2012, at 11:47 PM, "Marc Schwarzbach" <address@hidden> wrote:

> Hi Tilman,
> 
> the basic principle of loss of signal strength when two linear antennas are 
> out of phase applys to XBee, too, of course. So you could avoid that by 
> spending a constant loss of 3dB when using a circular polarized antenna on 
> one side.
> 
> In my oppinion it makes sense when using a higher gain circular on the ground 
> (patch or helix) and a standard omni on the plane.
> I´m a little sceptical with all the hype around cloverleaves and so on... 
> Also look fragile when used on the plane :-)
> 
> I have no problems with 2.4GHz Xbees with standard wire antennas up to 1km.
> 
> Do you have problems with your connection?
> 
> Cheers
> 
> Marc
> 
> 
> 
> 
> 
> -------- Original-Nachricht --------
>> Datum: Mon, 23 Jul 2012 14:30:56 +0100
>> Von: Tilman Baumann <address@hidden>
>> An: address@hidden
>> Betreff: [Paparazzi-devel] circular polarized antenna hype
> 
>> What is up with those circular polarized antennas that are all the rage 
>> in the FPW world right now?
>> http://www.fpvuk.org/equipment/circular-polarized-antennas/
>> 
>> The problems they are trying to avoid should be present in telemetry as 
>> well. Which is loss of signal when antennas are out of phase. (Vertical 
>> vs. Horizontal)
>> 
>> I wonder, would it make sense to hook one of those cloverleaves to a 
>> XBee? How does the fact that we use bidirectional signals the efficiency 
>> of those?
>> Has anyone tried? Should trials be made?
>> Do I understand correctly that only one side should be circular 
>> polarized? Or should have receiver and transmitter the same antenna?
>> 
>> I thought I bring that up since it has not been discussed here as far as 
>> I know. I'm curious in your opinions.
>> 
>>  Tilman
>> 
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> 
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