circular polarized antenna hype

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circular polarized antenna hype

Tilman Baumann-3
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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Re: circular polarized antenna hype

Aka-7
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 <[hidden email]>
> An: [hidden email]
> 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
>
> _______________________________________________
> Paparazzi-devel mailing list
> [hidden email]
> https://lists.nongnu.org/mailman/listinfo/paparazzi-devel

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Re: circular polarized antenna hype

Tilman Baumann-3
On 23/07/12 14:47, Marc Schwarzbach 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 :-)

True. Eventually I would like to invest in a antenna tracker at the
ground station.
>
> I have no problems with 2.4GHz Xbees with standard wire antennas up to 1km.
>
> Do you have problems with your connection?

Not really. But since I fly 2.4Ghz the range is not terribly long and I
wonder if I might get better reception at the fringes of the range.

Anyway. I just wonder if the wondrous advantages the FPV guys keep
harping around would apply to us. :)

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Re: circular polarized antenna hype

Reto Büttner
Hi Tilman

I get over 15km perfect reception using 2.4 GHz XBee and a 14 dBi
linear polarized patch antenna on the ground station and a standard
whip antenna on the aircraft. Do you need any more?

At long range flight the antennas are parallel (in phase), as the
aircraft will be flying horizontally. You most probably will not be
performing aerobatics at long range. At short range, where you might
want to try some tighter turns, reception is no problem anyway.

Antenna tracking was no issue for me so far. At long range it is no
problem to manually track the antenna as things go very slowly. At
short range you don't need antenna tracking.

Happy landings,
Reto

2012/7/23 Tilman Baumann <[hidden email]>:

> On 23/07/12 14:47, Marc Schwarzbach 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 :-)
>
>
> True. Eventually I would like to invest in a antenna tracker at the ground
> station.
>
>>
>> I have no problems with 2.4GHz Xbees with standard wire antennas up to
>> 1km.
>>
>> Do you have problems with your connection?
>
>
> Not really. But since I fly 2.4Ghz the range is not terribly long and I
> wonder if I might get better reception at the fringes of the range.
>
> Anyway. I just wonder if the wondrous advantages the FPV guys keep harping
> around would apply to us. :)
>
>
> _______________________________________________
> Paparazzi-devel mailing list
> [hidden email]
> https://lists.nongnu.org/mailman/listinfo/paparazzi-devel

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Re: circular polarized antenna hype

Chris Gough-2
In reply to this post by Aka-7
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" <[hidden email]> 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 <[hidden email]>
>> An: [hidden email]
>> 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
>>
>> _______________________________________________
>> Paparazzi-devel mailing list
>> [hidden email]
>> https://lists.nongnu.org/mailman/listinfo/paparazzi-devel
>
> _______________________________________________
> Paparazzi-devel mailing list
> [hidden email]
> https://lists.nongnu.org/mailman/listinfo/paparazzi-devel

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Re: circular polarized antenna hype

Tilman Baumann-3
In reply to this post by Reto Büttner
On 23/07/12 15:07, Reto Büttner wrote:

> Hi Tilman
>
> I get over 15km perfect reception using 2.4 GHz XBee and a 14 dBi
> linear polarized patch antenna on the ground station and a standard
> whip antenna on the aircraft. Do you need any more?
>
> [...]
> Antenna tracking was no issue for me so far. At long range it is no
> problem to manually track the antenna as things go very slowly. At
> short range you don't need antenna tracking.
>
>
That sounds good enough indeed.

Maintaining line of sight can be tricky of course. But that is a 2.4Ghz
problem, no matter what antenna.
Where I'm currently flying I can easily get behind dense tree lines and
a small hill. :-/

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Re: circular polarized antenna hype

Chris Wozny-3
In reply to this post by Tilman Baumann-3
Tilman,

After looking at David Windestål's guide on the Skew-Planar wheel and
Cloverleaf antenna, he recommends using the SPW for the receiver and
the Cloverleaf as the antenna. The reason for this being that "the
reverse polarization rejection pattern is very erratic [for the
Cloverleaf antenna] and varies between -8 and 19dBi. Therefore there
are better antennas to choose for the receiver [such as the
Skew-Planar Wheel]. This doesn’t matter for transmitting signals
though, only for receiving them." Also, he encourages the use of
circularly polarized antennas for Tx and Rx which answers your other
question.

I'm very curious about the probability of two circularly polarized
being out of phase, my initial guess would be that the chance of this
incident is very small (if possible at all.) That's just a guess
though so I'll leave the actual technical answer for one of the RF
gurus.

Also, here's a pretty awesome video about antenna polarization if
anyone wants to know more about it: http://vimeo.com/8826952

Cheers,
Chris

On Mon, Jul 23, 2012 at 9:30 AM, Tilman Baumann <[hidden email]> wrote:

>
> 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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Re: circular polarized antenna hype

Chris Efstathiou
In reply to this post by Tilman Baumann-3
Anyway i have done some tests with a home made yagi about 13cm long with
2mm elements
(9dbd) and an airborne antenna tracker using a servocity spt50 pan unit
(very small and light) under the fuselage.
Yagi calculator here:
http://www.k7mem.com/Electronic_Notebook/antennas/yagi_vhf.html
Horizontal polarization also helps as most of the man made noise is
vertically polarized.
It is the best solution for video as telemetry was never a problem for
me at least.
The next best solution is to use the 1.2 ghz band
Chris



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Re: circular polarized antenna hype

Reto Büttner
In reply to this post by Tilman Baumann-3
Hi Tilman

This weekend I sucessfully tested my setup over 25 km (10 km more than
last time):

- 2.4 GHz XBee Pro
- 14 dBi linear polarized patch antenna on the ground station
- Standard whip antenna (just the 1 inch wire) on the aircraft. The
antenna vertical, perpendicular to the ground plane and in free air
(not in the fuselage nor near to any other disturbing objects).
- 9600 baud
- Default telemetry

If you want to be able to loose line-of-sight to the groundstation
consider DroneCell:
http://store.diydrones.com/DroneCell_p/br-dronecell-01.htm
Be aware of legal restrictions concerning flying out of sight.

Cheers, Reto

2012/7/23 Tilman Baumann <[hidden email]>:

> On 23/07/12 15:07, Reto Büttner wrote:
>>
>> Hi Tilman
>>
>> I get over 15km perfect reception using 2.4 GHz XBee and a 14 dBi
>> linear polarized patch antenna on the ground station and a standard
>> whip antenna on the aircraft. Do you need any more?
>>
>> [...]
>>
>> Antenna tracking was no issue for me so far. At long range it is no
>> problem to manually track the antenna as things go very slowly. At
>> short range you don't need antenna tracking.
>>
>>
> That sounds good enough indeed.
>
> Maintaining line of sight can be tricky of course. But that is a 2.4Ghz
> problem, no matter what antenna.
> Where I'm currently flying I can easily get behind dense tree lines and a
> small hill. :-/
>
>
> _______________________________________________
> Paparazzi-devel mailing list
> [hidden email]
> https://lists.nongnu.org/mailman/listinfo/paparazzi-devel

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