[amsat-bb] CP vs. LP and all that implies

Bill Attwood whattwood at gmail.com
Thu Jan 22 16:40:23 UTC 2015


Wow, great post Daniel!  That answers a bunch of questions I had myself 
- I was thinking RHCP would receive better than a H/V combination but it 
looks like that is not the case.

73,
Bill VE6WK


On 1/22/2015 3:29 AM, Daniel Cussen wrote:
> Best info on-line I found here:
>
> http://sv1bsx.50webs.com/antenna-pol/polarization.html
>
> Note the losses of having the wrong circular polarisation from a
> polarised source are very high. In the real world the antenna may not
> be perfectly polarised on one end, so difference may not be as great.
>
> One very useful/recommended setup for circular is school contacts on 2
> metres with the space station. It is recommended to be able to switch
> polarisation in the middle of a school contact as sometimes the signal
> is not direct but reflected off a solar panel. In this case you may
> need to suddenly switch polarisation.
>
> I have a wimo 2m 6 element X circular antenna with the switching kit.
> The antenna is extremely light and designed to be mounted at the very
> rear, to prevent the boom interfering in the signal. I was not that
> impressed by the elements strength, guessing a bird might be able to
> bend them by landing on them. The driven element is made from a few
> parts screwed together. I worry corrosion would quickly make it
> unreliable. Being limited to 6 elements and quite short a longer
> linear model may work nearly as good.
>
> http://www.wimo.de/xquad-antennas_e.html
>
> also:
>
> http://www.wimo.de/power-splitter-combiner_e.html#18038
>
> The 70cm model I have heard is much better in that the driven element
> is stamped rather than assembled so less joins to corrode. Also being
> smaller the elements are stronger.
>
> The switch box is designed to be mounted on the mast near the antenna
> meaning only one coax cable per band needs to be ran out, but then you
> need DC multicore to switch polarisations. You can select V, H, LHCP,
> RHCP. One downside is that they do not give the option of a control
> box, so you need to build one by hand. You need to ensure you do not
> transmit while switching.
>
> All in all it is quite expensive, complicated and messy. Unless you
> had an inferior setup, and found it lacking I probably would not
> bother. You only lose 3dB using linear when the source is true
> circular, so probably not really worth it unless you have maxed out on
> antenna gain/ receive pre-amps. There are additional losses with
> switches connectors etc.
>
> I have never seen/used the M2 setup so I cannot comment on this. They
> definitely seem to have more elements as a possibility.
>
> At least with the switching option you can compare the signal on
> different polarisations to see if it does help in the real world. You
> could always try it on one band, then apply it to both bands if you
> get a big difference.
>
> What do others think?
>
> Dan EI9FHB
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