This is a version of my article in DUBUS 3/1996.
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How to Use Polarization Rotation
It is only in the past 10-15 years that we have learned how to use polarization rotation effectively. KL7WE explained exactly how to do this [5, 6].
It's a simple three-step process:
You never need to rotate more than 90°. If the rotation is more than 90°, it is quicker to rotate (180 - x)° in the opposite direction.
If you don't have a sked, how do you do Step 1? How do you know the geometrical polarization rotation for the next station you are going to work?
This is very easy, because you don't need to know exactly where the other station is. For every 30 minutes during the moon window, my moon tracking software  prints out the geometrical rotations for some locations that are known to be active - or countries that I badly need! Moving from east to west, my current list is:
VK, JA, 9M2, 4X, A22, ZS6, PY, W1, HP, W4, W5, W0, W7, W6, KH6.
It's easy to add other countries as required. The software prints out the geometrical rotations for these countries, whenever we can both see the moon.
From my QTH, anywhere in Europe has a geometrical polarization rotation close to 0°. VK and ZL are always close to 180°, which of course is the same as 0°. JA is usually close to 90° (but take care - some JA stations are vertically polarized!).
VK3UM's EME software now has a real-time display of geometrical rotations between your QTH and almost every DXCC country.
How to call a station
Simply follow these instructions:
How to call CQ
You want your signals to arrive in the DX location with horizontal polarization.
Although most stations can not rotate polarization quickly enough to optimize their own echoes (only 2.5 seconds available), you can tell the direction of rotation by rolling the array as you transmit and listen for your echoes. Unless Faraday rotation happens to be zero, one direction of rotation will give distinctly stronger echoes. You can also estimate the amount of polarization rotation from the strength of your own echoes. If echoes are good, the rotation is probably less than 45°. If echoes are poor or absent, the polarization rotation is probably close to 90°, so your best strategy for working horizontal yagi stations in your own continent is to rotate the array to vertical; this will be the optimum polarization for both RX and TX.
Because the polarization can always be accurately optimized, my small antenna with 12 short yagis will often perform as well as a much larger fixed horizontal array. With only 700W, I have worked many new stations that would have been impossible without polarization rotation. In contests, this array gets to places that fixed polarization cannot reach!
I have always kept records of the TX and RX polarization. Many of the extra QSOs would have been possible with switchable horizontal/ vertical polarization, so this is a good compromise. But some of the most important QSOs - with small stations in new US states and countries - have required the full rotation capability.
Being able to rotate the polarization to any angle also gives you a much more accurate understanding of propagation conditions and band activity. Most important of all, you are never trapped by unfavourable Faraday rotation.
Polarization rotation has literally added another dimension to the pleasure of EME operating!
Updated 18 April 2010
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