Circular polarity is achieved by placing two yagis on the same boom, one vertically oriented and the other one horizontally oriented. Then one is fed 90 degrees out of phase with the other. In practice, either clockwise rotation or counterclockwise rotation is achieved by adding a 1/2 wavelength of feed line to one yagi while feeding the other yagi with a 1/4 wavelength of feedline.

Each antenna has a relay used to switch the addition 1/2 wavelength of feedline in or out. The relay wires for each antenna are brought into the hamshack where they lead to a switchbox. If the satellite such as AO-10 is transmitting on 145Mhz, then the 2 meter switch is flipped back & forth to determine the strongest polarity at the moment. FO-20 and FO-29 transmit on 435Mhz, so the 70 cm switch is flipped back & forth for the strongest received signal.

When transmitting in full duplex mode, you will be able to hear yourself when the satellite rises. Then flip the other polarity switch to match polarities on the uplink for strongest receive.

When your received signal strength fades, you have to guess which polarity switch to flip, if not both, but the correct guess is worth up to 3 S units!

Now, back to satellite SSTV. When receiving & transmitting SSTV, not only do you have to keep the sync pulse on 1200Hz, but you also have to keep both polarity switches in the best position. Hopefully your satellite tracking software keeps the antenna pointed in the correct direction.

Sounds complicated, and it is, but the challenge is worth it!