SM 5 BSZ - Electronic Polarisation Control
(April 25 1997)

#### Theory for use of polarisation control

Electromagnetic radiation is polarised. - Or is it not ? This issue is far more complicated than one might think at a first glance. When we receive "unpolarised" galactic noise, our antennas create polarisation because we use linear receivers, and they have full sensitivity for a wave with one particular polarisation - and zero sensitivity for a wave with the orthogonal polarisation. If you are interested in polarisation, and how it relates to detection of weak signals in noise, look here What is Polarisation ? Signals vs Noise For a rather long, but fairly non- mathematical discussion.

It is not very complicated to use polarisation control look here for an explanation how it works How to Select Polarisation for EME for aurora and sporadic E it is much easier Polarisation Control for Aurora gives some background, and my experiences so far.

Cross yagis are often used for circular polarisation only. This is nearly always a bad idea, look here why: Circular vs linear polarisation.

#### Simple Practical Polarisation Control

The obvious and most simple solution to polarisation control is to use two antennas of orthogonal polarisation and switch between them by use of a relay. This is probably a perfect solution on 1296MHz for EME, where circular polarisation is used. On lower bands linear polarisation is used by most stations, and then switching between a pair of orthogonal, linearly polarised antennas will cause a 3dB loss now and then. Still simple switching systems are very useful. As compared to a single polarisation, they literally open a new dimension to the EME'er. There are different solutions, look here for details: Simple Polarisation Switching By the addition of a second pre amplifier and a second transmit receive relay, a lot more flexibility is possible. The transmit options are still limited, but new possibilities arise on the receive side just by adding simple, low level components. Separate Polarisation Switching for Tx and Rx