Dave G0CBK gave us a very insightful talk on Thursday 9th July on the topic of Earth-Moon-Earth contacts.
We heard how Dave built up his station, starting out with a pair of Yagi antennae, and making his first contact with a station that had a very large dish. Eventually Dave upgraded his station so that he became able to make contacts with stations of a similar size to his own. Part of the problem is the large path loss with this propagation mode, which results in small stations being unable to hear each other.
Stations that use Yagis suffer from changes in signal polarity caused by the radio waves being reflected from an uneven and moving surface. The use of circular polarisation and dish antennae helps to overcome this problem. Despite this, the receivable signal is still very small, and often “in the noise”.
Dave described how he constructed his current dish antenna, the mechanism used to move the dish to track the moon, and how the doppler shift caused by the motion of the moon can be accounted for.