Tuesday, July 6, 2010

Microwave and EME

The microwave range has, for many years , been synonymously related to amateur moonbounce activities . Centering on the 70-cm, 23-cm and 13-cm bands, amateurs have often successfully communicated over this Earth-Moon-Earth path. The parameters associated with moonbounce are many: they include considerations of atmospheric losses, faraday rotation, moon-encountered losses, galactic noise interference, etc. A general outline of these parameters is illustrated in Fig. 1-6.

The Earth-Moon-Earth distance varies between 225,000 miles (perigee) and 250,000 miles (apogee), producing fluctuations of up to 2 dB of reflected signals-a difference between communicating and not communicating via this difficult path. The EME signal is also masked by a variety of noises and requires top-notch earthstation setups plus high-gain antennas and high transmitted power levels for ensured success. The minimal acceptable rf-output power is 400 watts, and the minimal antenna-gain figure is 20 dB. These parameters do not allow any leeway for additional signal fades or noise, thus one can logically surmise that EME communications reflect extreme challenges for only the stout hearted!

Fig. 1-6. Some of the many parameters affecting uhf and microwave EME signals.

The full aspects of EME communications are beyond the scope of this book, thus the reader is referred to more specialized works in this particular area. Rest assured that additional information and equipment for EME operations will be a natural part of tomorrow 's innovations.