Winter 2003 Issue

Photo B. The EME array at K6PF consists
of four x-pol Yagis with a mast-mounted
preamp and relays and TV camera.

Through recent developments in technology, contacts using the Moon as an RF reflector are possible even with a modestly equipped station. K6PF describes some of the associated innovations and challenges.

By Bob Kocisko,* K6PF

Living here in southern California on the west coast of the United States presents some geographical challenges for working DX on 2 meters. Of course, this applies to living anywhere when operating 2 meters DX. Propagation via the direct path, tropospheric and meteor scatter, along with sporadic-E have distance limitations. Achieving WAS (Worked All States), WAC (Worked All Continents), and DXCC awards is impossible when these are the only propagation modes being utilized on this popular VHF band.

With a half-million-mile round-trip path, EME (Earth-Moon-Earth) or moonbounce is the ultimate DX. Many weak-signal (CW and SSB) operators already have a station capable of limited 2-meter EME operation. The objective of this article is to inspire and motivate many hams who are already working, or wish to start working, weak signals on 2 meters to try EME in order to work a lot more DX, including many more grids, states, and countries. In addition, the tools needed to be successful with 2-meter EME will be presented. Let’s get started!

The Nature of EME Basic Technical Aspects

If two stations have adequate equipment and both can see the Moon at the same time, they should be able to make contact via EME. However, several attempts may be required to achieve success. Signals are very weak echoes reflected from the Moon’s surface. Typically, they are at the noise level, or even beneath the noise, occasionally rising from the noise for brief periods. Let’s look at some of the technical factors that affect EME communications, particularly as they relate to 2 meters.

Polarization. The polarization of EME signals is changing constantly, which can result in no signal being heard or very deep QSB. There are two basic types of polarization:
Spatial Polarization—Spatial polarization is a function of geometry. The wavefront of an EME signal between two stations can be rotated in polarity. The amount of rotation depends upon the relative longitudes of the two stations and the position of the Moon in the sky. Most computer Moon tracking programs calculate the amount of spatial polarization and can show the optimal times to arrange skeds (schedules).

Faraday Rotation—The Earth’s magnetic field causes the wavefront from the radio signal to rotate in polarization several times as it passes through the ionosphere on the way to the Moon and back, causing a cyclic fading in the received signal. At 2 meters the fade period between signal peaks (i.e., the time to rotate through 90 degrees) is about 30 minutes. At this time Faraday rotation cannot be predicted by computer software.

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