Fall 2005 Issue

One of the most important factors in EME communications is knowing when it is best to communicate via moonbounce. W5LUU presents a summary and table of the best and worst conditions for EME in 2006.

By Derwin King,* W5LUU
 

The earth-moon distance and the cosmic (sky) noise temperatures in the direction of the Moon are predictable cyclical variables that set basic day-to-day quality of the Earth-to-Moon path for communications at frequencies below 1.0 GHz. Best conditions occur when: (1) the Earth-Moon distance is at an absolute minimum, and (2) the Moon, as viewed from Earth, is in the coldest part of the sky. This rarely occurs. The EME signal-to-noise ratio, in dB, is usually degraded by a factor, DGRD (see below), which varies slowly with time. The 144 and 432 DGRD factors (in dB) and other pertinent EME data are tabulated in W5LUU Weekend Moondata at 0000 UT on each Sunday of the upcoming year. These are useful as a general guide to the basic EME weekend conditions. Ionospheric disturbances, local noise, polarization mismatch, and scattering properties of the Moon may make DGRD higher. The Range Factor is equal for all frequencies. Sky temperature is greater at 50 MHz than on 144 and lower on 1296 and higher than on 432.

In early 2006 the average DGRD remains high as Moon apogee occurs in the cold sky region, but by the end of the year this will reverse. In September Moon perigee occurs at a northern declination for the first time in many years. This continues for the remainder of 2006—and for the next several years. Five good weekend days occur in the first half of 2006 and eight in the second half. No weekend days are rated any better. However, these will be coming next year and for a few years thereafter. Contest dates for 2006 need to be carefully coordinated if all interest groups are to be fairly accommodated within the few feasible weekends.

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