Fall 2003 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 2004.

By Derwin King,* W5LUU

While a number of factors affect EME communications, the distance from the Earth to the Moon and the cosmic noise temperature in the direction of the Moon are predictable, cyclical variables that set the basic day-to-day quality of the Earth-Moon path. Other things being equal, best EME conditions occur when the Moon is: (1) at the best possible perigee and (2) near the RA and DEC (see definitions below) of the coldest sky along its path. Signal-to-noise degradation (DGRD) from these two variables, in dB referenced to the best possible conditions, are tabulated in the accompanying table, along with other pertinent data. These are for each Sunday at 0000 UTC to provide a guide to the 144-MHz and 432-MHz weekend conditions in 2004.

In 2004 the average DGRD continues to increase as Moon perigee occurs at increasing RA and at southern declinations where the sky noise (temperature) is generally higher. Moon apogee occurs at northern declinations. This trend will continue for the next two to three years as the average position of perigee moves ~2.7 hours RA per year along its nine-year cycle. DGRD will again be very low for several days each month in 2007– 2010 as perigee occurs within a few hours RA of cold sky.

Meanwhile, don’t give up. While there are no Excellent or Very Good days in 2004, many days are rated Good with DGRD of 1.8 to 2.5 dB. Early in the year the Good days occur at moderate, north declinations, but in the last few months several are at southern declinations with RA of 21–24 hours. Two or three weekends with north declinations are potentially usable for the ARRL contest, but for all, EME will be mostly a daylight operation. These dates are: September 11–12, October 9–10, and November 6–7. Also, September 25–26, October 23–24, and November 20–21 have Good conditions and the Moon at night. September 25–26 allows EME from most of Europe to VK and ZL (for a short period), but not for as many hours as for any of the three north declination dates. Good luck and enjoy!

The following are definitions of terms used in the accompanying table:

DEC (deg): This is the Moon declination in degrees north and south (–) of the equator. This is cyclical with an average period of 27.212221 days. The maximum declination during a monthly cycle is also cyclic, with a range of 18.15 to 28.72 degrees and a period of about 19 years. The next maximum is in September 2006.

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