EME Schedule Planning

for Stations with Fixed Elevation Antennas

    Planning an EME schedule takes either a lot of time or a number of software tools and not quite so much time. The principle objective in planning an EME schedule is finding the best time to conduct a schedule while taking into account all of the operating constraints. Here is a list of many constraints that one will encounter in setting up EME schedules:

1. When is the moon above the horizon at both stations?

2. When is the moon in an elevation range that is useable simultaneously at both stations?

3. As a rule, tend to set up schedules at Lunar Perigee

4. What are the constraints of range in azimuth?

5. What is the range of times where EME operation is mutually allowed at both stations?

    Stations that are equipped with full AZ/EL antennas clearly have greatly reduced restrictions on access to the moon. With full AZ/EL capability, the principle constraint is finding the window of maximum opportunity with the station who has less capability.  It may seem like a daunting task to sort through all of this but let's give it a shot. 

    I have been working on schedules with a single yagi station. This station is located in grid square JO80hk, and is equipped with an 11 element yagi. As an example of setting up a schedule for an EME, let me go through the steps of finding the time for as many optimum schedules during the month of February 2003 as is possible given the hypothetical constraints of each station.

Common Moon Window

    The first step is to find the times where the moon is simultaneously in view at AA7A (in DM43ao) and the station in JO80hk. To calculate the times that the moon is above the horizon, I use Nova for Windows, from Northern Lights Software. This software has a utility to calculate the common window times for satellites and for celestial objects. Entering the location of AA7A and a station in JO80 into the setup screen, the program creates a list of times where there is a common visual moon at both locations. For the month of February 2003, here is a table containing the results of the program:

Table 1 - Calculated times for common view of the moon for AA7A and a station in JO80

    This table has a few interesting results that are worth mentioning. There are two gaps in the chart where there are days when it appears that there is no common moon. Note that there is no listing for 15 February. This is slightly confusing for people who keep track of time using the sun. The sun rises every day but there are some days when the moon does not have a moonrise. The moon actually rises about an hour before the start of 15 February (using GMT) and the next moonrise is 2 minutes after the start of 16 February. So, when looking at moonrise lists, keep in mind that the moonrise times can precess across a day. The second gap is across the days of 25 through 27 February. In that interval of time, the moon is in its most southern declination and the moon sets in JO80 before it rises at AA7A for those three days. Obviously, those days are instantly ruled out as days for setting up a schedule.

    If both AA7A and the station in JO80 had antenna systems that permitted tracking the moon at all Azimuth and Elevation angles, then we would be about done with the analysis. However, neither station is so equipped and we need to look at some more information.

Elevation Pattern Analysis

    If you have scanned other sections of this project page, you will note that the current 6 meter EME antenna at AA7A has a fixed Elevation angle of approximately 26 degrees. A view of the predicted antenna gain as a function of elevation angle is shown in the figure below.

Figure 1 - Calculated elevation plot of AA7A 6m EME antenna

    This plot suggests that the antenna at AA7A has its best gain between the elevation angles of 5 and 33 degrees. Other analysis suggests that the gain in the lower lobe (around 9 degrees elevation) is reduced due to sagging of the rope yagi and finite ground conductivity of the soil in Arizona. For optimized scheduling, I have been using only the range of elevation from 18 to 33 degrees. What this suggests is that of the common lunar window times shown in Table 1, above, the available schedule times are restricted to those where the moon is in the elevation range of 18 and 33 degrees at AA7A's QTH. If the DX station had full AZ/EL antenna capability, once again we would be done with the analysis. However, at this time, that is not the case and we move on.

    For this example, we are assuming that the DX station uses a very large six meter yagi. This yagi is assumed to have 11 elements on a 17.7 meter (58 foot) boom. In free space, this antenna has a peak gain on bore site of around 18 dbi. When this antenna is mounted over conductive soil, the antenna pattern will be affected in two ways: 1) it will pick up "ground gain" which is the term for gain in excess of the gain of the antenna in free space derived from reflections from the ground and 2) it will exhibit lobes in its vertical pattern above the main lobe. In general, as a hoizontally-polarized antenna is mounted higher over conductive soil, the number of vertical lobes increases and the gain in the first lobe above the main lobe decreases. The predicted elevation pattern of this antenna is shown in the figure below.

Figure 2 - Calculated elevation plot of DX station's 6m antenna

    Notice that the gain of this antenna at an elevation angle of 6 degrees is a whopping 20.66 dbi. This is an impressive amount of gain, but it is only available when the moon is in the elevation range of 2 to 10 degrees, roughly. The first vertical lobe of his antenna is also quite useful for EME work, as well. The gain of the first lobe at an elevation angle of 16 degrees exceeds the gain of AA7A's antenna in its main lobe by almost 2 db. So, in planning the time period in which the moon is available JO80, the moon is "in  view" of his antenna when the elevation angle is between 2 and 19 degrees. Going back to work on Nova for Windows, I entered the minimum and maximum elevation angles at AA7A (18 and 33 degrees) and in JO80 (2 and 18 degrees), I get the information provided in the table below.

Table 2 - Predicted times when moon is in common view of AA7A and DX station's antenna pattern

    Once again, there is a lot of information in this Table 2 that has a bearing on selecting an optimized scheduling time. First of all, note that there are only 7 days where there is any time when the moon is in view of both antennas. This is substantially less than the range suggested in Table 1.And, on only 5 of those 7 days is there a time duration of more than just a few minutes. 

Perigee Scheduling

    The moon is in a slightly elliptical orbit around the earth. Table 2 shows the values of distance (in km) to the moon. Over the period of a month, the path loss due to changes in the moon's distance from the earth varies about 3 db. In general, it is advisable to run schedules during the period of time closest to Perigee. In Table 2, February 19 is only 3 1/2 days after Perigee (relatively close). So, February 19 and 20 would be good days to use that would have the least amount of path loss. While February 4 thru 6 have good visual window times, these days are near Apogee and will be less than optimum due to the additional losses due to lunar distance.

Azimuth Range Limits

     For some (such as AA7A), antennas do not swing in full azimuth. Expeditions using temporary antennas may only be able to set up to run in specific directions. Keep these in mind when setting up schedules. Expeditions will start using JT44 on EME and it is wise to keep sharp on how to take into account antenna aiming limitations

Operating Time Limitations

    There are also time limitations in setting up schedules. Since EME uses high power, some operators are constrained to operate in quiet times after TV sets and other appliances are usually off. And, some of us still need to work to support our hobby and setting up schedules during working hours can may not always be permitted. 

Summary

    After taking all of this into account, do not be surprised that the schedule times to some stations are minutes a month. It is hard to set up generalizations about scheduling. Let me try a few:

• There is no common lunar window with stations at your antipode

• Stations that are closer to you (less than 4,000 km) may be harder to find common lunar windows than stations that are far (more than 4,000 km)

• Close stations that are north or south of you are easier to find schedule windows than those who are east or west of you (unless someone can elevate their antenna)

• Every day at moonrise, the moon is in the process of setting somewhere...hopefully where there is an available station.

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