Friday, April 14, 2017

Pointing my EME Antennas at the Moon

EA4TX ARS-USB Rotor Controller
Once you have the 2-M antennas in the air, you need to figure out how to rotate them to track the moon.  Back in the early 1980's when I was first on 2-M EME, it was a major thing to know where the moon was at any particular point in time.  Remember, there were NO Smartphones and NO Internet at that time - yep, it was the "Dark Ages." 

At first, I had to use the Nautical Almanac to find the Greenwich Hour Angle (GHA) and use that to calculate BY HAND the moon's position.  After a short time I acquired a printed copy of a BASIC computer program from Lance, WA1JXN/7, (now W7GJ), which was written for his Apple II home computer.  I converted that to Commodore BASIC and typed it into my Commodore Pet 2001 home computer.  I could now print out the Azimuth and Elevation headings for the moon.  This was done in increments of 10 minutes.  Then, to track the moon I had to manually turn the two rotors to the headings shown on the printout and then remember to keep incrementing the rotors as the moon moved.  I also needed to watch the clock and manually switch from receive to transmit at the end of each period.  Often I was not sure the antennas were on the moon so I ran out in the yard and eyeballed it.  It was a lot of work!

MoonSked Sked Maker Window
Boy, have things changed now!!  The home computer now will calculate the position of the moon every SECOND.  It will send that information over USB to the EA4TX ARS-USB Rotor Controller (shown at the upper right.  Click on any photo to see it larger.)  That device is connected to the Azimuth Rotor Control Box and the Elevation Rotor Control Box.  As the moon moves, the ARS-USB will turn the rotors automatically.

EA4TX Graphical Interface
The program that I use to track the moon is MoonSked by GM4JJJ. Not only will it track the moon in realtime but it will calculate a suitable date/time for setting schedules with other stations (the Sked Maker window is shown at the left), it will create a sky map showing the moon's location (to help determine when the moon is in a favorable location), it will search a database of EME stations for a partial call, and it will display a World Map with the moon's ground-track shown.  But, one of the coolest things (in my opinion) is that it will ONLY send the tracking information during transmit (TX) periods!  That way any potential noise being generated by the rotors will not affect the receiver.
Remote Ant. Control
The EA4TX Rotor Controller has a small graphical interface for displaying the antenna positions (shown at the right.)  And, with this interface you can control the rotors by using the mouse or by pressing the buttons on the front panel.

All the above will automate the pointing of the antennas and let me concentrate on the actual operation of the MAP65 software to make the EME QSO's.  When you think about operating moon-bounce for hours at a time, the ability to have the antennas continuously track the moon is huge!  Sometimes I think back to the days when I had to actually calculate the moon's position by hand and later from a printout made by my home computer, and compared to that, this is heaven!

One final thing I wanted to have was someway to control the pointing of the antennas from outside the house.  The antennas are mounted on a Hazer tram system and the tower is right next to the house.  When raising and lowering the Hazer, someone needs to manually rotate the antennas (especially the Elevation rotor) to make sure the antennas do not hit the house or the ground as the Hazer is raised or lowered.  I was planning on building a box to mount at the base of the tower with four switches (UP, DOWN, LEFT, and RIGHT) and wire them to the EA4TX Rotor Controller.  While looking on eBay for some suitable small switches, I found the Rain Proof Hoist Crane Pendant shown at the left.  WOW!  Was this exactly what I needed or what?  This item was New and would be shipped to me from Hong Kong.  The price?  Trust me - you will NOT believe it!  Including shipping I paid a whopping $8.15 for this!  WOWZER!

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