Summer 2007 Issue

Jamesburg Earth Station EME Update

In the last issue of CQ VHF, AA6EG wrote about efforts to use the Jamesburg
dish on ham frequencies. Here is the latest on the project.

By Pat Barthelow, AA6EG

This is a spectacular “over the shoulder” nighttime view of the Moon and Venus as “seen” by the Jamesburg dish.
(Photo by Rex Allers, KK6MK)


I would really like to thank the CQ VHF magazine staff and editors for polishing and printing our Jamesburg Earth Station team’s EME story. The Jamesburg story continues. Since the article in the Spring 2007 issue of CQ VHF was wrapped, we have achieved some very successful and fun EME contest operations and experimented with some sub-optimal 144- and 440-MHz near-prime focus feeds. Our intrepid volunteer team has gained complete precision control of the dish, both in azimuth and elevation.

Within the team, our software guys—led by Kevin Hague, N5XSA, and Rex Allers, KK6MK—have refined the dish-control software, so much so that Kevin demonstrated to us how the main program keeps the very tight beam created by the 30-meter dish actually centered on the moon’s surface. Kevin created a great graphic of the moon that has a tiny dot representing the center of our beam. With the laptop joystick, Kevin steered the beam around on the moon’s surface while we listened to the return signals, and it was very cool! As expected, we could hear the return signal drop off rapidly in real time as we moved the beam off-center of the moon. This was a great reality check that told us that the beam is indeed tight and symmetrical at 1296 MHz and is correctly boresighted with the AZ/EL sensors of the VERTEX dish drive system. With this insight as to the accuracy of the program we can now lock in the beam center anywhere on the moon’s surface with ease.

We have some preliminary results from our dish metrology expert, Mike Brenner, of <>. We know from his laser measurements that the dish structure is extremely rigid, with an RMS surface change of only 10 to 14 mils between extremes of vertical angles. We hope the surface accuracy of the Italian-made Cospal panels are equally as good, but need more design dimensions of the two reflector surfaces to determine the current dish accuracy.

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