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Ask Dr. SETI ®

Chapter 6: Technology

Where Should I Point My Dish?

Dear Dr. SETI:
I am setting up my Project Argus station. I have some problems, because my backyard is a bit small, and I will have trouble rotating my 2.45 meter dish in some directions. Which is better, to have a smaller dish that I can move to track celestial objects, or a larger one, fixed in position? Also, if I put the larger antenna in a fixed position, what is the best azimuth and elevation position for drift-scan mode?

Iban (Spain)

The Doctor Responds:
Almost all of our members opt for a larger dish, Iban, and generally operate successfully in meridian transit (drift-scan) mode. Many simply point the dish straight up ("bird bath" mode). As long as there are stars in the general direction of "up", then this is as reasonable a strategy for all-sky surveys as any other.

For any fixed antenna, I believe the best azimuth to use is 0 or 180 degrees true, because this will give you meridian scan. That is, your Local Mean Sidereal Time will be equal to Right Ascension, which simplifies all astronomical calculations.

As for elevation, most of our members just point straight up, 90 degrees from the horizon, which sets their declination equal to their latitude. In addition to simplifying the mathematics, this has the added advantage of minimizing wind loading on the antenna. But you can really use whatever elevation is convenient, that will keep your antenna clear of obstructions.

Remember, there are no wrong directions for SETI, except "down", which might be your choice for SSTI (Search for Sub-Terranean Intelligence)!

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