Ask Dr. SETI ®
This weekend I installed my new 8 foot antenna in my terrace. For now, I have set the antenna over a concrete base with an equatorial mount. I may have the oportunity of motorize the mount, with one actuator in equatorial mode, and in the future with two actuators will have az and el with a bit of modification of the mount.
For the moment I have a helix feed and I listen without problems to GPS, INMARSAT and WEFAX signals.
Now I'm a bit confused about the orientation of the antenna. For the moment I will try to put it in bird-bath mode, because is the more cheap and easy.
I don't know if I can put the dish in bird-bath, because the mount only permits up to 70º of elevation. I can try to modify the mount to get to 90º. In the future, I would like to mototize the mount, but I don't know if this is a good idea, or if the effort and the investment justify the results.
The Doctor Responds:
So, here's how I modified the arrangement for meridian-transit radio astronomy: I simply rotated the dish and mount 90 degrees on their pipe. This turned the declination turnbuckle into an azimuth (RA) adjustment, and the RA rotor into an elevation rotor. I set the turnbuckle for 0 degrees offset from meridian transit (that is, so the dish runs along a true North-South line), and I use the former RA rotor to move the elevation from the Southern horizon to the North polar star (about a 135 degree range at my latitude). Now, using the chain drive to set declination, and the Earth's rotation to set RA, I can scan just about anywhere in the Northern sky, as long as I don't mind waiting 24 hours (acutally, 23 hours 56 minutes; one sidereal day) for the object of interest to rotate into view.
I did find with this arrangement that the dish was quite front-heavy at low elevation angles, and put quite a strain on the elevation (formerly RA) rotor. I ultimately had to mount a counterweight on an arm extending back from the rear of the dish, to provide better balance.
I hope you find this description useful. Good luck with your system, and congratulations on your progress to date.
entire website copyright © The SETI League, Inc.; Maintained by Microcomm
this page last updated 12 November 2005
Top of Page