Satellite Antenna

The project would be incomplete without a brief description of Amateur antennas for satellite work. Amateurs have used several types of antennas for working with satellites, from a short whips to large dishes. However a common type of antenna to obtain the requisite gain and directivity is an Yagi array.

A typical Yagi array consists of a Driven element, a Reflector and one or more Directors. The number of directors can be increased to achieve a narrower beam and higher relative gain.

The driven element is a half wave dipole, and so its length is easiest to handle at very high frequencies (VHF), 100 MHz and higher. At 150 MHz, the driven element is about 38 inches long.

Amateur satellites are about as big as a 2 foot cube if not smaller, they are not the complex ones shown in Sci-Fi or bond movies. Satellite makers realize this and most of them have set their radio frequencies in the VHF and UHF range. A quick visit to amsat.org will show a list of satellites and their operating frequencies. They have also separated the uplink frequencies and downlink frequencies and assigned one to the VHF band and the other to the UHF band, assuming of course you know what is VHF and UHF bands, if not just do a web search for amateur bands.

So it seems we will need two of the Yagi array antennas one for the uplink and another for the downlink, typically one in the VHF band and the other in the UHF band. The picture below shows these two antennas mounted on either side of the supporting boom.

Click picture for bigger image

I found the Tape Measure beam was the easiest to build and best option for VHF band. A 3-element beam provided enough gain and beam width for the VHF band. The driven element used a hairpin match and attached directly to the coax cable. This made it very easy to build the cross beam required for working satellites.

The Easy Yagi was a great design for the UHF band. It used short pieces of 1/8 inch copper tubing and soldered directly on to the coax cable as well. At UHF frequencies a 3-element was ery short so I elected to go for a 6-element beam instead. I figured, the additional gain would compensate for higher coax losses at these frequencies. With this arrangement, it was easy to construct a light weight 6-element cross beam.

I owe the following articles for almost everything I learned about these wonderful designs.

Easy Yagi

http://www.fredspinner.com/W0FMS/CheapYagi/vjbcy.html

Cheap & Easy Yagi Antennas

http://www.amsat.org/amsat-new/information/faqs/crow/

Tape Measure Beam

http://theleggios.net/wb2hol/projects/rdf/tape_bm.htm

Antenna Polarisation with Cross Beams

http://sv1bsx.50webs.com/antenna-pol/polarization.html

PS: In this project, the Tape Measure Beam worked out to be a great choice for the 2 meter beams, while the Easy Yagi worked best for 70 centimeter beams. The article on cross beams was the easiest to understand and finally build some good cross beams.

You will find the Yagi CAD mentioned in the Tape Measure Beam article an EXCELLENT beginner's tool for adjusting the beam antenna lengths.

I'm not sure if I will be able to answer any questions about the articles themselves, however I can try to answer any questions regarding my experiences in building these. I can be reached by email at k6vug@sbcglobal.net