The following article was originally presented at a Project OSCAR seminar on September 30th, 1990. AMSAT-UK printed an abridged version of this presentation in their OSCAR News, Number 88, April 1991. The original presentation has been reedited and updated for AMSAT's Web page.
Years of home brewing has taught me how to do and not to do a lot of things properly. This experience, along with reading AMSAT- NA, AMSAT-UK and ARRL publications (Note 1) has taught me how to build my projects better. Here are some tips I learned that may be of help with the most important part of an amateur radio satellite station, the antenna systems.
Low Cost Satellite Antennas
Materials to build satellite antennas can sometimes be found among junk most people would throw away. An old broken-off car radio antenna I found lying in the street became the vertical element of a two meter 5/8 wave groundplane for mode A and T. Four wire clothes hangers became the radials. Likewise all the remaining components were "salvaged" from other junk I had collected here and there. I used this simple matching network:
All you need to build a simple VHF or UHF 1/4 wave groundplane antenna is a coax chassis connector and number 12 or larger wire scraps. Solder the vertical element to the center conductor and attach the radials with nuts and bolts to the four corners, then solder each corner. Make the vertical element a bit longer than calculated and bend the radials down 25 to 30 degrees a short distance from the connector flange. Then trim the vertical element (in small increments) for the minimum SWR at the low end of the band in which it will be used. When the SWR begins to go back up, it should be lowest near the center of the band. If not, trim carefully until it is. Then little by little bend the radials down until you get a 1 to 1 SWR. This will be between 30 to 45 degrees, as shown below.
Number 8 wire was used. Ends were hammered flat, filed to shape and drilled. A small propane torch, used carefully so as not to overheat the connector, will make the soldering easy. Flux paste on the connector's flange will aid solder bonding. The vertical element's end was filed down until it fit inside the center pin connector. Waterproof the coax connector so water cannot seep into your coax.
Old weathered, corroded junked ham beams are another excellent source of recyclable antenna materials. I salvaged an old phased pair of inoperative Cushcraft two meter beams that were covered with corrosion and rust and were destined for the trash dump. Removing the rusted and corroded hardware was easy after a brisk wire brushing and soaking all the hardware with WD-40 (a penetrating oil) over night. After disassembling all the aluminum elements from the boom, I gave the boom and elements a good soaking and brushing in an acid bath. Acid solutions made specially for cleaning aluminum are available in well-stocked hardware stores. I now had clean looking elements and booms. A little time sanding out the corrosion pits with fine wet sandpaper and the elements and boom were as good as new.
I then drilled pilot holes on one boom 90 degrees and about an inch (2.5 cm) from the existing element holes. Upsizing the pilot holes to the diameter of the elements and securing all the elements with new sheet metal screws one size larger than the original size (so these new screws were tight in the old holes) tied them all together.