A Portable Reflector S-Band (APRS) Antenna Bob Bruninga, WB4APR This APRS Antenna (sorry, I couldn't resist the name) is designed to be a portable lightweight communications antenna for the traveler who needs ready access to worldwide satellite voice communications via AO-40. It is not designed to be a permanent outdoors antenna system suitable for all weather conditions. It uses mixed metals and non weather proof motor positioning controls. But beyond these limitations, it is a neat, foldable (much assembly required) 1 meter antenna system including a tripod and remote control motor system that will fit in a normal suitcase (24" long). Or the dish can be trimmed to 21" panels to fit in any industry standard suitcase. The Reflector System is based on the foldable vegetable spreader concept of 16 wedges deployed around a central hub and held in place by a web of radial spokes. An F/D ratio of .3 was chosen for the best match to the readily available AIDC 3033 and other simple dipole feed systems. Using an unmodified AIDC converter (but with the 1/4 wave stub filter removed), the dish provides a measured 11 dB SNR on the middle beacon. Making the filter mods improves this to 14 dB SNR or better. The portable mount and remote control system takes advantage of the near zero inclination of the AO-40 orbit by using a polar mount. With this mount, not only is almost all tracking movement done with just one motor, but also alignment is trivial. The polar mount has the primary axis of rotation aligned with the earths polar axis. Thus with the 2 degree inclination of AO-40, the antenna is never more than 4 degrees or so off of the satellite in the up/down direction. Since this is within the beamwidth of the antenna, you can always find AO-40 by just setting the up/down tweaking motor to center and moving the antenna about the polar axis until you find the beacon. From then on, you can track AO-40 for hours with only occassional bumps of the polar motor. Alignment only requires pointing the front leg of the mount towards south and then lengthening or shortening the legs to achieve a tilt angle for the polar axis that equals your station's latitude. The APRS Antenna was designed entirely of readily available Home Depot plumbing and electrical fittings and parts. The total cost of these parts is less than $xx. The two electrical screwdrivers used for the drive system add an additional $20 each to the overall system. Since the APRS antenna was designed only for portable operation, the remote control seems a little bit of a luxury when your operations will usually be done from the parking lot anyway. But remembering how cold the parking lot at an AMSAT convention in Maine can be, I decided the added cost of the screwdrivers was small compared to the creature comforts of working AO-40 from the hotel lobby instead of the freezing termperatures outside. Also the screwdrivers help with ballast to balance the antenna, and since the extra weight is required anyway, it may as well be functional. One advantage of the S-Band downconverter at the antenna is that the coax run can be over 100 feet of commmon RG-59 coax cable. This is why it seems very practical to add the remote motor control for convenient operation indoors. To date, I have not focused too much on the uplink since there is nothing unique about transmitting on UHF. But I hope to make a 6 element UHF addition to the feed system so that the dish can be used as a reflector as well. ASSEMBLY: Extreme care should be taken to align parts in exactly 90 or 45 degree angles true to each other. If you follow these steps in sequence, the mounting system should go together quite well. If anything has to be forced, you can re-heat some solder joints to relieve stress. Initial Assembly Preparations: First solder all parts that need no mutual alignmnet into fixed solid Pieces as follows: 1) Solder the N1, N2 and N3 parts into the North Yoke Piece 2) Solder the B3, B4, B5, B6 and B7 pieces into the Base Unit Piece 3) Solder the S1, S2, S3 south leg Piece 4) Solder the S4, S5, S6 Polar Axle Piece 5) Solder the S7, S8, S9 center brace Piece 6) Solder the P6 and P7 side bracket Pieces Unit Alignment Assembly: Assemble the pieces temporarily using tape at all removable junctions so that final alignment can be obtained prior to final soldering of the N5 and N6 street elbows and drilling of pilot holes for all assembly clips. 1) Add the N4 pipes to the North Yoke Piece and tape in place. 2) Add the N5 elbows in the same plane as the N4 pipes. 2) Add the N6 elbows not in yoke plane, but in the vertical plane. 3) Add and tape the two N7 "T"'s and N8 cross pipe to each other 4) Add the two B1 vertical "T"'s and tape to the two B2 pipes 5) Tape the two B2 pipes to the Base Unit Piece. 6) Add and tape the south Leg Piece 7) Add and tape the Center Brace Piece 8) Add and tape the Polar Axle Piece to complete the structure. 9) Now solder the N4, N5 and N6 pieces together into two diagonal pieces. 10) Now solder the two N7 and two B1 "T"'s into two leg pieces. Parts list: ----------- North Yoke: N1 - 5.75" Cu pipe N2 - "T" N3 - Two 45 degree street elbows N4 - two 18" Cu pipes N5 - two 45 degree street elbows N6 - two 45 degree street elbows N7 - Two Cu "T"'s N8 - 27.5" Cu cross pipe Base Yoke: B1 - Two Cu "T"'s B2 - Two 18" Cu pipes B3 - Two 45 degree street elbows B4 - Cu "T" B5 - 1" splice piece B6 - Vertical "T" B7 - 12.5" Cu south brace South Leg: S1 - Cu "T" S2 - 4" Vertical pipe S3 - 45 degree elbow S4 - 12" Cu Polar pipe S5 - "T" S6 - 6" Cu polar bearing pipe S7 - 5.25" Angle center brace S8 - 45 degree elbow S9 - 8" Vertical brace Polar Bearing Structure: P1 - Bearing "T" P2 - 1.5" bearing extension pipe P3 - Bearing cross "T" P4 - two 1" splice pieces P5 - two bracket "T"'s cut 1/8th inch short on top end P6 - two 90 degree street elbows cut 1/8th inch short P7 - two 7.5" side brackets P8 - 3 hole cast aluminum conduit box Declination Mount D1 - 6" strap hinge D2 - 1/2" conduit set screw connector D3 - hand made nut holder D4 - 4" threaded 1/4" x 20 bolt D5 - Spring D6 - Declination hand crank piece D7 - Hand crank nut D8 - Hand crank bolt 2.5 inch 1/4" x 20 bolt and nut Dish Panels These are formed from a thin piece of Aluminum into panels that are 24" long and taper on the sides. I hope to be able to make these available from a local sheet metal bender... de WB4APR, Bob