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Table 1. 1987 A MSA T-OSCA H 10 attitude predictions.

Table 1. 1987 A MSA T-OSCA H 10 attitude predictions.

polarization is right- or left-handed. This circular polarization can be created using the crossed-yagi design by leedmg one of the yagis

90 degrees out of phase with the other. The sense is selected by switching a delay tine from one antenna to the other. Some of these antennas aiso use element staggering to achieve the circular pattern.

When purchasing a satellite antenna, you must consider several things. These include performance, price, and reliability. In most circumstances, you would consider more gain to be a deciding factor, but for satellite chasing, more is not always better A forty-foot dish has a lot of gain at 70 centimeters, but it would be quite a chore to keep up with a low-orbit satellite like Fuji-OSCAR 12 as it goes from horizon to horizon during a 20-minute pass.

This also holds true for large yagi arrays. They might be good for moonbounce. but they are very difficult to steer accurately and quickly for most satellite work. Although the inclusion of stainless-steel hardware increases the price, it does improve reliability.

Polarization-switching relays also add to the antenna cost, but provide more versatility for operation through satellites with different circular sense. I would suggest a two-meter crossed yagi with 14 to 22 elements and a 70-cm crossed yagi with 16 to 30 elements. Larger arrays with stacked antennas may be appropriate after you gain some experience.

For the antenna builder, there are many antenna types from which to choose. Several cross-yagi designs have been described in publications like the ARRL Handbook and the VHF-UHF Manual from the Radio Society of Great Britain.

A favorite home-brew antenna is the helix. It looks like a cork* screw with a reflector plate in the back. Building one for two meters is quite a chore, but for 70 cm it is a fine performer and not unwieldy. Due to excellent broadband characteristics, its dimensions do not require the same precision during construction as a yagi. Its only shortcoming is that it cannot be switched from one sense to the other. It is either wound for right-or left-hand polarization,

Other useful satellite antennas not typically found in catalogs include VHF and UHF quads and turnstiles. For two meters, the quad is not large and won't exhibit quite the signal-fading symptoms experienced by linear yagis pressed into satellite service. The turnstile is simply a crossed dipole suspended above a reflector to give a nearly omnidirectional horizontal pattern. More detaifed information on home-project satellite antennas can be found in Martin Davidoff s The Satellite Experimenter's Handbook..

Some Satellite-Station Setups

From the sound of it. amateur satellite chasing requires significant antenna arrays. Fortunately, ihis is not always the case. Although the nev.comer to space communications may find minimal systems unsatisfying the activities of some stations are very thought-provoking. Doug WB51RI has been monuonng FO-12 using a whip antenna n the garage with a Hamtronics pre-amp and downconverter to a Kenwood TS-120S Jody N5HOM has made several FO-12 QSOs using a Diamond XL-200 dual-band base-station anienna. a single run of 9913 coaxr a Yaesu AD-2 du-piexert and a Yaesu FT-726R transceiver with a two-meter power amplifier

Scott WA5LHM has been able to monitor AO-10 using a two-meter mobile antenna in ihe shack with a Kenwood TS-711A, Courtney N5BF has monitored his own signals through FO-12 using a quarter-wave "mag-mount" antenna En the attic for transmit on two meters and a rubber ducky on 70 cm for receive. The rigs were ICOM with a duck-mounted preamp.

Perhaps the most intriguing activities are those of Chris N5JHM. who has made mobile-in-motion QSOs via A0-10 from his pickup truck using a Kenwood TR-751A with 5/8-wave whip lor receive and an ICOM IC-471H with whip an tenna for transmit. These contacts were possible due to the antenna orientation of AO-1Q in recent weeks.

The challenge of satellite operation with simple setups can provide a very enjoyable pursuit similar to long-haul DX on the shortwave bands using milliwatt transmitters Come on up and pin the fun!

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