Summer 2007 Issue

SATELLITES

Satellite Station Alternatives

By Keith Pugh, W5IU

Since my last column, I have participated in three major amateur radio events: the Dayton Hamvention®, Ham-Com, and Field Day. This year at the Hamvention® and Ham-Com I had the opportunity to be in charge of real-time demonstrations on the amateur radio satellites. In the past I have usually done these demonstrations utilizing only the FM satellites or given a “receive only” demo on the SSB/CW birds. Working with Drew Glasbrenner, KO4MA, last year inspired me to include full demonstrations of the SSB/CW birds.

This year I was determined to find a way to do full demos on all of the birds. In addition to requiring multi-mode transceiver capability, SSB/CW demos require more “hands-on” operation to do the precise tuning required to compensate for Doppler and match up your uplink and downlink while still keeping the antenna pointed, etc. The RF environment at hamfests and major conventions represents a challenge as well. In this column I will address some solutions to these demo problems and expand into Field Day with a special mode this year.

Multi-mode Satellite Demonstrations

Demos on the FM birds are usually done with little more than a dual-band HT and an Arrow antenna or its equivalent. Only one uplink-downlink pair is used per transponder, and Doppler tuning in 5 -kHz steps of the higher frequency is adequate for the mode V/U and U/V birds. A full-duplex capability is highly desirable so that you know for sure when you are “making the bird,” but it is not absolutely necessary. One hand can be used to control the antenna and the other hand the channelized FM radio.

On the SSB/CW birds, full-duplex operation is absolutely essential, and precise tuning of both the uplink and downlink is necessary to locate the station you wish to talk to, match up the uplink to the downlink, and continue to correct for Doppler. This normally requires two independent radios, since most full-capability satellite radios are usually a bit cumbersome for a portable environment. All of this must be done while keeping the antenna(s) pointed at the bird. Most people come up at least “one hand short” to do all of this without some extra help.

Handheld multi-mode receivers such as the ICOM IC-R20, Yaesu VR-500, and Kenwood TH-F6A are available; however, these radios suffer, to varying degrees, from poor sensitivity, wide-open front ends, and marginal detectors. Some of these problems can be tolerated in a benign RF environment, but not at Dayton. None of the current handheld equipment has a SSB/CW transmit capability. The best compromise I have found is the Yaesu FT-817 Back-Pack Radio. At least one of these is necessary for the transmit capability. The FT-817 can be paired with one of the other receivers mentioned above, or better yet, with another FT-817. Many other combinations are also possible with larger, more powerful radios, but for the purpose of this discussion I have chosen two FT-817s as the smallest combination of radios that will provide acceptable uplink and downlink performance to do the job.

Two possibilities have been explored for the antenna control problem. First, assign the task to another person. Second, place the antenna(s) on an AZ-EL positioner so that the antenna(s) do not have to be held constantly—only updated periodically. Both methods work, and the second method works better if a second person is assigned that task as well.

W5IU at the Dayton Hamvention® demo area working AO-51 FM. The WA5VJB Cheap LEO Antennas and W5IU Cheap AZ-EL Positioner are in the background. (Photo courtesy of Bill
Reischl, KBØAZB)

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