Summer 2009 Issue

Satellites

Working the “Easy Sats” with Portable Equipment: An Update

By Keith Pugh, W5IU

The simplest satellite radio is a dual-band HT.

 

Over the years writing for CQ VHF I have touched on equipment to work the “Easy Sats” several times. However, I believe it is time to summarize this information and provide information on some new options that are now available. I will first discuss the basic modes of operation, and then the radios, and last the antennas.

The Basic Modes of Operation

The FM satellites are perhaps the easiest satellites to work and require less, simpler equipment. Current popular FM satellites are AO-51, AO-27, SO-50, and the ISS (International Space Station). These satellites are channelized and have one or two channels per satellite. The satellites are crowded and can only accommodate one QSO per channel at a time. Consequently, QSOs are quite short (typically call and grid square only) and timing of a call is everything.

There are multiple uplink and downlink pairs on AO-51 and the ISS that are scheduled for operation one or two at a time. With a couple of minor exceptions, all operation is in FM mode. Doppler correction is much simpler due to the bandwidth of the FM equipment and the FM capture effect. Uplinks or downlinks above 2 meters must be Doppler corrected, but it can be done in as much as 5-kHz steps. You can get by without Doppler correction for 2 meters and below. Full-duplex operation is desirable, but not absolutely necessary. With full-duplex operation, you know you are “making the bird,” since you can hear yourself on the downlink. This is good, unless you have no way of preventing feedback of the downlink audio into the uplink. Headphones will prevent this feedback, or careful placement of the speaker and adjustment of downlink audio level will minimize it. For demonstrations, I find using a half-duplex radio, such as the Yaesu FT-817, is very satisfactory.

For the SSB/CW satellites, it is essential to operate full duplex so that you can hear yourself and keep Doppler precisely under control. Current popular SSB/ CW satellites are AO-07, FO-29, and VO-52. These satellites have linear transponders with at least a 50-kHz wide passband. Several QSOs can simultaneously take place within the passband and a good, old-fashioned “rag chew” is possible and encouraged.

Full-duplex operation is essential so that you can keep the narrower uplink and downlink signals on the same frequency by hearing yourself and the other stations on the downlink at the same time. Computer control of the uplink and downlink is nice, but not essential. One exception to the full-duplex rule is possible if you do have computer control of the radio. However, I find this less than satisfactory. Operation is typically done using a full-duplex radio or two half-duplex radios. For demos, I typically use two Yaesu FT-817s and find them very satisfactory. Many other combinations are possible and will be discussed under “Radios” below.

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