Working FM Satellites

Post date: Oct 06, 2013 7:21:15 PM

The bad news: There aren't a lot of choices these days when it comes to working satellites on FM. AO-51 appears to be down for the count, and AO-27's hope for continued useful life is dwindling. The only fully-operational "repeater in the sky" as I write this is SO-50.

The good news: You can still have a lot of fun!

Background

The first Orbiting Satellite Carrying Amateur Radio, or OSCAR, was launched in 1961, a few years after Sputnik. Since then, well over 100 "birds" have been launched by the global Amateur community. Some function as FM repeaters, others have linear transponders so they can carry several SSB/CW or other modes simultaneously; some have packet nodes or digipeaters, and just about all provide some sort of telemetry transmissions. They come in all shapes and sizes, and you can hear many of their transmissions, even if you're not able to work another ham through them. Amateur satellites have a rich history, the research of which can itself be entertaining.

In addition to the traditional amateur satellites, since 1983, when W5LFL first took an HT on the space shuttle, there have been many opportunities to work astronauts or otherwise use amateur equipment aboard the ISS station and other craft.

Equipment needed

• • 1 dual-band FM HT

That's it! Yes, you can whip out your $30 Baofeng and work a satellite. (Also, two single-band radios could be used, one to transmit, one to receive.) To be sure, having a better antenna than the stock rubber duck will give you a stronger signal, either an omnidirectional with a little more gain, or even a hand-held dual-band Yagi made for the purpose. Also, a radio with a stronger transmitter and more sensitive receiver may help.

When to work it

Unlike TV satellites, which companies pay BIG bucks to reserve their little section of sky real estate so they can park their satellite over a particular region of the world, amateur satellites are NOT geostationary, but move around so that amateurs all over the world can use them. They are generally in Low Earth Orbits, or sometimes highly elongated orbits. While close to the earth, the satellites fly across the sky quickly, and have a limited range. When at the apogee of an elongated orbit, the satellite is high and slowly moving, covering a wide area for a longer time.

How do you know when you can work a satellite? Software, running either on your own computer (desktop or mobile) or on someone's web server, contains the calculations that tell when a particular satellite is going to be where. Heavens Above is a great resource for tracking all sorts of celestial objects, including the ISS and ham satellites, including SO-50. If you can see it, you can work it!

Programming your radio

You could just manually set your radio in VFO mode to 145.85 & 436.795 MHz (don't forget the PL tone!), but you'll do much better if you program a series of memories instead. Why a series? Doppler effect! As the satellite moves towards you rapidly, its operating frequency will raise significantly. Once it passes overhead and moves away from you, its frequencies will suddenly drop below the published numbers, just like the sound of a train passing by. Programming a series of 3-9 channels to include the official frequencies in the middle and both transmit and receive moved further away on either side will give you a choice of frequencies to use -- start off about where it should be, then keep switching to use whatever brings it in the best. Having more channels, spaced 2.5 or 5 kHz apart, give you maximum choice.

Aiming

Having the sky chart showing the pass you're going to try to use (and a watch!) will help you to know where to aim your antenna. (If you have a fancy computer-controlled telescope or other antenna mount, it could be programmed to track it precisely for you!) The Yagi is intuitively pointed at the satellite. With an omni-directional antenna, you don't want to point the tip up in the sky, but instead turn the radio so that the antenna is broadside to the satellite. Sweep the antenna back and forth in the approximate area and rotate it (to match polarization) to obtain the best signal. (This assumes, of course, that you're able to hear the satellite!) Another tip: Ditch the squelch; you'll often be able to hear the carrier signal quieting the background noise before you're able to hear anyone talking on it.

Courtesy & other tips

Unlike your local repeater, a satellite presents a somewhat more precious DX window, and your time available to work it is short. QSOs should be kept short during a busy pass to give others in your area a chance to make contact (though it is also kind of nice to listen to conversations more interesting than a signal report exchange!). Don't waste your time getting angry if things don't go exactly as planned; make the most of the opportunity and be assured that it will make another favorable pass in the future. Just as when you first got your license, it's a good idea to listen and get the idea of how things work before making your transmission. If it's esp. busy on your first pass, consider waiting until another pass to transmit, and enjoy a low-stress listening session -- hone your directional and frequency tracking skills without the extra burden of trying to establish a 2-way contact. But when you're ready and the coast is clear, don't be shy -- make your move!