Technical Articles

Satellite Basics (Part 1): Guide to Ham Radio Satellite Operating

One of the great things about Ham Radio is the endless ways you can enjoy the hobby. If you feel your Ham Radio enjoyment needs a shake-up, or you’re new and looking for interesting ways to get more involved, check out satellite operating.  There are over two dozen ham radio satellites in orbit right now, and they allow short QSOs over a few thousand miles to take place! Several satellites use FM, while others use SSB or CW, and a few more use digital modes.

Satellite operating is inviting for several reasons:

  1. You can get started with very simple gear.
  2. Most satellites are accessible by Technician-class licensees.
  3. Satellite passes are 100% predictable in advance and last only 15-20 minutes at most.
  4. They aren’t affected by the ups and downs of propagation like the HF bands are.

What You Need to Get Started

To make QSOs via satellite, you will need to be able to transmit and receive on both 2 meters and 70 centimeters. For the FM satellites, this can be as simple as a dual-band HT, or two separate HTs.  You will also need an effective antenna for satellite work, and a way to track satellites as they pass overhead.  You’ll also need a diplexer, which isolates your transmitted signal from your receive radio. Without it, you will overload the front end of your receive radio, making QSOs impossible. Several manufacturers offer diplexers. If this sounds like a lot to take on, it’s nowhere as difficult to get on the FM satellites as you would think!

FM satellites function like an orbiting repeater; only one person can access the satellite at a time. You transmit, or uplink, on one band and receive, or downlink, on another. For example, to use the popular FM satellite SO-50, you transmit on 2 meters and receive on 70 centimeters. Other satellites are the opposite, transmitting on 70 centimeters and receiving on 2 meters. FM satellites will require you to have a CTCSS (PL) tone on your transmit signal.

Satellites transmit with very little power, often less than one watt. However, this is more than enough for you to hear them, because they are line of sight. And when they’re right overhead, there (hopefully) aren’t any obstacles in your way! While some have been able to hear and make QSOs through satellites using mobile whip antennas, you will have better success by using small directional antennas; two commercial options are the Arrow dual-band handheld Yagi, which has 3 elements on 2 meters and 7 elements on 70 centimeters, or the Elk 5-element handheld log periodic antenna. The Arrow has an optional built-in diplexer, while the Elk doesn’t need one if you’re using a single radio. You can also build your own to get started; check out this article on cheap and easy Yagi satellite antennas.

Lastly, you have to be able to track when a satellite is going to be overhead. Generally speaking, you can only hear a satellite when it is above your local horizon. Some passes will only be a few degrees above your horizon, while others may go directly overhead. Every pass is different. Most satellites pass overhead about 5-6 times a day, and you need to be able to point your antenna at them as they move across the sky. The AMSAT website has a pass predictor on their site, or you can check out the site N2YO.com for pass predictions. There are also smart phone apps that track satellites as well. iPhone users can check out GoSatWatch (not free, but very good), or SatSat (free, but not as many features). Android users can check out AMSATDroid or Heavens-Above.

The position, in degrees, that the satellite first appears above the horizon is called Acquisition of Signal, or AOS. The position the satellite goes back down below the horizon is called Loss of Signal, or LOS.  A common stumbling block for new satellite users is remembering that you need to keep pointing your antenna toward the satellite, not the station you are contacting.

Satellites and the Doppler Effect

Because the satellite is transmitting a signal as it moves across the sky, you will have to work around the Doppler Effect. It’s Just like a train whistle that changes pitch as it passes you. Doppler is more noticeable on 70 centimeters than 2 meters; if the satellite you’re trying to work has a 70 cm uplink, you will have to adjust your transmit frequency as it passes overhead. If it has a 70 cm downlink, you will have to adjust your receive frequency throughout the pass. An easy way to do this is to program a series of frequencies in your radio’s memory and toggle the memory channels throughout the pass.

First Steps in Satellites

As with trying anything new, it’s best to take small steps as you learn. Here’s a simple exercise to help you get started: listening for the AO-91 FM satellite.

  1. Go to AMSAT or N2YO.com, or download one of the satellite tracking apps mentioned earlier, and get the latest pass information on the FM satellite AO-91 (also known as Fox-1B). AO-91 has a downlink frequency of 145.960 MHz, so it won’t be as affected by Doppler as other satellites.
  2. Use your current 2 meter radio and hook it up to the best antenna you have. If you’re trying this from your car with a mobile whip, try and go to a park or other area with as clear a horizon as possible. If you have a directional antenna, you will have to rotate your antenna to follow the satellite across the sky as it goes overhead.
  3. At AOS, open the squelch on your radio so you can hear static all the time. Start listening for signals through the static. With luck and experience, you will soon hear signals coming through the static as the pass progresses, until the pass is over.
  4. Try several different passes at different elevations above the horizon.

I’ll cover making contacts through FM satellites in an upcoming blog. Until then, keep listening for the satellites! Check out the web site of AMSAT, the Radio Amateurs Satellite Corporation, for news and more operating tips. Be sure to visit their booth at Hamvention this year, too!

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