My favorite ham activity is making contacts via satellites. Not only is there the romantic notion of sending messages into outer space, but you have to trace the orbit of the satellite with your antenna while tuning the radio, to compensate for the Doppler effect.
The satellites AO-51, SO-50, and AO-27 orbit the Earth acting as repeaters. Repeaters are automated relay stations that allow hams to send signals over a greater distance using low-power hand held transceivers. The satellites allow hams to relay messages from Earth to space and back to other hams somewhere on the planet. The International Space Station (ISS) also has a repeater, but occasionally, if you’re lucky, the astronauts turn on their radios to make contact directly with hams on the ground.
The following instructions will get you started listening to birds (satellites) on FM, which can be done with a simple VHF/UHF FM radio with a whip antenna, without the need of a ham license. For better coverage, you can use a Yagi antenna (like the one pictured above) connected to a mutli-mode radio and a license (if you want to transmit). A Yagi antenna can also be used to improve the signal of your hand held radio.
All you need is a VHF/UHF FM receiver (like a police scanner) or a VHF/UHF transceiver (like a Yaesu VX-7) and an antenna.
3. Reading the chart
This pass chart shows the Start (when/where the satellite enters on the horizon), the Max. Altitude (when/where the satellite is at its highest point in the sky), and the End (when/where the satellite finishes it’s pass). Alt. is the altitude, the angle of the satellite from the observer’s horizon. 0 degrees is exactly on the horizon, and 90 degrees is directly above the observer. Az. is the Azimuth, the cardinal direction of the satellite from the observer’s point of view.
4. Picking a good pass
Satellites orbit the Earth at all sorts of angles, some that are very close to the horizon and some that are directly overhead. It is much easier to hear a satellite that passes directly overhead. To find a good sat pass, check the Max. Altitude Alt. for a pass that is 45 or higher (the higher the better). In our example, the second pass at 7:28 looks like a good one since the Max. Altitude Alt. is 77. The first pass at 5:52 has a Max. Altitude Alt. of only 12 which is very close to the horizon and difficult to pick up.
5. Finding the frequency
Satellite repeaters work with two different frequencies, an uplink and a downlink. You will listen to signals received on the downlink. If you wish to transmit, you’ll need to program in the uplink frequency as well. Follow the corresponding links to find the FM repeater frequencies of the satellites. The frequencies often change, so be sure to check the websites for the latest updates. AO-51, SO-50, AO-27, ISS. Tune your radio to the downlink frequency and you’re ready to go outside and listen (example: 435.300 MHz FM).
6. Aiming a whip antenna
If you’re using a whip antenna, you will not aim the antenna directly at the satellite. Instead, you’ll keep it perpendicular to the satellite. You can rotate the antenna by rotating your wrist to try and get a clearer signal.
7. Following the pass with the antenna
You will trace the path of the satellite orbit with the antenna using the Heavens-Above pass chart as a guide. At the Start Time, start with the antenna perpendicular to the Az. direction at the given Alt. For example, at 7:28, aim the antenna perpendicular to north at 10 degrees above the horizon. Trace the path of the satellite so that at the Max. Altitude Time the antenna is pointed in the corresponding location. For example, at 7:33, the antenna should be perpendicular to west northwest at 77 decrees above the horizon. Finish tracing the path of the satellite so that at the End Time the antenna is perpendicular to the corresponding location. For example at 7:39, the antenna will be perpendicular to south southwest at 10 degrees above the horizon. It can be very difficult trying to catch the satellites and you may spend a lot of time not hearing anything. As you trace the general path of the satellite with the antenna, move the antenna around in small side to side and up and down motions until you hear a bit of audio. Adjust the antenna to make the audio clearer.
8. Tuning the radio for the Doppler effect
The Doppler effect makes the frequency vary by .010 MHz. As you trace the path of the satellite with the antenna, you will also need to tune the radio back and forth plus or minus .010 MHz until you hear a good signal. Early in the pass, you will add .010 MHz, for example, if you’re listening on 435.300 MHz, you’ll need to tune the radio back and forth between 435.300 MHz and 435.310 MHz. Later in the pass, you will subtract .010 MHz, for example, you will tune the radio back and forth between 435.300 MHz and 435.290 MHz.
Here is an audio clip from my first satellite contacts. The contacts seem to be going pretty slowly, but while I was making them, I remember everything happening very quickly. It was a lot to tune the radio and maneuver the antenna while trying to write down the call signs of the contacts.