Amateur Satellites

Basics

Amateur satellites are like tiny repeaters in the sky. Some support voice operations (FM and SSB), some support Morse Code and some support packet operations. They are really small, smaller than a shoebox and have a couple of radios a battery and few small olar cells. Thye usually receive on one band and transmit on the another band. Most of the currently orbiting satellites use VHF and UHF, which makes it convenient to use the VHF/UHF radios we already have. To learn more you can visit amsat.org later.

ORBITS: Most Amateur satellites revolve around the earth in a Low Earth Orbit (LEO) and pass over different parts of the earth at different times. We can use them when they pass over our location and a pass lasts from about 7 to 12 minutes. When they rise above our horizon, it is called AOS (Acquisition of Signal), and when they set below the horizon it is called LOS (Loss of Signal). It is like Sunrise and Sunset but they don't always rise in the East and set in the West. Each pass is different, so the passes are indicated by AOS Azimuth and LOS Azimuth. One more thing, the passes have different elevations, but as long as the pass is over our location we can use the satellites unless something like a mountain or building ar trees get in the way.

FOOT PRINT: Since they operate like little repeaters, very long distance contacts can be made via satellites. To understand this, just shine a flash-light on the floor. The circular area where the light touches is called the Foot Print. A typical foot print of an amateur satellite is as wide as the size of USA and everyone within the foot print can use the satellite to contact others in the foot print. To add to that, the foot print is moving, so people is US, Canada and Mexico can contact each other.

Operating Technique

FM amateur satellites are the easiest to work with. In fact, the newer satellites can be worked with just Handheld radios. Since HTs do not support SSB and CW modes, working with SSB and CW satellites requires portable or desktop radios that can operate on the VHF and UHF satellite frequencies.

DOPPLER CORRECTIONS: Since the LEO satellites move at great speeds, the frequency changes a little at the receiver. This change happens at both the satellite as well as the operator (you). This is called Doppler Shift and it affects the higher frequency more than the lower frequency. To compensate for this one of us, either the satellite or you, have to change their frequency. However since the satellite cannot change, we have to change both our receiver as well as our transmit frequencies.

FM SATELLITES: Working with FM satellites is simpler. The change in VHF is relatively small and we do not need to change it during the pass. The change in UHF frequencies is a bit more but we need to change it only a few minutes. Fortunately, most FM radios have memories that we can use to store the frequencies in 5KHz steps, then we just have to change the memory channel every few minutes or so.

Here are a few recordings of some of the passes Link to Recordings

Pass Predictions

AMSAT.ORG provides a page to list the passes of any satellite over your location. Location is to entered as a Grid Square or as Lat/Long of your location. Here is a convenient interactive Grid Square map.

The Calendar below indicates a short list of "workable" satellite passes over Fremont Callifornia. Workable is defined as having an elevation of 10 degree or more and between 9am to 10m. The "Agenda" view provides a linear easy-to-see list. Thanks to Google Calendar for providing this option.

Hopefully this will get you interested and enjoy working with amateur satelliyes. If you have any questions, please do not hesitate to ask via our Contact Us page.