T8B

Amateur satellites

Why a satellite's frequency shifts as it passes, how tracking works, and how to use uplinks, downlinks and beacons.

12 pool questions1 on the exam

Syllabus: Amateur satellite operation: Doppler shift, basic orbits, operating protocols, modulation mode selection, transmitter power considerations, telemetry, satellite tracking programs, beacons, uplink and downlink mode definitions, spin fading, definition of "LEO", setting uplink power

Approaching raises the frequency. Receding lowers it.

Doppler shift is a change in the frequency you receive, caused by relative motion between the satellite and you. Like a siren: higher pitch coming, lower going.

Same transmitter all the way. Only the motion changes what you receive.

Satellite positionapproaching

You receiveHigher

The shift is larger on higher frequencies. It is zero only at closest approach.

RememberDoppler = motion changes frequency. Spin fading = rotation changes strength.

Orbit numbers in, a pass plan out

LEO is Low Earth Orbit: close to Earth, about 100 minutes per lap. That is why a pass lasts only minutes.

Inputs describe the orbit. Outputs tell you when and where to point.

The input is the Keplerian elements: numbers that describe the orbit. A tracking program gives all three outputs: a live map, pass times with azimuth and elevation, and the Doppler-shifted frequency.

RememberKeplerian elements describe the orbit. Not the satellite's power, not Doppler history.

Uplink up on one band, downlink back on another

The uplink is you to the satellite. The downlink is satellite to you. U/V reads uplink first: U (70 cm) up, V (2 m) down.

Mode name = uplink band / downlink band.

Satellites use SSB, FM, and CW/data, so all of these are correct. On a linear transponder, shout too loud and you block other users. Aim your downlink to match the beacon.

Check your own downlink against the beacon. Too much uplink power blocks others.

RememberUse only enough power to match the beacon. More just crowds out everyone else.

A beacon broadcasts satellite health to anyone

A beacon is a transmission from the satellite carrying telemetry: the satellite's health and status (battery, temperature and so on). Anyone can receive it. Amateur satellite telemetry is not encrypted.

One-way broadcast. No key, no license needed to listen.

RememberBeacon = status broadcast. Telemetry = health and status. Anyone may listen.

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