Health and status of the satellite is telemetry information typically transmitted by satellite beacons.

Some satellites may transmit other information, but the key word here is typical.

Memory tip: A satellite is passing by. Think of passing someone on the street "How are you?" "I'm good," or the like is about all you get. In a quick pass, you "typically" get their health and status.

Last edited by mlitty. Register to edit

Tags: section7.4

Most analog satellites have linear transponders that simultaneously retransmit multiple signals in a relatively large passband (e.g., 50-100kHz wide).

But to stay linear and avoid distortion, the transponder must retransmit its input with the same relative signal strengths. If one uplink signal is stronger than the others, it will get that much more of the satellite downlink power. The transponder might even have to reduce gain to stay under its maximum output power, further reducing the weaker signals.

Thus you should never transmit more power than you need to a linear transponder to avoid "blinding" it to signals from other users.

For more information, see the ARRL's An Amateur Satellite Primer

Last edited by karn@ka9q.net. Register to edit

Tags: section7.4

Satellite tracking programs tell you where a satellite is at a given time, including its altitude and where it will be at the start and end of a pass, relative to your location.

The tracking programs even tell you how much to change your transmitter's and receiver's frequency to compensate for the Doppler shift you get when the satellite is coming toward you or moving away from you.

So all of these answers are correct.

Last edited by kd7bbc. Register to edit

Tags: section7.4

Amateur Radio Satellites can operate in multiple modes of transmission.

In general, the modes are FM/CW/SSB/Digital/ SSTV/PSK31.

Last edited by kd7bbc. Register to edit

Tags: morse code section7.4

A beacon provides us with a gauge to determine how much power we should use. If you transmit your signal and compare it to the beacon strength, you can then adjust your power up or down to match the beacon. That would be the optimum transmitting power for your station. The next thing that the beacons provide us with is a schedule of the satellite's activity. It might tell you that it is on during a particular time period and off during others.

The beacon can also help us tune our radio to compensate for doppler shift. Since we know the beacon is supposed to be on a certain frequency, we can calculate where our signal will be based on the current reception of the beacon (http://www.amsat.org/articles/houston-net/beacons.html)

Last edited by n4adk. Register to edit

Tags: satellite operation definitions section7.4

Keplerian elements, named after Johannes Kepler (1571-1630) and his laws of planetary motion, are the parameters that define the orbit of a satellite. From these elements, a computer program can calculate the time and bearing of a satellite pass, relative to your position on the earth.

The weight of the satellite is not one of the Keplerian elements. The last observed time of zero Doppler shift would be the time that the satellite was moving neither toward you nor away from you (like when it was overhead, for example). While this might be interesting data, it isn't enough to predict where it will be coming from or going to on its next pass, or at what altitudes.

According to AMSAT's "Keplerian Elements Tutorial" the "basic orbital elements are":

1. Epoch
2. Orbital Inclination
3. Right Ascension of Ascending Node (R.A.A.N.)
4. Argument of Perigee
5. Eccentricity
6. Mean Motion
7. Mean Anomaly
8. Drag (optional)

Last edited by mk2019. Register to edit

Tags: section7.4

The most common references to the doppler effect (or doppler shift) refer to sound; one of the most common examples used in highschool science classes involves a fire engine (or other vehicle with a siren) whose siren seems to drop in pitch drastically when the vehicle passes you. The producer of the sound does not actually change frequency, but the relative speed of the vehicle producing the sound to the object (you) receiving the sound makes it seem to you that it does.

The same principle applies to a radio frequency signal; the relative motion between a satellite and the earth station can cause a shift in the frequency at which you can receive the signal depending on what its position and momentum are relative to the receiving station.

Last edited by kd7bbc. Register to edit

Tags: satellite operation frequencies section7.4

"mode U/V" is short for "mode UHF/VHF" -- meaning that the uplink is UHF, meaning 70 cm, and the downlink is VHF, meaning 2 meters. There are of course other UHF and VHF amateur bands, but those below 1 GHz are not available for amateur satellite operation.

Last edited by karn@ka9q.net. Register to edit

Tags: 70 cm 2 meter satellite operation section7.4

Satellites are not stationary in space; they are constantly moving, and generally they are rotating as well. As they turn, the antennas on the satellite change position relative to your location. The signal may fade if the antennas are directional, or even if omnidirectional, if they are obscured by the rest of the satellite.

This is referred to as "spin fading" because the fading is caused by the satellite spinning around.

Last edited by gavinmcg. Register to edit

Tags: propagation satellite operation antenna directional antenna

Just remember that we are talking about a satellite; this question could be a bit tricky if you haven't seen it before, but LEO refers to the position, not to any operation. It is, as the answer indicates, Low Earth Orbit.

Although a Low Earth Orbit is highly elliptical to escape the Earth's gravity at the low point (perigee), the question is asking what is the satellite, not what type of orbit is the satellite following.

Last edited by johnschubert. Register to edit

Tags: satellite operation section7.4

Yep, anyone who can receive the telemetry signal is allowed to receive telemetry from a space station but not allowed to transmit to one without a license.

With the availability of inexpensive RTL-SDR USB dongles, many people are trying their hand at receiving telemetry from space stations even if they don't have a license. For some of us, this sort of thing is what got us interested in amateur radio to begin with.

Last edited by rjstone. Register to edit

Tags: section7.4

The term uplink suggests that the question was written with amateur radio satellites in mind; most amateur radio satellites have what is called a linear transponder, which listens to a relatively large passband (perhaps 50-100kHz wide, where a normal SSB signal uses 3kHz or less) and retransmits it on another frequency (the downlink). In this way, multiple signals can be carried simultaneously by the satellite.

If your uplink power is too low, your signal coming back may not be strong enough to be heard; on the other hand, if your power is too high you could "blind" the satellite to other signals, blocking them from using it.

The satellite will constantly transmit a morse code (CW) beacon on the downlink; you can use that and compare it to your signal strength when it comes down. If your signal is stronger than the beacon then you are likely overloading the receiver and potentially blocking other users; if your signal is weaker than the beacon then the receiver isn't hearing you as strongly as it could. Adjust your power until the your signal strength on the downlink is the same as the beacon and you're in the "just right" zone =)

Last edited by qwerty 2.0. Register to edit

Tags: section7.4