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Amateur Radio Info & Exams - Space Communications

Space Stations

That thing where people say this or that "isn't rocket science". Well, for Amateur Radio, that isn't always true. Hams are permitted to not only engage in communications with space stations, that is with astronauts and cosmonauts, but if fortunate enough to become one, to communicate from space on a range of amateur bands, or sub-bands.

Parts 97.207 to 97.211 deal with space related operations. Not in the exam, but permitted frequencies are selected whole upper HF and microwave bands from 17 metres, and shorter; and sub-bands in some others. The latter include 144-146 MHz, and 435-438 MHz. This is due to the 2 metre bands being restricted to this segment in Region 1, and the 70 cm segment is restricted for similar reasons. The 70 cm portion also avoids parts of the band used for things like terrestrial repeaters.

The ISS is roughly 200 km above the earth, and thus its orbit means it moves relative the earth. Many Amateur satellites, like weather satellites, Iridium (mobile 'phone), and GPS / Glonass / Galileo positioning "birds" are in Low Earth Orbiting (LEO). For polar, or near polar orbits, the satellite passes north to south, or south to north (descending or ascending passes). There may be two or three visible passes, 90 minutes apart, in one direction, then some hours later, after the earth has turned, passes in the other direction. GNSS "constellations" have around 24 birds each, with several in each of a number of orbits, so there are generally always enough visible to provide a good "fix".

If you are sailing in the vast Southern Ocean, the ISS astronauts passing overhead can be the closest other humans to you at times!

Chris Hatfield using a Kenwood radio

This image shows Canadian Astronaut Chris Hatfield aboard the International Space Station, taking part in the ARISS - Amateur Radio on the International Space Station - programme.


Unmanned space vehicles are termed satellites, or "artificial satellites", to differentiate them from the Moon, and any other, much smaller, natural objects, and temporarily captured objects. There is also a natural object, 3753 Cruithne, which is following a similar solar orbit to us, which gives the appearance of being in earth orbit at times. I suppose it is just dancing with us! 2010 TK7 is also in a nearby solar orbit.

Amateurs can transmit to space, provided they are allowed to transmit on the UPLINK frequency. It is acceptable if your signal are retransmitted from space on a frequency outside you permitted frequencies. At times fairly conventional cross-band FM repeaters orbit on manned or unmanned space vehicles. These may need a CTCSS tone. The alternative is a "translator", which is a linear device, which might receive a section of 2 metres, and retransmit this at 21 MHz. Being linear, it can handle modes such as SSB, CW, some data or image modes, etc. It is thus possible for several earth stations (us earth-bound hams) to operate using different frequencies in its pass-band.

The examiner is however interested in "U/V mode, where the use transmits (uplinks) on 70 cm, and listemns (downlinks) on 2 metres.

These are solar powered, these cells charging a battery, which powers the equipment. In some cases, the batteries have died, so the satellite only works when in sunlight. Decades ago AMSAT-OSCAR 7 went silent, as the battery shorted; with further corrosion this has become open circuit, and it has come back to life, whilst in the sun!

A full list of mode designators, meaning bands and frequencies, can be read here: https://www.pe0sat.vgnet.nl/satellite/sat-information/modes/

Information, with a useful video can be found on the AMSAT-UK site, here: https://amsat-uk.org/beginners/how-to-work-ssb-satellites/

Doppler Shift

If you have been standing by the road, and an emergency vehicle has gone by with its siren blaring, you may have noticed that it has a high note while approaching, neutral as it passes, and a lower note while departing. This is due to the waveform being compressed in time approaching, and expanded while going away, hence the higher and lower perceived frequency.

While driving to or away from a repeater causes no significant frequency change, the high speeds of low-earth orbiting (LEO) satellites, which appear to move relative to our earth station, do cause this shift. Further reading on the topic will suggest storing around 5 pairs of channels, so you can select a high pair as the satellite rises (Acquisition-of-Signal), less high on as it climbs, a zero offset at its high point, moving down as it descents, and lower again close to Loss-of-Signal, as it goes below the horizon. An example is the ISS, which at times operates with 437.80 MHz uplink, and 145.800 MHz down. Some larger radios may have automatic correction of the uplink based on downlink tuning, and/or can be controlled by the software below.

Do I need a dish?

This depends on the band, and other factors, but generally NO. A short yagi, or similar directional antenna, pointed at the satellite can be useful. A lightweight yagis with a single boom, and crossed 2m and 70cm elements made from material such as portions of a metal tape-measure blade, or from arrow shafts can be pointed by hand. Rotating the antenna, that is, changing its polarity, may help too. In any case, dishes have low gain at 437 MHz, even if they are several metres in diameter, and even less at 145 MHz.

There are several designs which work well when the satellite is in any part of the sky, including overhead, such as the "turnstile". These have the benefit of working without an aiming system.

Even a handheld radio may be suitable for the FM satellites.

When will the satellite be visible?

It is possible to predict the motion of satellites using the maths developed by Johannes Kepler, in what is now Germany. These are the "laws of planetary motion". Software is available to calculate passes using Keplerian elements, also called Two Line Elements. Tracking programmes can also be used to control elevation and azimuth (El-Az) antenna rotators, azimuth being the compass bearing relative to true North, and elevation the angle above the horizon. The programs or apps typically display the track of the satellites over a map. Websites, such as Heavens Above also provide pass information.

LEO satellites typically only visible over a diameter of a few thousands of kilometres, but a good pass might allow contacts between eastern Australia and New Zealand. A clever implementation is however not for voice, but data, where a number of packet messages (like emails) can be uploaded to the satellite in Australia, then, typically under an hour later, downloaded whilst over France (or between a disaster zone in Africa, and the rest of the world) - clever for something invented before the widespread availability of the Internet, or mobile telephony in even the most deprived parts of the world.

As an aside, all orbits are elliptical, although for some this is very close to circular, such as that of the earth around the sun. Many LEO satellites are close enough to circular too. A special orbit occurs much higher, at 35,786 km above the equator. Here the orbit period is 23 hours, 56 minute, 4 seconds matching that of the earth (it then takes another ~4 minutes to align with the sun). This geo-stationary, or "earth synchronous" orbit allows dishes to point in a constant direction, and deliver things such as TV, audio, and high-latency Internet connections, using channels typically in the 3-4 GHz, or 12 GHz bands. As at high latitudes birds above the equator are very close to the horizon, the Soviets used satellites in a highly elliptical "Molniya" orbit, so it is visible for 8+ hours while climbing and descending, before zipping around the earth at lower altitude.

And lots of power?

I need to use lots of power so my signal has to get all the way into space, right? NO!!!, the signal path is line-of-sight, so little power is needed. More importantly, linear translators have an AGC = Automatic Gain Control, so if other users are using a few watts, and you start using a hundred or more, then you will turn down the sensitivity of the receive section, so the other users will no longer access the transponder.

The question on this references 97.313, alluding to clause (a) which states:

  An amateur station must use the minimum transmitter power necessary to carry out the desired communications.

Monitoring your signal on the downlink, where possible, is a good idea. This allows you to assess the relative strength of the returned signal and the telemetry signal.

At one point there was a geostationary Amateur satellite, and even for this, as 36,000 km+ range, not a lot of power was needed. The military use VHF or UHF transceivers on various military birds and as secondary payloads on commercial ones, to communicate with soldiers using only hand-held or man-pack radios, on ~200 MHz or ~400 MHz.

Satellite Beacons

Many "birds" include a transmission which may constantly transmit data about the satellite (telemetry), which can act as a beacon for stations wishing to manually point their antenna at it. These can be quite easy to hear, using either a hand-held or home/mobile (CW/SSB capable radio) on 2 metres; or an HF radio, depending on the band. If you use FM or AM, and it is sending Morse, you will just hear the natural noise quietening with each dit or dah; in CW (or SSB, or a radio with a BFO), you will here these as the familiar tones.


AMSAT is the association which co-ordinates various aspects of Amateur Satellite operations. However, membership is not required to use these devices. See: amsat.org

One of the distractors talks about Satellite Certification. This relates to commercial or marine licences only.


Beyond the scope of this section, it is also possible to bounce signals off the moon, termed "EME", for Earth-Moon-Earth, or Moonbounce. Using CW, or for the "super-stations", SSB, even for a large power, and using high gain antennas (arrays of multiple yagis), the received signal is weak, and requires amplification by "low noise" amplifiers. Certain recent weak signal digital modes may be used. Bands used are 2 metres to microwaves.

Relevant Questions

These are actual exam questions, from the published NCVEC Technician pool.

The 2018 pool moved regulations related questions to the T1 Regulations sections..

What telemetry information is typically transmitted by satellite beacons?
A. The signal strength of received signals
B. Time of day accurate to plus or minus 1/10 second
C. Health and status of the satellite
D. All of these choices are correct

It is the health (such as battery levels) and operating status of the bird, answer C.

What is the impact of using too much effective radiated power on a satellite uplink?
A. Possibility of commanding the satellite to an improper mode
B. Blocking access by other users
C. Overloading the satellite batteries
D. Possibility of rebooting the satellite control computer

This can block access to satellite for other users, answer B.

Most satellites are not a simple FM repeater, but rather use a linear translator. These receive in a segment on one band, and retransmit it on another band. Several users can transmit on marginally different frequencies, and be downlinked to different frequencies, so that several contacts can take place at the same time. Modes used include SSB, CW, and data, although sometimes there are FM weekends. Too much power will cause the Automatic Gain Control (AGC) to reduce the reciever gain, affecting other users.

Which of the following are provided by satellite tracking programs?
A. Maps showing the real-time position of the satellite track over the earth
B. The time, azimuth, and elevation of the start, maximum altitude, and end of a pass
C. The apparent frequency of the satellite transmission, including effects of Doppler shift
D. All of these answers are correct

Typically, these programmes display a map; the time and pointing details of the pass; and frequency details, accounting for the Doppler shift, so All, answer D.

What mode of transmission is commonly used by amateur radio satellites?
C. CW/data
D. All of these choices are correct

All these are used, depending on the satellite, and answer D.

Modes may also vary according to a schedule announced by the satellite managers.

What is a satellite beacon?
A. The primary transmit antenna on the satellite
B. An indicator light that that shows where to point your antenna
C. A reflective surface on the satellite
D. A transmission from a space station that contains status information

The beacons sends information about the satellite, and assists people tuning in the satellite, answer D.

Some are reflective, allowing the them to be visible as a moving star at night, while Iridium 'phone satellites are very shiny, so generate brief "flares" when they reflect the sun, even in the daytime. None deliberately emit visible light, although some military birds use lasers to communicate.

Which of the following are inputs to a satellite tracking program?
A. The satellite transmitted power
B. The Keplerian elements
C. The last observed time of zero Doppler shift
D. All of these answers are correct

"Keps", or Keplerian elements are the data used by tracking software to calculate the motion of the satellite, answer B.

With regard to satellite communications, what is Doppler shift?
A. A change in the satellite orbit
B. A mode where the satellite receives signals on one band and transmits on another
C. An observed change in signal frequency caused by relative motion between the satellite and the Earth station
D. A special digital communications mode for some satellites

Doppler shift is the apparent shift in frequency caused by the motion between the satellite and the earth station, answer C.

You may have heard of doppler radar, used to measure the speed (motion) of vehicles, for revenue raising purposes; and of balls in sport.

What is meant by the statement that a satellite is operating in mode U/V?
A. The satellite uplink is in the 15 meter band and the downlink is in the 10 meter band
B. The satellite uplink is in the 70 cm band and the downlink is in the 2 meter band
C. The satellite operates using ultraviolet frequencies
D. The satellite frequencies are usually variable

One must assume U stands for UHF, and V for VHF; with 70cm, and 2m being the most popular of these bands. Answer B.

What causes spin fading of satellite signals?
A. Circular polarized noise interference radiated from the sun
B. Rotation of the satellite and its antennas
C. Doppler shift of the received signal
D. Interfering signals within the satellite uplink band

You will remember that signals which are not of the same polarisation as the receive antenna are received poorly, so as the satellite, and its antennas rotate, the signal will fade in and out, or at least weaken considerable, answer B.

Fading also occurs if a simple whip antenna is oriented such that it is end-on the the earth station.

What is a LEO satellite?
A. A sun synchronous satellite
B. A highly elliptical orbit satellite
C. A satellite in low energy operation mode
D. A satellite in low earth orbit

Most (if now all) Amateur birds are in Low Earth Orbit, answer D. A fair few are in a polar, or near polar orbit.

Who may receive telemetry from a space station?
A. Anyone
B. A licensed radio amateur with a transmitter equipped for interrogating the satellite
C. A licensed radio amateur who has been certified by the protocol developer
D. A licensed radio amateur who has registered for an access code from AMSAT

Anyone, whether licensed or not, can receive the signal, answer A.

Which of the following is a good way to judge whether your uplink power is neither too low nor too high?
A. Check your signal strength report in the telemetry data
B. Listen for distortion on your downlink signal
C. Your signal strength on the downlink should be about the same as the beacon
D. All of these choices are correct

It is answer C.

On to: Operating Part 1

You can find links to lots more on the Learning Material page.

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Written by Julian Sortland, VK2YJS & AG6LE, February 2022.

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