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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 a few other much smaller natural objects. There is also a natural object 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!

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 manner 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.

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. At least one, decades ago 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!

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 is 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.

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, and the moon around the earth, although people do get over-excited about "super-moons", when the moon is at perigee while its illuminated surface is facing us, that is the full moon appears while it is at its closest to earth. 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, 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.

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.

T8B01 [97.301, 97.207(c)]
Who may be the control operator of a station communicating through an amateur satellite or space station?
A. Only an Amateur Extra Class operator
B. A General Class licensee or higher licensee who has a satellite operator certification
C. Only an Amateur Extra Class operator who is also an AMSAT member
D. Any amateur whose license privileges allow them to transmit on the satellite uplink frequency

Any amateur who may transmit on the on the satellite uplink frequency may use the bird. 97.207 allows communications with space stations, clause (c) specifying the bands and sub-bands permitted; 97.301 the bands for Amateur operation by licence class.

T8B02 [97.313]
How much transmitter power should be used on the uplink frequency of an amateur satellite or space station?
A. The maximum power of your transmitter
B. The minimum amount of power needed to complete the contact
C. No more than half the rating of your linear amplifier
D. Never more than 1 watt

Only the power needed for the contact should be used, especially for satellite communications, answer B.

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

T8B04 [97.301, 97.207(c)]
Which amateur stations may make contact with an amateur station on the International Space Station using 2 meter and 70 cm band amateur radio frequencies?
A. Only members of amateur radio clubs at NASA facilities
B. Any amateur holding a Technician or higher class license
C. Only the astronaut's family members who are hams
D. You cannot talk to the ISS on amateur radio frequencies

The rules say any Amateur can contact a space station, subject to being permitted to transmit on the uplink frequency; and the bands shown are authorised for Technicians, and above (but not Novices), answer B. 97.207(c) specifies the bands and sub-bands permitted for space operations; while 97.301 states Technicians may use those listed.

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 information about a satellite

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 light, although some military birds use lasers to communicate. What antenna the beacon uses varies, but it is a transmission, NOT an antenna.

Which of the following are inputs to a satellite tracking program?
A. The weight of the satellite
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 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 when referring to 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 in line with the signal receives poorly, so as the satellite, and its antennas rotate, the signal will fade in and out, or at least weaken considerable, answer B.

What do the initials LEO tell you about an amateur satellite?
A. The satellite battery is in Low Energy Operation mode
B. The satellite is performing a Lunar Ejection Orbit maneuver
C. The satellite is in a Low Earth Orbit
D. The satellite uses Light Emitting Optics

Most (currently all, I believe) Amateur birds are in Low Earth Orbit, answer C. Many are in a polar, or near polar orbit.

What is a commonly used method of sending signals to and from a digital satellite?
B. PSK31
C. FM Packet

FM packet, as mentioned regarding the "store-and-forward" birds, is used for sending data through digital satellites, answer C. FM based modes better handle the Doppler shift. PSK31 and WSJT are terrestrial low speed, weak signal data modes, and upper side-band audio frequency shift keying is something like radio-teletype.

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, December 2017.

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