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Amateur operators from Technician and up are permitted to operate via amateur radio satellites. In legislative documents, including ITU ones, this is referred to as the Amateur Satellite Service, somewhat distinct from the Amateur Service. Specific amateur bands or sub-bands are authorised for this service, these being globally available amateur frequencies. There is not a specific text that Novices shall not operate via satellites, but rather their permitted frequencies do not align with authorised satellite uplink frequencies.
As of writing, all Amateur Satellites, are "Low Earth Orbiting", or LEO satellites, meaning that the they move fairly rapidly across the sky. A polar orbit, which is common, means that the satellites move in a north to south, or south to north direction, depending on the time of day. The time an orbit takes is the "period", and this typically increases with height. For a LEO at a few hundred km up, the typical period is around 60 to 90 minutes. As the satellite orbits, the earth turns below it, meaning one orbit might pass over New Zealand, another over eastern Australia, then next over SA & NT or Western Australia, the Indian Ocean, and so on. A pass is called an ascending pass pass from south to north, while a descending pass is from north to south.
Put a "bird" at around 36,000 km above the equator, and its period is just under 24 hours*, meaning that its period matches that of the earth's rotation, kind of handy when we want to bang a pipe into the ground, and mount a simple dish to watch TV. We call this geostationary or geosynchronous. Phase 3D was an AMSAT project to do this, and there is some possibility that a satellite may one day contain some sort of Amateur capability. Certainly, similar capabilities exist to support soldiers with portable VHF or UHF radios, over a wide theatre.
* Just under 24 hours? Yes, the earth takes about 23 hours, 56 minutes, and 4 seconds to rotate, but in this time we have completed just under 1 degree, or about one 365th of orbit around the sun, so it has to rotate for 3 minutes 56 seconds (~1/365 of a turn) for the same point to face the sun as 24 hours before.
LEO orbits have the advantage of little delay between transmission and reception of a signal. The disadvantage is that the motion of the satellite relative to the user causes a Doppler shift in the frequency the ground station observes, typically by some kiloHertz. Doppler effect is most commonly observed by a pedestrian as car, emergency vehicle, train, or aircraft passes. Perhaps a rail passenger notices it while passing a level crossing, the ding-ding-ding becoming dong-dong-dong.
A typical orbit speed of a LEO satellite is around 7-8 km per second, or 25,000 km/h. The variation of apparent speed as the satellite transitions from approaching, to overhead or abeam, to receding, causes the frequency shift to change from high to zero to low.
For commercial digital telephone systems such as Iridium, the digital voice system means the Doppler shift is not heard in the audio.
A range of upper HF, VHF, UHF, and SHF frequencies are authorised for satellite operations. A short-hand regarding the uplink and downlink frequencies used is called "modes", with letters standing for the bands. You would however need to consult tracking software or more likely a website regarding the satellite to know the exact frequencies. Periodically, the operators of the satellite may change the mode (bands) used, and publish a statement that the bird is now in, say U/V mode, or there may be a schedule of modes.
|H||15 m||21 MHz|
|A||10 m||29 MHz|
|V||2 m||145 MHz|
|U||70 cm||435 MHz|
|L||23 cm||1.2 GHz|
|S||13 cm||2.4 GHz|
|S2||9 cm||3.4 GHz|
|C||5 cm||5 GHz|
|X||3 cm||10 GHz|
|K||1.2 cm||24 GHz|
|R||6 mm||47 GHz|
Cross-banding is used partly, because this removes the need for the large, heavy, and mechanically fragile cavity filters used on earth-bound repeaters.
A range of antennas can be used, depending on the band.
For HF, VHF, and UHF, simple antennas are used. For HF, a wire antenna will be sufficient. For 2m and 70 cm, whips can work, although these perform poorly while the "bird" is overhead. A "turnstile" is more complex antenna which works while the satellite is in any location. If more gain is needed, yagi, and similar antennas are used.
One popular design is the "Arrow" unit for 2 metres and 70 cm, with elements made from aluminium arrow shafts. These have a linearly polarised VHF yagi in one plane, and a UHF one in the other. As they are often used hand-held, the polarisation and pointing can be adjusted as needed.
The gold standard is however to use circularly polarised antennas. These typically consist of a boom with elements rotating 90 degrees every quarter wavelength along the boom. A spiral is also an option. While single-boom options exist, often a cross-bar is used, with VHF and UHF antennas mounted, such that they track together. The cross-bar is mounted on an "El-Az" rotator, allowing the antennas to be pointed at any part of the sky, and to track the "bird" under control of software. An example of an Elevation and Azimuth unit is the Yeasu G-5500. This is a nice match with the FT-847.
A QST article on Circularly Polarized Yagi Antennas.
These are used due to Faraday rotation in the signal.
For upper UHF, and beyond, often a dish is used.
AMSAT is an international association which builds Amateur satellites. Their website is: amsat.org
To avoid confusion the term "mode" is avoided in the exam, but a range of what are normally called modes are used, depending on the satellite. Some have a linear translator, which can handle FM, CW, SSB, PSK and Packet (FSK), among other modulation systems. Some satellite operating groups suggest FM is only used at certain times, as it has wide bandwidth. It is important to only use low power to transmit to a satellite with a linear transponder, as high power makes it wind back its gain, and thus reduce the power level of other uses who are using the correct power level.
Not mentioned, there are also simple FM cross-band repeaters, and one has been operated aboard the ISS.
One form of Amateur satellite is the store-and-forward packet radio one. At least one was tested as an amateur device, then converted to humanitarian use on non-ham bands, perhaps uploading messages from a hospital in a remote African location, and downloading them while over the organisation's HQ elsewhere, and vis-a-versa; before reverting to Amateur use. Africa now has extensive mobile (cellular) 'phone coverage.
From 70 centimetres and up, fast-scan television is permitted.
"Never Twice the Same Colour"? Or officially, National Television Standards Committee, this was the commercial first colour system developed, and is only being discontinued in smaller stations now. Later, European standards do not require a tint or hue control to balance the colours.
Outside things like Amateur TV this has been replaced by digital systems, like DVB-T, DVB-S, and ASTC. Surplus DVB-S, meaning satellite, encoders have been used for terrestrial DATV - Digital Amateur TV, and DVB-T encoders are also becoming available, probably as broadcast stations move from MPEG 2 to MPEG 4 encoding. One Victorian stationis using DVB-T2.
Related to the 60 Hz mains, American B&W TV used 30 frames per second, and 60 interlaced fields, as in one field, the odd lines are scanned, then the even lines in the next. NTSC uses 29.97 frames, which is still compatible with B&W TV.
The colour content is called the "chroma", from chromatic, a term related to colour.
As CRT (cathode ray tube) used electromagnetic scanning windings on a large vacuum tube to scan a beam of electrons across the phosphor, there is a period which it must be "blanked", or turned off, during the "flyback" period, and likewise, from the bottom to the top of the screen.
NTSC, and the related B&W system both use VSB, vestigial sideband band. VSB allows a narrower signal than AM, while using simpler detector equipment than pure SSB would require. The bandwidth is around 6 MHz. An alternative analogue system is FM. This has around 12 MHz bandwidth, so only 23 cm and up has enough room. 1255 MHz is a frequency used for this. This is compatible with old analogue satellite receivers, although pre-amplification is often needed.
Off the exam, as you may expect, PAL, having been the colour system used in Australia, UK, Germany, etc, is used in ATV in these countries. SÉCAM has been used in France and related countries, although there has been a move to PAL by hams, with both systems sharing scan and frame rates.
A related system is slow-scan TV. Originally it used some form of frame capture from a video camera, but the modern system sends images from a PC. Brightness is indicated by the tone (audio frequency). There are typically 128 or 256 lines in an image, and a new line is indicated by specific tones. Bandwidth is limited to 3 kHz. Even where a PC is used, this is still an emulation of an analogue SSTV signal.
Special tones indicate things like the start of a line, and help identify the system in use. Within each line 1500 Hz might represent black, 2300 Hz white, and tones between levels of grey.
One question asks about DRM (Digital Radio Mondiale), normally a digital audio broadcasting mode, but with the ability to send images, such as logos and album cover-art. The encoding method has been borrowed to send SSTV images. As this is done in voice width channels, bandwidth is limited to 3 kHz. Coding an decoding can be done on a PC with a soundcard.
The reference to a "special IF converter" in the distractor relates to using a PC to listen to high bandwidth or multi-channel broadcast DRM, where a radio needs an IF tap, or at least a dummy IF filter consisting of a capacitor and a few jumpers, to handle a 12 kHz wide signal.
These are the actual questions from the Extra licence exam pool, as published by the NCVEC.E2A01
This is a south to north pass, answer C.
If you watch a pass on software, or a preview, you will notice it moving up the screen. Likewise, if it is shiny, and illuminated by the sun, you may visually be able to see it moving northwards.E2A02
All these occur, answer D.E2A03
This done via the mixer taking the difference rather than the sum, answer D.E2A04
This is the frequencies or frequency ranges used for uplink and downlink, each band being assigned a letter, answer B.E2A05
These are the uplink and downlink sub-bands, answer D.E2A06
"Keps" define the orbit of a satellite, allowing its location to be predicted, answer A.E2A07
All these modes, and more are possible, answer D.E2A08
Because these receive a band of frequencies, say on 70 cm, and retransmit this in a sections, of say, 2 metres, and because they handle modes such as SSB which require linear conversion, they use an automatic level control to control the gain during the frequency conversion and transmission process. If you operate at a high power, or with high gain antennas, you will wind back this gain, and thus reduce the downlink power of the other users, answer B.E2A09
These refer to the 23 centimetre and 13 centimetre bands, answer A.E2A10
These are "Geostationary" birds, answer B.
This means they appear stationary with respect of the earth (Geo). These are typically used for TV broadcasting, some audio broadcasting, Internet for remote areas, and some military communications.E2A11
A circularly polarised antenna receives the signal well, no matter the polarisation, so can work well with a signal which is varying in polarisation due to physical rotation or Faraday rotation of the signal, answer B.E2A12
If an Australian ham writes a packet message to a Spanish station, it is upload from a gateway in VK, then download to a gateway in Spain for distribution to the Spanish station, answer C.E2A13
Store and forward satellites transfer messages by physically travelling between the area above different users and gateways to areas above other gateways, as they orbit, answer B.E2B01
American B&W TV used 30 frames per second, and NTSC uses a very similar figure, answer A.
As the images are interlaced, there are two fields per frame, and these occur at twice the frame-rate.E2B02
There are 525 lines in US analogue TV, answer C.
Not all are visible, hence the smaller number of lines used in both VGA screens, and ATSC video.E2B03
For each frame, there are two fields, one of the odd lines, the next of the even lines, answer D.
Digital video resolutions with an "i" on the end are interlaced; with a "p", progressive scan.E2B04
Firstly, note that this is analogue slow-scan, not normal TV. Thus the answer is that the colour information is sent by sending the red, green, and blue lines sequentially, answer A.
There are a few variations on this theme.E2B05
VSB needs far less bandwidth than full AM, but unlike pure SSB, preserves phase information in the low frequency components, allowing for simple video detector circuitry, answer C.E2B06
This for fast-scan analogue TV, this is a modified form of AM, in which one complete sideband, and a portion of the other are transmitted, answer A.E2B07
This is the "Chroma", answer B.E2B08
Some TV sets are designed to work with a system where unencrypted analogue TV channels are fed into a cable, and can apparently be received without a set top box. By transmitting on these channels, a standard TV, perhaps with a masthead amplifier, can watch these signals, answer A.E2B09
Given it is within the normal SSB passband, nothing other than a PC with a "soundcard" or normal audio functions is needed, answer D.E2B10
This is the tone frequency, answer A.E2B11
These allow the software to identify the kind of SSTV signal being sent, answer B.E2B12
Specific tones indicate the beginning of each line, answer A.
On to: Operations 2 - Contesting, QSLing, VHF+ Digital, & EME
You can find links to lots more on the Learning Material page.
Written by Julian Sortland, VK2YJS & AG6LE, May 2022.
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