Contents

Australian Amateur Radio FAQ

Last updated: 24-Jun-06

Special Interests in Amateur Radio

VHF/UHF DX/weak signal operation

While interstate contacts are routinely made on the HF bands, many people enjoy making long-distance contacts on VHF/UHF SSB. Even with fairly low power, the use of SSB allows longer distance contacts than is the norm with FM and repeater operation. The amateur six metre (50 MHz) band sometimes provides intercontinental communication, while enhanced conditions on the higher bands (particularly during the summer) allows distances of thousands of kilometres to be covered.

VHF/UHF operators often specialise in particular propagation modes. Some wait for meteor showers and use meteors to reflect signals back to earth. Others bounce their signals off aircraft, particularly those serving the busy Sydney - Melbourne route. Really serious operators build massive antennas and bounce signals off the moon to communicate worldwide. Because signals are weak, morse code is more popular than SSB for this mode. Closer to earth, some amateur satellites are equipped with linear transponders which allow intercontinental VHF/UHF SSB communication.

An advantage of VHF/UHF is the large amount of gain obtainable from relatively small antennas. Operation from hill-tops, with portable equipment is another attraction of VHF/UHF SSB operation. The WIA holds several contests in the spring-summer months to encourage this type of operating. More information about VHF SSB operation can be obtained from the website of the VK2 VHF DX Group and from the VK-VHF mailing list.

Propagation of VHF signals Again, VHF/UHF signals differ from HF signals in the way they achieve long distances. Whereas HF signals generally are reflected by the higher layers of the ionosphere, enabling reflected signals to travel long distances around the earth, those layers usually do not reflect the VHF, UHF and higher frequencies. This is due basically to smaller wavelengths requiring denser levels of ionisation than longer wavelengths to be reflected efficiently. A theoretical/nominal cutover point of 30 MHz, neatly representing the wavelength of 10 metres, is normally regarded as the cutover between HF and VHF, the idea being that HF signals get reflected by the ionosphere (layer F) and VHF signals occasionally get reflected by the E layer but usually are not reflected at all. In practice nature is not so cooperative with this theory and the cutover point varies hour by hour, day by day and year by year. There is at any time a changeover frequency, usually between 10 and 100 MHz, depending on the point in the sunspot cycle and the current actual sunspot activity, at which ionospheric reflection via the upper layers (usually F layer) ceases to operate and signals at frequencies higher than that level are not reflected, while frequencies lower than that level continue to be reflected. This is probably not a precise definition of the maximum usable frequency (MUF) but this illustrates the concept well enough. The E layer of the ionosphere also occasionally contains clouds of ionised particles that do reflect radio signals and this effect can be observed at frequencies of between 25 and 60 MHz every year, with occasional extensions above 100 MHz. In the Australian summer of 2006/7, sporadic E layer ionisation on several days of November and December 2006 supported many radio contacts on the 144 MHz band, with distances of well over the usual workable distances. Contacts were made between southern, northern and western Australia over distance of over 2000 km. The E layer also is involved in a propagation mode called Trans-Equatorial Propagation (TEP). Articles on this kind of propagation are:

So what distances can I reach using ordinary VHF or UHF propagation

The VHF bands are often regarded as "line of sight" bands with little opportunity to make contacts over the horizon. In fact contacts are readily made well over the line of sight distance on bands up to 1296. As the frequency gets higher, atmospheric losses increase. But on 144 MHz distances of 500 km are common, with well equipped stations at both ends, using high gain antennas. Typical station equipment would be:

144 MHz SSB transceiver with 100 watts output
10 to 15 element yagi beam antenna, at a height of 6 to 12 metres above ground level and with reasonably unobstructed "view" in the desired direction, fed by low loss coaxial cable
Some stations would also use a mast-head amplifier to improve receiver sensitivity

The more serious operators would use 400 watt transmitters and either a single long yagi of up to 14 or 16 elements (on a boom of up to 6 to 8 metres length) or an array of 10 or 12 element yagis (each having boom length of about 4 metres).

An array of four high gain antennas combined with a good quality receiver preamplifier would enable a 400 watt station to use moonbounce techniques to make overseas contacts.

On 432 MHz similar transmitter power levels are used, but antennas can be of much higher gain because the wavelength is correspondingly smaller. Cable quality has to be increased to avoid loss of signal on both transmit and receive. Cable that is quite acceptable on HF bands tends to act like a big lossy dummy load on even 432 MHz, with not much power reaching the antenna, or getting from the antenna to the receiver.

Microwaves

Microwave frequencies are useful for more than cooking food. Most people are aware that space missions communicate using the microwave frequencies and we have seen the pictures of huge dishes used by space tracking stations such as those at Tidbinbilla, ACT for communicating with satellites and manned space missions.

Radio amateurs also successfully use these frequencies for interstate and earth-moon-earth amateur radio communications. The gigahertz amateur bands hold a special appeal to many experimentally-minded amateurs, and there is still much scope for experimentation. While commercially-available equipment for these bands is not common, a range of easily-built kits has recently come available that allow operation on these bands. Once again, the use of very high dish gain antennas means that only a small amount of power is needed to establish communication. Like with the VHF/UHF bands, tropospheric ducting can allow thousands of kilometres to be spanned over large expanses water, such as the Great Australian Bight.

Australian microwave enthusiasts have their own mailing list to set times for tests and discuss equipment and antennas. There are several good websites dealing with amateur microwaves, including that maintained by Robbie VK3EK.

FM and Repeaters

One of the most popular modes enjoyed by amateur operators, FM and repeater operation takes place on the 29, 53, 146, 432 and 1296 megahertz amateur bands, with two metres (146 megahertz) being the most used. The FM mode enables good speech clarity, and the use of repeater stations (usually erected on hilltops) permits effective local-area communication, even from low-powered, handheld or mobile stations. While a single repeater normally permits communication over a 50 to 150 kilometre radius, the linking of repeaters can allow distances of several times this to be spanned. Where a good direct path exists between stations, simplex (direct) communication becomes possible, without the need for a repeater.

Most repeaters only use a pair of frequencies in a single band. However in some areas several repeaters have been linked to allow extended range communication. Other repeaters may have inputs and outputs on more than one band. An example is one that links allows stations on VHF/UHF to transmit and receive on 29 MHz FM. The idea is that long-distance contacts become possible via just a VHF or UHF handheld transceiver if conditions on 29 MHz are favourable.

Repeaters are built and maintained by volunteers, and are paid for by local radio clubs, repeater groups, and/or WIA Divisions. It would be courteous to join one or more of these bodies if you intend using the repeater much.

A full list of Amateur & UHF CB repeaters in Australia, in order of band within state, is maintained by Allan VK2CA and can be found at http://www.vkham.com/ A mailing list is also available for those interested in repeaters.

Internet Repeater Linking

A rapidly growing amateur radio activity is the linking of amateur repeaters via the internet. The technique has been used since the early 1990s. The first popular system was called I-Phone, which was based on a Windows operating system. I-Phone's popularity peaked on January 26, 2001, when amateurs throughout Australia and internationally communicated via a special Australia Day link-up of repeaters.

A newer system (known as Internet Repeater Linking Project or IRLP) has since supplanted I-Phone. IRLP, developed by David Cameron VE7LTD, is based on the Linux operating system. It is more reliable than I-Phone and is easier to use. Further information on IRLP appears at http://www.irlp.net

Satellites

One of the most exciting fields in amateur radio is the amateur satellite program. There are several small satellites orbiting the earth. These have been built by radio amateurs and are used by amateurs from around the world. AMSAT is the world-wide body which coordinates satellite construction, and lobbies for spare space on commercial launch vehicles. These satellites permit communications by morse code, voice, or packet radio, over large distances using line-of-sight frequencies in the VHF and UHF spectrum.

Low orbit satellites are the easiest to use. They can be used with low power and modest antennas. Examples of low orbit satellited include the Russian RS series and South Africa's Sunsat (SO-35) satellite. The sensitivity of this satellite was so good that amateurs operating from buses, trains and trams have been able to make contacts though it! Low earth orbit satellites have short pass-times (15 minutes typical) and are good for communication up to a few thousand kilometres. In contrast, other satellites require more power and bigger antennas, but allow global contacts to be made.

For information on current amateur satellites and satellite communication, please see http://www.sckans.edu/~sireland/radio/amsat.html and http://www.qsl.net/vk3jed/. There are many websites giving information about satellite operation. Find them using any search engine.

SAREX

SAREX stands for Shuttle Amateur Radio EXperiment. This is the Shuttle Amateur Radio Experiment program operated by AMSAT in cooperation with NASA. From time to time space shuttle crew who are also licensed amateurs are allowed to take radio equipment into space. Hundreds of contacts with amateur stations on the ground ensue. Noteworthy has been the involvement of schools in many SAREX experiments.

Television

Yes, an amateur radio licence (other than Foundation level) is also your amateur television licence, if you're so inclined.

The signals transmitted are just like those from the conventional ABC, SBS and commercial TV broadcasters, though at somewhat lower power. Transmissions are usually in colour, and have the usual sound accompaniment. Some cities have amateur television repeater stations, which retransmit signals from amateur television operators. In some cities these transmit on UHF Channel 35, so can be received on a standard UHF TV set. Sydney is perhaps the most active, with ATV transmissions from the Gladesville Amateur Radio Club on Wednesdays, Fridays, and Saturdays. In Melbourne, activity is centred around the VK3RTV amateur television repeater. Though this operates in the 420 - 450 MHz band, it can still be watched on many standard UHF TV sets, provided that they tune down to about channel 16 (extreme bottom end of band, below SBS Ch 28). Because ATV is weaker than signals from the usual broadcasters, a correctly positioned outdoor antenna and (possibly) a masthead preamplifier are required to achieve best reception in most areas.

Packet Radio

Anybody at all familiar with digital communications, will know of packets. Data are sent in discrete bundles, called packets, which can be individually checked for integrity and acknowledged (or NAK'ed), and processed, or routed on to somewhere else. Packet radio is exactly the same thing, except that the packets fly through the air with the greatest of ease, instead of being sent over wires.

Many people who have an interest both in computers and radio, find packet radio experimentation to be a natural marriage of the two fields. The basic protocol used in packet radio is called AX-25, an adaptation (some would say, bastardisation) of X.25. Error correction is achieved through a 16 bit cyclic redundancy check (CRC). Although AX-25 is by far the most common protocol in use, amateurs are free to experiment with other protocols which meet the ACA identification requirements. This is unlike some countries, which are forced to use AX-25.

Most VHF packet activity happens at the lightning fast speed [:-)] of 1200bps (bits per second) (though there is some use of a 4800 bps standard in areas such as Canberra and there is an increasing number of radios rated for 9600). To make matters worse, it's half duplex (because off-the-shelf radios themselves are half duplex devices). So if you're used to 56 kb/s from your internet modem, you're in for a bit of a shock with packet! And if that's not slow enough already, many people can (and usually do) use a single packet frequency at once, so the available bandwidth is divided between all the users.

The news isn't all bad, however. Some TNCs have built-in 2400bps modems, and there are readily available modem designs that operate at 4800, 9600, and 56K bps, and if you can find somebody using one of these faster modems, you don't have to talk at 1200. There's even amateurs in the US experimenting with 2Mbps full duplex over microwaves -- that's as fast as ISDN primary rate!

Packet bulletin board systems (BBSs)

Packet radio, being a digital communications mode, lends itself to unattended operations, such as BBSs. Packet BBSes are similar in many ways to the old dial-up bulletin boards, with file areas, messages, bulletins, automatic forwarding to other boards, and so on. Messages and files tend to be related to amateur radio. As with all forms of amateur communication, the amateur regulations restrict the content of material transmitted through packet BBSs. Packet radio is largely free of the vulgarity that characterises some internet newsgroups, though 'flame wars' can still break out.

The packet BBS network spans a large part of the globe, and is linked by VHF over short distances. Amateur satellites, HF radio and internet links carries traffic between countries. If you wish to sample the packet BBS network, look at the contents of the VK5BBS system at http://nerc.vk5bbs.ampr.org/

Bandwidth limitations mean that you won't find large files on packet radio. Because of the mode's slowness (for most users), large messages (especially to international sites) are frowned upon. Packet Radio can be considered the 'poor man's internet' as use of the system is free to anyone with an amateur radio licence and suitable equipment.

How do I get into Packet?

Because packet radio uses isochronous communications (essentially start/stop synchronous), you can't just connect an internet modem up to the regular serial port in most PCs, and use it for packet.

Most packet operators use a device called a TNC (terminal node controller) which is about the size and shape of a telephone modem, and connects between a standard asynchronous serial port, and a radio transceiver. However, it's much more than a modem, it operates as a PAD (packet assembler-disassembler), and also provides a user interface to facilitate the setting up and tearing down of connections to other packet systems.

The advantage of the TNC approach is that it works with just about any computer (personal or otherwise) with a standard asynchronous serial port. Also, because it is dedicated to packet, and does all its framing and such in hardware, it can operate at relatively high speeds.

A cheaper alternative is to do all that in software, and bit-bang the packets by toggling a bit of an I/O port on and off. The only extra hardware you need for this is a simple FSK modem, which can be implemented with a single 16 pin chip, a crystal, and little else. Software to work with such modems is available for a variety of computer platforms, including the IBM PC range.

For further information on packet radio in Australia, please see the Australian Amateur Packet Radio Association's website. They have a software library online at http://members.optusnet.com.au/aapra/shareware.html too.

Can I use Packet to access the Internet?

No. There are some (indeed, many) connections between the amateur packet network and the Internet, but these are very carefully set up in order to prevent any breaches of licensing conditions. Specifically, most of these connections take the form of wormholes, which allow the Internet to serve as a backbone for amateur traffic over paths which can't be adequately served by radio.

The only traffic which passes out of the Internet and into the packet network through these wormholes is traffic which originated in other amateur packet networks, so no laws are broken. Nobody to our knowledge gateways news to packet, because each message has to be checked for suitability, and the packet networks currently in existence don't have the necessary bandwidth in any case.

Automatic Position Reporting System (APRS)

A fast-growing interest in amateur radio is automatic position reporting system or APRS. This is a system that combines the global positioning system (GPS) with packet radio to allow transmission of location data. Receiving stations can get real-time information on the location of a APRS-equipped station. Amateurs have already used APRS technology to assist in providing communication for sporting events. APRS also has many commercial and emergency applications. Here is some information on APRS in Australia.