Short Wave Communications

Resilient communications between a group of individuals can fairly easily be achieved over modest distances using relatively inexpensive equipment as discussed in the communications page, many of the solutions not requiring specialised licensing. If it's important to establish links over longer distances, say tens or hundreds of miles, then the options become much more limited.

One of the simplest options is to invest in satellite telephones and/or satellite internet. Whilst these both depend on infrastructure outside of the control of the individual they can probably be expected to remain in service under most emergency situations. These are commercial services and terms and conditions vary over time. Satellite systems are popular with journalists in war and disaster zones, also with explorers and long distance sailors who need fall-back communications in case of a need to be rescued. Cost is likely to be an issue with any of these choices and if you wish to pursue it, you will find a number of services with varying availability and cost.

A fully independent option is to use radio which can cover longer distances than the few kilometres/miles already discussed. This is a specialised area, requiring the use of specific licences and will not be of interest to most groups. It is, however, a topic that should be understood and is fairly widely discussed by survivalist or 'prepper' groups and so this page will explore the basics in enough detail to allow you to make an informed judgement. There is a basic level of technical information that's essential to understand the topic but it will be kept to a minimum.

How Does Radio Work?

Radio uses what are usually called radio waves, but in reality are an example of electromagnetic radiation^[1] (EM for short), a fundamental feature of how the universe works - the most obvious example being visible light which is exactly the same phenomenon as radio waves.

EM radiation is a vibration of the electrical and magnetic properties of space. How rapidly the vibrations occur is measured in Hertz (Hz), 1Hz being one vibration a second, i.e. the frequency of the wave. Radio waves of interest to us are typically in the millions to billions of Hz (1 million is 1MHz, 1 billion 1GHz). Visible light vibrates at some millions of billions of Hz. Cellphones typically use around 1-2GHz and a lot of short-range devices use Wifi or Bluetooth at 2.4GHz. Satellite TV uses around 10GHz.

The higher the frequency, the more the waves behave like light itself, travelling only in straight lines and easily blocked by opaque objects, especially ridges, hills and of course, the Earth itself at the horizon. The most popular hand held radios typically use around 400 MHz so whilst they can get through limited amounts of shrubbery or pass through thin walls, there's a limit to how much of that they can overcome. From a hand held radio at 1.5m height, the theoretical distance to the horizon is 4.4 kilometres / 3 miles or so, putting an upper practical limit on range unless you or your correspondent can find a hill to stand on.

Light travels at a fixed speed, very close to 300,000 km/s (186,000 miles per second), so a 1MHz radio wave travels about 300 metres in a single vibration. This is of importance to radio engineers who will often switch between speaking of frequency in Hz or wavelength in metres. The two terms are considered interchangeable since there's a fixed ratio between them.

In the early days of radio's exploitation it was discovered that low-frequency (i.e. long wavelength) signals tended to hug the ground and travel far over the visible horizon. To begin with, broadcasting used wavelengths in the kilometre range, say 0.2MHz, and higher frequencies were discounted as useless since they didn't travel well over the horizon. Quite soon though, it was discovered that higher frequencies with shorter wavelengths could bounce off layers high up in the atmosphere (the ionosphere) and be reflected back to ground far over the horizon.

As soon as the long-range properties of higher frequencies were discovered they were rapidly adopted, with the generic term 'short wave' being used to differentiate them from the initial belief that longer wavelengths were better.

The part of the radio wave that hugs the ground is called the ground wave, if part gets reflected back to ground it is called the sky wave. The ionosphere that reflects the wave is caused by the intensity of sunlight acting on the atmosphere so the properties of the ionosphere vary substantially between day and night - reliable radio links will typically use different frequencies at different times of day. The upper layers of the ionosphere continue to reflect even after dark but the lower layers disappear with the sun.

As you move up in frequency, the ground wave range decreases and (to a point) the sky wave range increases, leading to something called skip where no signal can be received - the ground wave having died out and the sky wave not coming down yet, so there is a dead zone where there is no reception even though beyond the skip zone strong signals may be arriving. Also, during the day time, the part of the ionosphere closest to the ground is heavily absorbent of lower frequencies, eliminating the sky wave during daylight hours at the low frequency end of short waves, with the effect disappearing at dusk.

Practical short wave frequencies are from approximately 2-30MHz. From about 20MHz waves tend to go straight through the ionosphere rather than being reflected back, although under certain solar conditions they can be spectacularly effective. At the higher frequencies it's not uncommon to hear signals with a pronounced echo as you hear them on their first, second and maybe third time around the whole planet (round trip time is about one-seventh of a second).

The sun has an eleven year cycle of sunspot activity. During the high activity part of the cycle the higher short wave frequencies become much more useful whilst at the low part of the cycle they may be of little to no use at all. This is very noticeable with CB radio which uses 27MHz and may suddenly 'open' to extreme range possibilities during solar peak activity, even though most of the time it's hard to achieve more than a few miles reliably. The amateur 28MHz band has identical properties to CB and permits more power to be used - under good conditions it would not be surprising to speak direct to the USA from a car whilst driving.

Licensing

Because of the distance short waves can travel, every country requires short wave broadcasters to have a licence. It's common for shipping to have a licensed radio operator using short waves from distant oceans. Aircraft also use short wave communications during transcontinental journeys, Shanwick air traffic control for Europe-USA for example operating at a range of frequencies such as 3.016MHz, 5.598MHz, 8.906MHz and 13.306MHz, see Shanwick Radio^[2].

Unless you are an ocean-going leisure sailor, there's no simple route for a non-commercial user to obtain a licence to use short waves. However, there are a number of frequency allocations for amateur/leisure use and a basic amateur radio licence is not particularly hard to obtain. In the UK there are three types of licence varying in technical content and difficulty. A basic 'foundation' licence is not highly challenging, taking maybe 10 hours of study with an examination at the end. Whilst a foundation licence is somewhat restricted, it allows its owner to start using modestly-powered short wave radio as long as commercial and type-approved equipment is used (which includes approved home-construction kits). Higher licences permit higher power levels and also to home-design and construct equipment.

The official body regulating radio licensing in the UK is OFCOM, which has a section on their website providing information about amateur radio ^[3]. OFCOM delegates the practical business of training and examination for amateur licences to the Radio Society of Great Britain. The RSGB website contains further information on amateur licensing in general ^[4] and also useful information on courses and tests ^[5]. Training can be found in amateur radio clubs and also online, with online testing also available. The RSGB has a specific section on the foundation licence ^[6] which is a good starting point if you are interested.

Practical Amateur Short Wave Radio

By international agreement there are certain frequency ranges allocated for amateur use (sometimes shared with commercial users). These are typically referred to as 'bands' and often by wavelength rather than frequency. e.g the 160m, 80m and 40m bands (approx 1.9Mhz, 3.6MHz and 7MHz). There are allocations at lower frequencies and also numerous higher frequency bands, but the three mentioned are particularly interesting for country-wide coverage. To an extremely rough approximation their useful properties are listed below, on the assumption that you are using fairly modest power commercial equipment and based in the UK.

British licences like most other countries only permit amateurs to speak to other amateurs or to cooperate with emergency services on their request. Profanity, advertising, commercial use or playing music is prohibited. Every licence comes with a distinct call sign which must be used by the licence holder for identification on air at specified intervals. Groups of amateurs sometimes refer to each other by a few letters from their respective call signs rather than first names as there may be multiple 'Jacks' or 'Jills', but there will be only one known to them all as 'ZBV': this curious habit may be baffling to outsiders. Encrypted communications is not generally permitted so there is no actual privacy.

There are many ways of transmitting information by radio, known as modes. The simplest is just turning on and off the transmitter to send the dots and dashes of Morse Code, but most people will probably want to use voice communications using single sideband (SSB). SSB takes the audio frequencies present in voice and transposes them up to the radio frequency either unchanged Upper Sideband (USB) or, for historic reasons, inverted Lower Sideband (LSB). Digital modes also exist but are generally used only by hardcore experimenters. There's also a vintage mode Amplitude Modulation (AM) dating back to the early 20th century which some enthusiasts use to keep it alive. The mode known as FM (frequency modulation) is never used in practice on short wave bands although in theory it could be.

It may be surprising to find that Morse Code is still used but it remains one of the most effective modes for getting messages through using low power in adverse conditions. That, combined with the remarkable ease of building a Morse transmitter, continues to keep it popular with those who have the niche skill of using it. Kits to build low power Morse-only radios are available at much more affordable prices than voice transceivers. The area of very low power Morse-only communications is generically known as QRP from the Morse abbreviation for Reduced Power. Skilled operators use an extensive array of standard abbreviations (like 'text speak') and communication speeds of around 50 words per minute are not unusual.

An effective antenna is essential for short wave radio, typically a length of copper-coated steel wire (for strength), or just copper. Steel wire by itself doesn't really work. The antenna should be as high as possible above the ground and needs, ideally, to be half a wavelength long as shorter antennas work much less well. The antenna must be connected to the radio through an antenna tuning unit (ATU) which will need adjusting on any significant frequency change. The radio is known as a transceiver, meaning transmitter-receiver. Power levels will usually be in the range of 5-200 watts, depending on the band and the licence conditions. The maximum power allowed in the UK is 400 watts but such high powers bring risks, with the antenna needing to be protected for safety reasons. High radio power doesn't electrocute but it can produce nasty burns.

Handheld radios are impractical for short wave transmission, though reception can work well if the receiver is designed for the mode of transmission being used, which for voice will almost always be SSB.

In general, higher power translates into further range, unlike the frequencies above 100MHz or so where more than a few watts makes little difference. Often, as little as 5 watts will be all that's needed but if you have atmospheric noise to overcome or other unfavourable conditions, having 50 watts or more available makes a real difference.

Broadly speaking, communication can never be 100% guaranteed as the state of the atmosphere is critical. Messages may have to be postponed during bad conditions and delivered when things improve. The ability to pick which band is working well may be necessary, as one may be unusable while another is problem-free.

Amateur radios are often installed in vehicles and used both stationary and moving. These are often known as mobiles, as distinct from hand held radio usage which is less often referred to as portable.

Finally, if you talk to other experienced amateur operators, you will find a certain amount of jargon in use. Some of this derives back to Morse Code abbreviations (QRM - static/noise, QSB - fading of the signal, QTH - my/your location, QRX - please wait/standby, 'rig' for equipment, WX for weather conditions) and numerous others which may take a short while to learn. This is not uncommon in any trade or profession of course.

160m Band

The useful range is typically 20 or more miles during daytime by ground wave, with no useful sky wave until after dark at which time some hundreds of miles are probable. After dark, for example, the west of Ireland and much of Europe come into potential range from the middle of England. Lots of atmospheric noise may be a problem and thunderstorms a hundred miles away can be a severe nuisance in the summer as can rain-borne static electricity, fortunately any or all of these are occasional rather than frequent. Antenna size may be a limiting factor as 80m of garden is a lot although people do manage well with shorter antennas. Local electrical noise from TVs and computers can render some locations barely usable. 160m is not much affected by skip. In the UK, prior to 145MHz equipment becoming widely available and affordable this used to be the preferred band for local contacts including from vehicles despite the ludicrous wavelength/antenna mismatch inherent in a car-mounted installation.

Despite the apparent drawbacks mentioned above this is an entirely practical band for short to medium distance communication in the UK. It has somewhat fallen out of favour since the widespread cheap availability of equipment for the 2m and 70cm bands coupled with general access to repeaters has pretty much replaced what it offers, apart from the after-dark long range capability. In a grid-down situation repeaters will probably not work and then having 160m available would be very useful.

80m Band

This is typically useful for intra-UK communications during daylight with a mix of ground and sky wave since daytime skywave is somewhat less attenuated than 160m and the band is generally less affected by local noise than 160m though not immune. Reliable distances increase greatly after dark with the downside that loud continental stations may drown out more modestly powered local communications. Some skip effects may be noticed on this band. Usually pretty reliable for, say, 100 miles in daylight in typical conditions, 500-1000 miles not being surprising after dark. See Wikipedia 80m band description^[7]. Antenna length less challenging than 160m but may still be an issue.

For communications where you only need to cover, say, 3 or 4 counties, 80m by day switching to 160m by night would be eminently practical and likely to be reliable even with suboptimal antennas.

40m Band

40m has some useful ground wave, extending to maybe 20-30 miles but is much more useful by sky wave, leading to noticeable skip effects where stations say 50 miles away are unreachable whilst 100 miles is fine. The band is fairly narrow and may be congested with powerful European stations making it hard to find a quiet frequency. During daytime it should be possible to cover most or all of the UK, after dark very much further including intercontinental contacts. See Wikipedia 40m band description^[8]. At 20m length a full-size antenna is more easily achieved and a shorter antenna is less of a compromise. If you are trying to contact someone but suspect that they are in the skip dead zone, switching to 80m may be the answer.

60m Band

This is not so much a band as a set of spot frequencies which have been allocated for amateur use relatively recently. Only holders of full licences have access to this band which is a shame as much of the time it's close to ideal for intra-country communications by day apart from the effects of skip. Use from moving vehicles is not allowed however it's permitted to speak to military stations which share the frequencies, when this happens it's usually cadets undergoing training rather than actual military exercises. Daylight contacts of 300 miles are quite normal: it can be quite odd to speak to someone with a very strong signal 200 miles distant but have someone only 40 miles away inaudible due to skip.

20m Band

Mentioned only for completeness, the skip on this band renders it of little use for local communications. It is, however, the primary band for intercontinental communication and if your interest lies in that direction it's well worth reading more about. There are other bands above 20m in frequency which come into use during the peaks of solar activity but are otherwise hit-and-miss.

Practical Installations

If there is room for a good antenna it's not hard to set up a very effective short wave amateur installation. There are numerous handbooks available advising on all aspects of amateur radio, for example the Radio Society of Great Britain Handbook^[9] which includes extensive advice on how to set up a multi-band short wave radio station. Many people very successfully operate radios on all of the bands mentioned above with a compromise antenna or even from moving vehicles. An internet search will also reveal a lot of advice.

Transceivers are widely available and tend to be aimed at the enthusiastic long-range devotee rather than the person looking to chat to locals on a budget, so the cost of new equipment can be surprisingly high. As of 2022, some more affordable entry-level options have started to appear but even so, unless buying second-hand gear, a budget of more than £500 is likely to be needed for the transceiver and antenna tuner. Home-made equipment is sometimes used but that's not available to those who only have a foundation licence. Used equipment sometimes comes on the market however transceivers hold their price well and do not usually resell at a steep discount to the new price.

If your goal is to have a set-up which can reliably provide voice communication with most of the UK most of the time using the amount of power permitted by a foundation licence, it's entirely possible with a mix of 160m, 80m and 40m. The modest power will occasionally be annoying but by no means a serious disadvantage.

Organised groups of amateurs will sometimes participate in field day sessions where the objective is head for a wild spot out in the countryside and set up a temporary station to see how many contacts can be made with other similar groups. A spot with a couple of suitable trees often allows an extremely good short wave antenna to be erected (which the help of a bow and arrow and some fishing line) and this also provides very good experience for anyone wanting to improve their effectiveness in emergency communications.

VHF and UHF Amateur Radio

For completeness it's worth touching on the two most common bands used that are not short wave: the 2m (145MHz) and 70cm (430MHz) bands. Nearly all the hand held radios talked about on the main communications page use frequencies close to the amateur 70cm band because using modern technology they are very easy to make at low cost and the short antenna that is required is less of a compromise. For historic reasons 2m falls into what is known as Very High Frequency (VHF) category and 70cm the Ultra High Frequency (UHF) category, nowadays generally lumped together as VHF/UHF because the distinction is archaic. The most common mode for voice communications is FM as it's cheap and easy to implement although some advanced and correspondingly expensive transceivers may also offer SSB and digital modes.

There is a number of Chinese-made hand held radios available for these bands such as the ubiquitous Baofeng UV5-R^[10] a hand held 2m/70cm radio which currently retails for under £30. Radios like these usually provide 100 or more pre-programmable channels which store wanted frequency, power levels, frequency split (for repeaters), CTCSS code (see below) and more. They are usually incredibly tedious to program through their keypads and it's usual to program them from a computer using a USB programming cable. A very popular free piece of software known as CHIRP^[11] is commonly used for this purpose although some manufacturers still insist on using proprietary software. If CHIRP doesn't support a particular radio, don't buy it is the advice, as there are plenty of alternatives!

Amateur use of these bands is typically not constrained by antenna or power restrictions so very effective antennas can be erected on top of poles or buildings, either omnidirectional or focused highly directional antennas which may be capable of rotation to point in any desired direction. These may also be coupled with high power up to the legal limit and with long-range modes such as SSB or Morse Code. From an advantageous location (line-of-site constraints apply to these bands, there is no reliable sky wave) highly reliable communications can be established over ranges of, say, 30 to 50 miles depending on terrain and considerably more if the terrain is benign. Although the antennas for 2m are larger than 70cm they are not an unmanageable size and 2m tends to offer up to double the practical range of 70cm for the same amount of power, it also tends to go further beyond the visible horizon due to diffraction effects. Neither band is at all affected by typical weather conditions.

A vehicle mounted dual-band 2m/70cm is both practical and fairly inexpensive to do, with some radios offering simultaneous operation on both bands or even cross-band operation, where a vehicle could be located on a high point and then used to relay a signal from a hand held radio on to the other band.

The simplicity of antennas, the lack of atmospheric noise and the wide range of low cost equipment means that for local communications most amateurs prefer these two bands. In many countries the bands are supplemented by repeaters located at high points with good antennas which simultaneously receive your signal on one frequency and retransmit it on another in the same band. From a cheap hand held radio it would be quite normal to use a repeater maybe 10 miles distant or from a vehicle as much as 30 or 40 miles distant, speaking to someone else within the repeater's range, so potentially 50 miles or more away. Repeaters are not always provided with backup power and only handle one conversation at time, which is not a problem for leisure use but more of an issue for emergency or grid-down situations.

In the UK repeaters identify themselves by transmitting a Morse Code call sign (sometimes also synthesised voice ID) and usually follow this with a single letter to identify their CTCSS code. CTCSS is a sub-audible tone transmitted along with your voice and must be present to turn the repeater on, it's used so that if you are in range of several repeaters on the same frequency, the CTCSS tone indicates which one you intend to use. CTCSS is universally supported by modern equipment although some vintage radios may not have it available, something to watch out for. Generally speaking you will only be in range of one repeater on a given frequency as frequencies are allocated geographically to avoid congestion and you would program your radio to use the expected CTCSS code for that repeater on that frequency, to suit your locality. Occasionally under what is known as 'lift' conditions the typical 40 mile range of a band (especially 2m) may suddenly extend to hundreds of miles resulting in you being able to hear repeaters far away. Lift conditions may make French and Dutch repeaters easily audible from central and eastern England for a few hours or a day or two. These kind of lifts are not usually Sun related but mostly due to high-pressure weather conditions and temperature inversions in the lower atmosphere leading to bending of signals and 'ducting'.

Amateurs operating well-equipped stations from their homes will often use repeaters as a form of social network. Whilst they could probably communicate with each other directly and not use the repeater, the repeater can act as a social hub and a receiver will often be left listening to it in case a friend or regular contact appears. A conversation might then take place via the repeater (with an implicit invitation to others to join in) or for matters that are only of individual interest a switch to a non-repeater frequency might be made if direct communication is possible.

Repeaters are important infrastructure. They are usually owned by a radio club or group and funded by subscription whilst being made freely available to anyone who wishes to use them. Some clubs or repeater groups may have a policy that emergency communications takes priority through their repeater, however unless you are a member of their group it's unlikely that that policy will apply to you without prior agreement. If you regularly use a local repeater, consider contributing to the running costs and joining the group as a member. You will make new friends that way and will probably find shared interests.

Amateurs also have access to a 50MHz (6 metre) band which tends to be highly under-used. There is a small number of 6m FM repeaters in the UK. Equipment for 6m is less widely available but still easy to find and for reliable communications that must go further than 2m, 6m may be a viable option, providing some 50% to 100% further reliable range. Antennas are, of course, three times the size of 2m equivalents and on vehicles tend to be a compromise (but still only half the size of a CB antenna), so 6m is maybe best suited to fixed rather than mobile stations. If a group wished to set up a 'private' network of 6m stations to talk to one another it would certainly remain unnoticed by the majority of other amateur users even though true privacy is not available. 6m is at times subject to extraordinary lift conditions permitting worldwide communication which is very exciting to some amateurs but this cannot be relied on.