What is amateur radio?

Amateur radio involves the use of radio waves to communicate and make friends with other amateurs around the World who happen to be on the air and within range.

Unlike a mobile phone you do not need to know the number or the person in order to make contact, and unlike the Internet there is a universal shorthand that can be used to communicate basic greetings and information independent of the local languages. Also unlike both the mobile phone and the Internet, there is nothing to pay after the initial outlay.

Communication can be made by voice, text, or with pictures. It brings together basic physics, electronics, computing, photography, and radio etiquette.

The communication range can be increased in a number of ways e.g.

• Relaying the signal via the local repeater stations positioned on hills (50km range).
• Relaying the transmissions via the amateur satellites orbiting the Earth (5000km range).
• Bouncing the transmissions off the ionised layers above the Earth which are excited by the rays from the sun (up to 20 000km range).
• Other methods include bouncing the transmissions off meteor trails in the atmospere, and even off the moon (780 000 km round trip!)

However the satellites are too low to be in stationary orbit and only appear above the horizon for 5 to 20 minutes at a time. Also, the characteristics of the ionised layers above the Earth are very changeable depending on the frequency in use, the time of day, the season and the sunspot cycle. Skill is therefore required to make the best use of the prevailing conditions - you can never be sure which countries you can reach and who you can make contact with at any particular time. This is the continuing challenge of radio, and explains why there are so many modes of transmission in use and in development.

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Is it like CB?

It is a little bit, the best thing about the Citizens Band, and the main reason it was introduced as an alternative to amateur radio, is that the CB user needs little or no technical knowledge or expertise in order to successfully operate CB.

CB can be used for work and play and is ideal where two or more people wish to keep in touch within a 6 to 12 km range. The conversations are free and it is possible to talk to numerous people in a group at the same time. It is a useful resource if you are involved in activities such as caravaning and camping clubs, off road driving, boating and fishing, or simply want to keep in touch with a group of friends or aquaintences.

Amateur radio on the other hand, whilst restricts your contacts to thousands of other amateurs for non-commercial purposes, makes communication possible over large distances as well as short openning up the whole world for free.

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Modes

A number of different 'modes' co-exist to enable radio amateur transmissions to carry the required information because each has its own advantages and disadvantages. The most common types in use are summarised below:-

• CW Continuous Wave - The transmitter output signal is unchanged except for being switched on and off to send Morse code. This uses the simplest type of transmitter but requires a receiver with the facility to convert steady radio frequency into an audible tone (Bandwidth 250Hz).
• AM Ampitude Modulation - The transmitter uses the audio signal to vary the strength of the transmitted signal (analogous to rapidly turning the volume control). The transmitter is moderately complex but the receiver uses the simplest type of demodulation to extract the sound at the receiver (Bandwidth 6kHz).
• NBFM Narrow Band Frequency Modulation - The transmitter uses the audio signal to vary the frequency (analogous to rapidly turning the tuning control). The transmitter and the reciever are moderately complex but can deliver noise free sound if the signal is sufficiently strong (Bandwidth 11kHz and 16kHz).
• LSB Lower Sideband - Amplitude modulation results in the information about the sound being carried in two duplicate narrow bands situated either side of the central transmitter frequency (carrier). Here the lower side band is sellected for transmission and the carrier and upper sideband removed. This makes the best use of the transmitter power rating and also reduces the overall bandwidth. It requires complex transmitters and receivers and careful tuning of the receiver (Bandwidth 2.7kHz).
• USB Upper Sideband - Similar to the LSB mode except that the upper sideband is selected for transmission instead.
• FSK Frequency Shift Keying - This is a method of sending digitised information where a '0' is represented by one tone and a '1' by another. Some schemes use multiple tones so that bytes of information can be sent at the same time. This can give a warbling sound to the signal. Free software is available to encode and decode the information which may be voice, text or pictures.

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