Walkie talkies

walkieNomadic networks and the walkie-talkie
Walkie-talkies are transmitters/receivers that can send and receive voice signals in the form of radio waves. A handset is typically a little bit bigger and heavier than a mobile phone and you can usually see a short aerial sticking out of it. Unlike cellular phones, you cannot talk and listen at the same time. You can only do one or the other and for this reason walkie-talkies are an example of half-duplex communication. You’ve probably seen people using walkie-talkies on TV - they keep saying “Over” when they have finished talking, to signal to the other person that it is their turn to speak.

Radio frequencies
There are a fixed number of radio frequencies that are available in any country. Some frequencies are reserved for TV and radio and some are reserved for mobile phone use. For a mobile phone company to operate, they must buy the right to use certain frequencies. They can then have exclusive access to them and no other company can use them. In this way, one company’s phone calls will not interfere with another company’s. There are some frequencies, however, that are public. In Europe, there are 8 public frequencies that can be used by anyone. You do not require a licence to use them. Within each of the eight frequencies, there are 38 ‘bands’ that can be used, making a total of 8 x 34 or 304 different communication channels. Manufacturers of walkie-talkies make use of these public communications channels in their products and for that reason, the communications are not secure - the chat across them can be heard by anyone listening in!

Uses of walkie talkies
Walkie-talkies can form an ideal communications network in certain circumstances. They can have a range of up to two miles depending on the model you buy and are ideal for security personal to keep in touch in shopping centres, clubs, festivals or on a factory site, for example. They could be used to keep key people who could be working anywhere in a building in touch with reception. A Network Manager looking after a computer network, for example, or a maintenance person, could be anywhere in a building but may be needed at short notice. They would be ideal candidates for a walkie-talkie.

Pros and cons of walkie-talkies
Walkie-talkie handsets are cheap to buy and you don’t need to then rent a phone line or airtime or buy a SIM card or contract from any company. Handsets use rechargeable batteries so are cheap to run and they are small and highly portable. We have already said that they don’t need to be licensed and a company can have as many handsets as they like using whatever public frequencies they like. Because the handsets use public frequencies, however, anyone can tune in to your conversations so they are not suitable for sending secure messages. Their limited range may be a problem for some applications.

Q1. What is meant by half-duplex communication.
Q2. There is a type of communication called 'simplex' transmission. Find out what this means and an example of this type of communication.
Q3. What do people often say after speaking on a walkie-talkie?
Q4. How many public frequencies are there?
Q5. How many bands are there in each frequency?
Q6. What sort of range do walkie-talkies have?
Q7. Describe some of the advantages and disadvantages of walkie-talkies compared to mobile phones.

Extension task
Look at walkie-talkies you can buy from various websites. How much do they cost compared to mobiles? Are they bigger / smaller generally compared to mobile phones? Are they as stylish? What sort of features come with walkie talkies? What features are missing compared to mobile phones? What sort of ranges do they have? How long can they run between charges?