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Charity Number: 1008250
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Patron: Lord Montagu
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P.M.R. OperationOkay, so you've read and understood Chapter 1. You've followed Chapter 2 and now you have a working P.M.R. - now what? This chapter will discuss how you communicate with other people on the radios, and walk you through the radio procedures. Radio Procedure is simply a defined system of planning, using and talking over the radios in a way that makes best use of them. The ReasonsWhen a group of people are operating radios together, it soon becomes clear that some form of structure is required. This is mainly due to limitations of the radios. The best way to envisage these limitations is to compare the situations of a boardroom and a lounge chat. In a lounge chat, everyone sits around and if someone wants to talks they simply speak up. This is possible because the rest of the room can hear many different sounds, and then choose which one to listen to. In a boardroom, where everything has to be recorded for posterity, the person taking minutes can only write one word at a time. Because of this, people have to take it in turns, and ask for permission before talking. Using radios is like being the boardroom recorder. You can only listen to one sound at once, so everyone has to behave in an orderly manner, getting permission before speaking and then doing so clearly and quickly. These limits are caused by two basic problems. These are "dupliexing" and what I call "The big mouth syndrome". DuplexingDuplexing is the fancy name for transmission flow control. The simplest duplex is simplex. With simplex radios you have one radio that can only transmit, and you have other radios that can only receive. An example of simplex transmission is you sat at home listening (receiving) to the breakfast show on BBC Radio 1 (transmitting). Right at the other end of the Duplex ladder is Full Duplex. With Full Duplex radios can transmit and receive at the same time. They do this by using one frequency to transmit and another frequency to receive. Because of the big mouth syndrome Full Duplex only really works between two points. An example of Full Duplex is mobile phones. They transmit to a zone mast on one frequency, and the mast transmits back on another frequency. All the clever stuff like connecting to the phone system is done at the mast end. Half Duplex sits nicely in the middle of Simplex and Full Duplex. With Half Duplex, all radios can transmit and receive, but not at the same time. For half duplex transmitting and receiving are both done on the same frequency. The Big-Mouth SyndromeThe eloquent term "Big Mouth Syndrome" nicely describes the other main limitation on Radios. As we all know, if two people are having an argument, it is not the person who is correct who wins, but the one with the biggest mouth. Similarly, with radios, it is not necessarily the person you wish to listen to that you will hear, but the one with the strongest signal. Radios can only receive one signal at once, and any other signals at the time will simply be ignored.
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