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Licence free

Purpose

Limitations

Limited range

Equipment restrictions

The PMR446 band has many channels

Licence free

The UK Private Mobile Radio 446 specification defines type approved radio transceivers and aerials.  The public can buy and use any radio transceiver which is type approved to the PMR446 specification.  Such radios use a UHF band of 8 radio channels.  Such PMR446 radios can also be legally used in some other European countries.

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Purpose

PMR446s can be used by the public for recreational purposes and by companies for business purposes.  They can be used by huge men in dark uniforms with silver buttons and also by small girls with pigtails, freckles and pink dresses.

The concept of licence-free means that almost anybody can use these radios for almost any purpose.

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Limitations

As there are only 8 radio channels and zillions of people in the UK who own PMR446s, there could be a problem in trying to get a word in edgeways.  The huge men in dark uniforms with silver buttons may think that they are more important than the small girls with pigtails, freckles and pink dresses.  They aren't.

Anybody (especially a business) who uses PMR446 radios must realise that anybody in range can hear what is said and that nobody has an exclusive right to use any of the 8 channels.  While using your radio, others may suddenly appear on "your" channel.  Tough.  If you don't like it, pay 1,000 for a pair of PBR radios.

There are only two ways in which such a licence-free system can work.  The first is to severely limit the radio range of every radio.  The second is for users to accept that the channels are shared and to try not to use a channel which is already in use.

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Limited range

Asking an expert the range of a particular radio system often results in a very vague reply.  It isn't because of lack of knowledge.  It is because many things can alter the range.

PMR446s are often advertised as having a maximum range of one or two miles.  In the UK, laws state that advertising must be honest, accurate and not misleading.  PMR446s therefore do have a maximum range of a mile or two.  On a sunny day.  With the wind behind them.  As long as you use them whilst standing on one leg and holding your left finger in your right ear and winking.  At other times, they couldn't transmit themselves out of a wet paper bag.

Situations which could severely limit the range include being in a building, in a street with tall buildings, among trees and among crowds of people.  Being inside a car does diminish the range slightly, but not severely.

The PMR446 range is therefore between one hundred yards and two miles.  If you can see the other radio, you can probably talk to it.  If you can't see it, you may or may not be able to talk to it.

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Equipment restrictions

Like all type approved equipment, it isn't type approved any more if you modify it.  The PMR446 specification is a maximum of 0.5 Watts of effective radiated power.  If the aerial has a gain of 1, its transmitter can have a power of 0.5 Watts.  If the aerial has a gain of 10, the transmitter must be only 0.05 Watts.

The European PMR446 licence-free specification says that the radios can't have the facility to connect to huge aerials as that would increase their range.  Legally, you can't even delve inside the radio to connect a pair of headphones from the loudspeaker connections as that would be modifying the radio and it would no longer be to specification PMR446.

PMR446s therefore have a built-in aerial and no socket to which an external aerial can be connected.  They may or may not have sockets for an external microphone or headphones.  PMR446s linked via the internet connect via the provided microphone and headphone sockets.

Radios must only be of the hand portable variety.  They can't be the mobile radio variety.  They can still be used in cars.

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The PMR446 band has many channels

But previously it said that there are only 8 channels? It depends on what you understand by the term "channel".  There are 8 radio channels, which means there are 8 radio frequencies with a bandwidth for speech.  Within a small distance, there can be only 8 simultaneous exclusive conversations.

The use of CTCSS can appear to provide more channels, but it doesn't.  What it does do is provide the convenience of appearing to have more channels.  It doesn't really matter what CTCSS stands for as long as it works.  In case you want to impress your friends with official geek radio gobbledygook, it is Continuous Tone Coded Squelch System and is sometimes called sub-audible tones.  If you use the hyperlink at the bottom of this page, you'll see that Ofcom believes that CTCSS stands for different words.

If a PMR446 radio has CTCSS, it transmits a secret inaudible sound whenever somebody speaks on the radio.  Pedants may say that a sound can't be inaudible as that is an oxymoron.  What these morons don't know is that CTCSS has existed for years and it works.

If the receiving radio also has CTCSS and is using the same secret inaudible sound (sorry about this), the loudspeaker works as expected and the voice at the transmitter end is heard.  "So what?", you ask.  Well the use of CTCSS in an area of heavy PMR446 usage can improve things.

Suppose that you are in a park where a local pop group will be giving a free performance.  There is an audience of 1,000 people.  Many are parents who have a PMR446 and have given their children a PMR446 so that they can run about in the park whilst still keeping in contact with Mam and Dad.  Suppose that 50 adults have radios and 50 children have radios.  At any one time there is a possibility of requiring 50 simultaneous radio conversations but there is only the possibility of 8 simultaneous conversations.

This can work if they all take it in turn to have their conversations such as, "Come back to your seat. The band starts playing in 10 minutes.", "Certainly Daddy dear.  And I will bring you an ice-cream which I bought with that 20 note which you gave me."  It is likely to be quite messy, but it can eventually work.

If all of the 100 people are using PMR446 channel 1 because that it what they normally use, it could take a while and the band will have stopped playing and have been in the pub for hours before all of the kids get all of the messages.

If a random spread of channels and a random spread of CTCSS tones (but the CTCSS tones must be in pairs) is used, things may sound better. Instead of everybody hearing anybody else who is using the same channel, they only hear anybody who is using both the same radio channel AND the same CTCSS tone.

If you think that the channel is free to use as you hear nothing, when you press the transmit button, you won't actually transmit if your radio is receiving a signal at the time.  This stops you interfering with other people's signals and vice versa.

CTCSS using the same sub-audible tones at the transmit end and the receive end can give the appearance of having many channels.  It certainly prevents you having to listen to other users of the same radio channel.  It can also merely mask the fact that the radio channels are in heavy use as you can't hear anything.

CTCSS is of most use with light or medium radio traffic.  With heavy radio traffic conditions, as you can't hear all the other stations, you won't realise why your friend, colleague or relative isn't answering you.

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Ofcom PMR446

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Page updated on 09 January 2017

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