Highly Resilient POCSAG Radio Paging - Everything You Need To Know

Added: 2026-05-15

[00:00:01]Personal pages were mainly used only by people in the business world in the early days. But by the 1990s, pages became a popular means for almost everyone to keep in touch with one another. Even school children had pages on their belt so that they could keep in touch with their parents and friends.

[00:00:17]Pages were regarded as the porpa's mobile phone. They were cheap to buy and use, but inflexible. Paging was seen as something that would be killed off by cheap mobile phones and it was for the most part, but it's still widely used today by many users. There is a national transmitter network across the UK which broadcasts high power signals that reach every corner of the UK. Pages are still widely used by the emergency services along with hospitals, private healthare companies, alarms, security, and a whole host of other users. You can use a simple device like this link in the description or a laptop with software link in the description to receive these pager messages in 2026. I have to insert a disclaimer here. It's illegal according to the Wireless Telegraphy Act to receive any signal not intended for you. This video is purely for educational purposes. The main format still around in the UK is POXAG. This is my introduction to POXAG.

[00:01:15]POXAG stands for the Post Office Code Standardization Advisory Group. It's a digital paging scheme that was developed by the British Post Office or BO to provide a standard signaling format for the UK. It went on to become the most common paging formats here. In the late 1970s, the World Market for wide area radio pages only required a few manufacturers, most of which invented their own radio signaling codes. This meant that operators of radio paging services, for example, the British Post Office, were limited to a single source of supply for pages or were faced with making limited ad hoc arrangements to deal with the situation. The BO public radio paging service opened in London in the 1970s. It was designed with special features that enabled it to operate with a mixture of types of paging codes. The receivers were small enough to be clipped into the pocket and gave a high-pitched 10-second bleep when activated by a simple phone call over the ordinary public telephone network.

[00:02:10]This worked satisfactorily, but it was expensive and a very limited number of code formats could be accepted by the BO before the waste of transmission time inherent in changing from one type of code to another became excessive. The BO was faced with two options. It could either limit the number of types of code formats in the national system or develop a completely new standard code format. Manufacturers and their professional associations all had a meeting. This led to the formation of the post office standardization advisory group, also known as the POXAG.

[00:02:43]The group produced a set of requirements for a new paging format in 1976.

[00:02:48]The code capacity had to accommodate 1 million pages with up to four addresses per pager. The preferred number of users in the most popular zones of the UK national system was at least 120,000.

[00:03:00]The paging rate had to be greater than six calls per second, so a target of 10 calls per second was chosen. The 153 MHz band was selected for use in the UK, but the code had to be usable on any radio frequency that might be allocated to radio paging in the future.

[00:03:16]A radio channel bandwidth of 25 kHz was allocated to the BO radio paging service. The code had to be usable in a 12.5 kHz bandwidth radio channel. Any type of modulation was considered suitable provided that it contributed to a cost-effective solution. A lost call rate of less than 2% at the edges of any proposed transmission area or typical urban radio environment was considered acceptable. It was agreed that the false call rate due to unrejected transmission errors should not exceed 1 in 100 million.

[00:03:48]For the great majority of calls, the time from the receipt of the last digit in the control terminal to the completion of transmission in all zones was required to be less than 2 minutes.

[00:03:58]It was concluded that the ability to convey messages, for example, the name or telephone number of the call originator was a feature desirable for future use, but that the provision of this feature should neither add appreciably to transmission costs nor add to the cost of pages designed to receive an address only. And finally, to provide national coverage using a single radio channel was a necessity.

[00:04:21]A review was made by the Poxag of all likely codes known to have been adopted by manufacturers or postal, telegraph, and telephone administrators who were operating public radio paging services.

[00:04:32]None of these existing codes met all basic requirements, nor were they fully acceptable to the majority of members of the Poxag. It was therefore necessary to develop a new code format. Several original code formats were proposed and rejected. Eventually, Mr. P maybe of Philips Research Laboratories conceived a basis of the standard code format and his proposal was welcomed enthusiastically. Some small modifications to improve its performance characteristics and to increase its capacity and battery saving capabilities were also included. Poxag was renamed CCIR radio paging code number one or RPC1, but the old name seems to have prevailed. It was officially recognized in February 1981.

[00:05:16]Poxag is based on digital signals.

[00:05:19]Depending upon the type of pager used, different digital signals can be sent.

[00:05:23]Voice is not supported. Some tone only pages activate when they receive a signal. With tone only pages, you usually had to call your pager service provider to find out what the message was. Numeric pages enabled people to receive numeric information like telephone numbers they could call in order to talk to the person trying to contact them. Alpha numeric pages then allowed people to receive and display text messages such as emergency information, jobs, news, and anything you can think of. Some people even had their emails directed to their alpha numeric pager so that they could read their email on it. Poxag signals are sent in a modulation technique known as FSK or frequency shift keying. The carrier wave is shifted up or down from the center frequency by 4.5 kHz and these shifts represent the data being sent. The high frequency represents a zero and the low frequency a one. The 4.5 kHz frequency shift is used with a 25 kHz channel spacing. Some jurisdictions require that all systems move to 12.5 kHz channels and 2.5 kHz frequency shifts. FSK offers good noise immunity and is inexpensive to generate.

[00:06:32]However, FSK is not suitable for high data rate transmission.

[00:06:37]The most common board rates used by Poxag pages are 512 board, 1200 board, and 2400 board. Poxag originally transmitted at 512 bits per second only.

[00:06:48]It offered the best reliability and transmission range. Faster transmission at 1200 or 2400 bits per second came later. This is known as super poxag and has mostly replaced poxag. Higher board rate paging enabled higher message capacity and speeds.

[00:07:05]Paging base stations transmit pages simultaneously within a service area.

[00:07:10]Every message sent to a subscriber is transmitted by the entire network. It has to be because the subscriber could be anywhere. Messages are sent in batches and each pager address is located in a specific frame within a batch within the assigned frame. The pager will look for the message. The pager after detecting the preamble and synchronizing to the frame sync code word turns off its receiver circuits until the proper frame appears. This increases the life of the pager battery.

[00:07:37]Poxag pages support tone, numeric, and alpha numeric messages. Voice is not supported.

[00:07:44]We need to look into the transmission structure in more detail. It's extremely complicated, but I'll explain the top line as simply as I can. The poxag transmission structure is as follows.

[00:07:55]Each transmission starts with a preamble to enable conservation of battery power by the use of sampling techniques and to allow easy acquisition of bit synchronization by the pages. The preamble is a pattern of reversals 1 0 1 0 1 0 repeated for a duration of at least 576 bits. This basically wakes up the pager so it's ready to receive a page. The preamble indicates the start of the transmission and indicates the board rate at which the page is being sent.

[00:08:24]The page data is transmitted immediately after the preamble in what are known as batches which contain one frame synchronization code word and eight frames. The synchronization code word looks like this. Each batch of eight frames is preceded by a frame synchronization code word.

[00:08:42]Each frame contains two code words. Two types of 32bit code words can be transmitted within each frame. the address code word which always starts with a zero and a message code word which always starts with a one. An address code word contains 18 bits of addresses and two function bits.

[00:09:00]Function bits are used in different ways depending on the system.

[00:09:05]Each message code word contains 20 bits of data. Both code words end with a 10 bit BCH error correction code and an even par bit which is an error detecting code.

[00:09:17]After the preamble and frame synchronization code word, the pager looks for its cap code in an address code word. After an address code word, one or more message code words follow which contain the message contents for the pager. Longer messages are spread over multiple code words.

[00:09:34]So what is a cap code? CAP stands for channel access protocol. It's a unique ID assigned to a pager. Early pages could only be programmed with one cap code, but modern pages can support multiple cap codes. They can be assigned to multiple pager receivers to allow group paging.

[00:09:52]The Poxag standard has been the most successful standard, possibly because it's nonproprietary and has an extremely simple protocol. It has many advantages.

[00:10:01]It can cover extremely large areas and penetrate buildings with ease. This is one reason the emergency services still use it in the UK. Messages are transmitted reliably to crews in remote locations without cell service or airwave connectivity. It's cheaper than using cellular networks. Pages use very little power and so a single battery can last many months. Pages are untraceable, meaning nobody can tell where the recipient is.

[00:10:28]Although paging is more resilient than other forms of mobile communication because it can penetrate buildings, there's no guarantee that a message has reached its destination. Some companies offered the retransmission of messages at set intervals, but few did, and those that did charged extra. Poxag is relatively slow by today's standards.

[00:10:47]2400 bits per second seems space age 40 years ago, but it restricts the type of services that could be provided. A shortcoming of Poxag is that its data rate is relatively low and therefore its capacity is low. Its limitations became more conspicuous as the number of users began to grow.

[00:11:05]Unlike GSM phones that could roam abroad by the 1990s, pages usually had to be used in the country they were bought in, you couldn't take your poxag pager from the UK and expect it to work in another country. Later on, newer technologies allowed people to take pages to places like the United States. Euro message came in in 1990 which provided crossber paging in the UK, France, Italy, and Germany. BT, Airall, Raikal, Voda Page, Intercity, and Digital were all granted a license to operate on UHF for this service.

[00:11:38]In the 1990s, new paging codes were developed that offered higher data transmission rates and other advanced features such as European and network roaming. Competing protocols including Hermes and Flex were developed to achieve higher capacity.

[00:11:53]There are poxag frequencies in use in the UK, Germany, Spain, Sweden, Switzerland, Belgium, Italy, France, the United States, Mexico, Colombia, and Australia. To keep this video shorter, I'll only show the UK frequency allocations. The allocations for the countries I mentioned are all available with a simple Google search. 26 decimal 580 MHz was allocated for local area pages mainly hospitals for both Poxag and other voice systems. 49 to 49 decimal 4875 MHz was spread across 40 channels mainly used by hospital poxag systems.

[00:12:32]137 decimal 9625 to 138 decimal 2125 was used by Mercury paging which later became page one.

[00:12:42]153 decimal 025 to 153 decimal 5 was used by page 1 B2 paging Voda page readyon air call and RNLI lifeboats to name a few b2 paging closed in 2004 and customers were moved to page one closed its paging network used by just a thousand customers in 2017 439 decimal 9875 is used for the dapnet amateur radio paging ing service 454 decimal 025 to 454 decimal 8250 was allocated to hospitals airall emokco and millcom to name a few6 decimal075 was used by hutches and paging which became orange closed hutches and paging in 2000 some other large companies that spring to mind are life page used by the NHS intercity paging page boy communications multi-one paging Milliccom, Digital, Blick International, and Capital Radio Paging. If you know of any more, leave a comment below.

[00:13:51]Page One is the UK's remaining national poxag service provider. To my knowledge, it maintains that its service remains the most reliable and cost-effective way of sending out thousands of messages at a time with far greater coverage than the mobile phone networks. The fire and ambulance services use them widely with the NHS accounting for around 10% of use with 130,000 doctors still using them while on call. Mobile reception is patchy in hospitals and so pages are ideal in emergency situations.

[00:14:20]153 decimal 350 megahertz is the UKwide frequency for page one and is extremely busy with traffic every few seconds.

[00:14:28]On-site pages can be found in some of the other frequency allocations too.

[00:14:33]While subscribers might believe their messages are private, this is not the case. Poxac messages are transmitted in unencrypted ASI and can be accessed by anybody with access to a radio scanner or a laptop with the relevant software.

[00:14:46]Because messages are broadcast by paging transmitters up and down the country, messages from everywhere can be received everywhere. Years ago, people used to put a discriminator tap on their scanner, which takes a partially de modulated signal and routts it to an external device such as a computer in order for software to decode pager signals.

[00:15:05]PDW was released in 2003, which runs on a computer and decodes poxag and flex pager signals to name just two. You can also use something like a hack RF, similar to what I've shown you in this video, to decode poxag signals in one simple unit. Not that you should