Pagers were very popular in the 90s. At that time I was a student, and a pager for me was something like a Star Trek communicator, a piece of advanced technology. It's funny to think about it because now I know that technologically, the paging protocol is very simple. In terms of coding, a pager is not that different from the wireless doorbells that are currently selling for $5 on Aliexpress.
Even though pagers are no longer used everywhere, some people still have them in their homes. Is it possible to test a pager now? Definitely, and I'll show you how to do it. Let's get started.
Even though pagers are no longer used everywhere, some people still have them in their homes. Is it possible to test a pager now? Definitely, and I'll show you how to do it. Let's get started.
POCSAG - the protocol for messaging
Suppose we want to send the message "TEST" to the number "one thousand two hundred and thirty-four". In binary form, it will look something like this:
The bits are encoded using frequency-shift keying (FSK) modulation, using a bandwidth of 9 kHz and a speed of 1200 bits per second, the whole message is transmitted in about 0.5 seconds.
It looks simple, and it is. I will skip the details; those who are interested can read the protocol specification. All of these bits can be easily written even on paper - in the past, these protocols were simple, which is not the case with modern GSM or Wi-Fi.
There is no authentication or security keys in POCSAG messages - all messages for all customers of the paging company are available on the air "as is" and, incidentally, can be easily decoded using PC software such as PDW.
How do customers receive their messages? Each pager has a unique identifier called CAP - Channel Access Protocol, or RIC - Receiver Identification Code. All pagers from a paging provider listen to the same frequency, say 164 MHz. If the code in the message is the same as the pager code, the pager saves the message and emits a loud beep. That's all. The communication is one-way, there is no return confirmation, the pager has only a receiver and no transmitter at all. The logic and hardware are extremely simple, so the pager can operate for more than a month on a single AAA battery. Interestingly, pagers are still used in some countries even now - in hospitals or emergency services, where it is important to have a portable and lightweight device with a long battery life.
Rpitx
The easiest way is to use a Raspberry Pi, and surprisingly, it's completely free: with the free open-source rpitx software, a signal can be generated directly from the Raspberry Pi pin. It is enough to put a short wire on the GPIO4 pin:
The pager is sensitive enough to receive such a signal at a distance of several meters. To send a message, we need to install the rpitx software and run the command:
Here 1000001 is the capcode, 465198000 is the frequency, and 0 is the message type (the message can be one of 4 types, for example, 0 is numeric only, 3 is alphanumeric). Other parameters, such as signal inversion or baud rate, can also be changed if necessary. The output power is definitely not high, but it is enough to test the pager in the apartment. The rpitx app works surprisingly well for its (zero) price, but of course, the Raspberry Pi as a whole is not an accurate RF oscillator. The frequency may not be 100% correct, and a small value correction in the range of a few kilohertz may be required (it is also good to have an RTL-SDR as a reference receiver).
Conclusion.
It was fun to test the paging and explore how it works.
It's also interesting to note that vintage devices are fun to test, and they look cheaper at first glance. But in reality, they are not. For various tests, I bought 3 pagers for $20-30 each. But the first pager had an incompatible frequency, the second was password protected and I couldn't change its settings, and only the third one worked. Instead of these three used pagers, I could have bought one new one.
It is also obvious that there is no guarantee when you buy things from 20 years ago - even if the seller writes "tested" in the description, the most he did was put in a battery and check the logo on the screen. I don't expect sellers to know about frequencies or access codes. But in my case, it was done for fun and self-education, so I don't have a problem with that, even if something doesn't work.
Another problem I encountered when testing pagers is "link extinction". Everyone used to think that "Google knows everything" and "information on the Internet is free," but in fact it is not. Storing files and hosting sites costs money, and after a while web pages become inaccessible. Many old forum posts have dead links and contain empty squares instead of images. When trying to find information about old things, all this became obvious. I was able to find useful software on some old and abandoned web pages, but there is no guarantee that these links will be alive for a long time.
There may also be legal reasons, for example, I'm not sure that Motorola has officially authorized anyone to publish software for programming their pagers, even if the publication is from 25 years ago. But it can be important to preserve technical heritage to preserve such things. Finally, pagers can be tested, and that's fun.
For those who want to conduct more tests on a larger scale, it is also possible to use POCSAG on amateur radio frequencies and join a network to receive DAPNET (Decentralized Amateur Paging Network) radio transmissions. This will require a license to receive radio transmissions, but for those interested in digital communication, it may be worth obtaining. I wish all readers good luck and interesting experiments!
Despite the age of this type of communication, pagers are still in use. But while 20 years is already a respectable age for technology, it's not even youth for programming languages. For example, C++, created by Björn Straustrup back in 1983, is still in the top of the most popular languages in the world thanks to its clean and beautiful logic and flexibility. If you want to diversify your Skill set with this language, pay attention to our C++ development course, because this language has been and remains no less important than English for millions of programmers.
Suppose we want to send the message "TEST" to the number "one thousand two hundred and thirty-four". In binary form, it will look something like this:
The bits are encoded using frequency-shift keying (FSK) modulation, using a bandwidth of 9 kHz and a speed of 1200 bits per second, the whole message is transmitted in about 0.5 seconds.
It looks simple, and it is. I will skip the details; those who are interested can read the protocol specification. All of these bits can be easily written even on paper - in the past, these protocols were simple, which is not the case with modern GSM or Wi-Fi.
There is no authentication or security keys in POCSAG messages - all messages for all customers of the paging company are available on the air "as is" and, incidentally, can be easily decoded using PC software such as PDW.
How do customers receive their messages? Each pager has a unique identifier called CAP - Channel Access Protocol, or RIC - Receiver Identification Code. All pagers from a paging provider listen to the same frequency, say 164 MHz. If the code in the message is the same as the pager code, the pager saves the message and emits a loud beep. That's all. The communication is one-way, there is no return confirmation, the pager has only a receiver and no transmitter at all. The logic and hardware are extremely simple, so the pager can operate for more than a month on a single AAA battery. Interestingly, pagers are still used in some countries even now - in hospitals or emergency services, where it is important to have a portable and lightweight device with a long battery life.
Rpitx
The easiest way is to use a Raspberry Pi, and surprisingly, it's completely free: with the free open-source rpitx software, a signal can be generated directly from the Raspberry Pi pin. It is enough to put a short wire on the GPIO4 pin:
The pager is sensitive enough to receive such a signal at a distance of several meters. To send a message, we need to install the rpitx software and run the command:
Here 1000001 is the capcode, 465198000 is the frequency, and 0 is the message type (the message can be one of 4 types, for example, 0 is numeric only, 3 is alphanumeric). Other parameters, such as signal inversion or baud rate, can also be changed if necessary. The output power is definitely not high, but it is enough to test the pager in the apartment. The rpitx app works surprisingly well for its (zero) price, but of course, the Raspberry Pi as a whole is not an accurate RF oscillator. The frequency may not be 100% correct, and a small value correction in the range of a few kilohertz may be required (it is also good to have an RTL-SDR as a reference receiver).
Conclusion.
It was fun to test the paging and explore how it works.
It's also interesting to note that vintage devices are fun to test, and they look cheaper at first glance. But in reality, they are not. For various tests, I bought 3 pagers for $20-30 each. But the first pager had an incompatible frequency, the second was password protected and I couldn't change its settings, and only the third one worked. Instead of these three used pagers, I could have bought one new one.
It is also obvious that there is no guarantee when you buy things from 20 years ago - even if the seller writes "tested" in the description, the most he did was put in a battery and check the logo on the screen. I don't expect sellers to know about frequencies or access codes. But in my case, it was done for fun and self-education, so I don't have a problem with that, even if something doesn't work.
Another problem I encountered when testing pagers is "link extinction". Everyone used to think that "Google knows everything" and "information on the Internet is free," but in fact it is not. Storing files and hosting sites costs money, and after a while web pages become inaccessible. Many old forum posts have dead links and contain empty squares instead of images. When trying to find information about old things, all this became obvious. I was able to find useful software on some old and abandoned web pages, but there is no guarantee that these links will be alive for a long time.
There may also be legal reasons, for example, I'm not sure that Motorola has officially authorized anyone to publish software for programming their pagers, even if the publication is from 25 years ago. But it can be important to preserve technical heritage to preserve such things. Finally, pagers can be tested, and that's fun.
For those who want to conduct more tests on a larger scale, it is also possible to use POCSAG on amateur radio frequencies and join a network to receive DAPNET (Decentralized Amateur Paging Network) radio transmissions. This will require a license to receive radio transmissions, but for those interested in digital communication, it may be worth obtaining. I wish all readers good luck and interesting experiments!
Despite the age of this type of communication, pagers are still in use. But while 20 years is already a respectable age for technology, it's not even youth for programming languages. For example, C++, created by Björn Straustrup back in 1983, is still in the top of the most popular languages in the world thanks to its clean and beautiful logic and flexibility. If you want to diversify your Skill set with this language, pay attention to our C++ development course, because this language has been and remains no less important than English for millions of programmers.
