First Czechoslovak radiotelephone networks: AMR
Czechoslovakia did not participate in the development of international mobile networks in the 1970s, the isolation caused by the iron curtain and Russia’s policy towards non-socialist countries was a clear separation of socialist countries from the problems of Western mobile networks. Moreover, during the seventies and quite distinctly in the eighties, there was an outdated socialist industry which, especially in the price-sensitive field of electronics for ordinary (ie non-military) use, was unable to keep up with the world. This was primarily due to the lack and poor quality of the components.
AMR — an automated city radiotelephone
The first Czech mobile network called AMR (Automatizovaný Městský Radiotelefon — Automated City Radiotelephone, sometimes also called AMRAD) was started in the mid-1970s in Tesla Pardubice, then a state-of-the-art radiocommunication workplace producing radios and radios. The basis for development was the popular Tesla Selectic radiocommunication system, based on the fact that the station listened to the carrier of its so-called selective choice, which recognized the incoming call. This mechanism of selective choice was also taken to the first Czech mobile network.
A lot later, the AMR network created a number of legends and deposits of half-truths, through which the true nature of this network was somewhat blurred. Therefore, you need to be aware of the starting factors.
Especially in the CSSR at the time of rigid normalization, it was absolutely unthinkable for a normal citizen to use any radio, let alone a cell phone. Even radio amateur licenses and the use of amateur radio stations were under close supervision, unlicensed radio operation was not considered.
The AMR mobile network has been developed strictly for the purpose of postal and telecommunications management, ie for intra-sectoral purposes, especially for network service and in-house roadside communication. This was a prerequisite for the determination of the mobile network as well as the whole solution that had many restrictions for the real “commercial” traffic that the mobile network had attempted twenty years later. Later it was said that its main purpose was to “serve the papalas” — but that was not true, she did not offer enough comfort for this destination and did not really count on it.
Above all, AMR did not expect a participant to be elected automatically, no matter where it is. Since it was intended to be used for state owned telecom company SPT staff always moving within the UTO, it was necessary to select the UTO preference for the call to the AMR network within the reach of the AMR mobile station. Due to the lack of localization of the participant, the development of the AMR system was significantly faster and the system could also be implemented significantly faster. AMR also differed from first generation foreign systems, in fact, it was only analogous to the oldest radiotelephony networks, but it was followed by ten to twenty years later.
Another limitation of AMR was the decision to work with a four-digit numbered space, meaning that there may be a maximum of 10,000 clients in the AMR network.
No other services than the incoming and outgoing calls were expected to be used. No other service has ever been provided. From the outset, it was also not considered that the system should provide foreign telephone connections — employees of the resort did not need it.
Another specialty was the absence of billing support. This made the system very simple and fast to implement. This was later a major obstacle for commercial traffic, with which the operator eventually knew the advice.
Although we are talking about one AMR network, at the time of the greatest glory, there were even three essentially separate AMR networks — experimental, operating on the 162/167 MHz, 161/165 MHz and 152/157 MHz band. These networks were both independent and frequency and if you wanted to switch to another network, you could do this by shifting the channel tuner switch using a screwdriver. User comfort could not be said, the knowledge of the user by whom the branch of the link was assumed was assumed.
The operation of the experimental network began in 1978, the nationwide AMR network was launched in 1983 and the network areas were put into operation in 1987. One year later the operation of the experimental network was terminated.
AMR technology solution
As has been said, the whole system worked on a selective basis, and the individual mobile terminals were basically a radio station equipped with selective selector and keyboard.
The concept of the mobile station was based on the VR21 / 22 radio in a duplex operation at 4.5MHz with narrow band FM Fodulation F3E channel width of 12.5kHz. At the beginning, the duplexer was not used at the beginning, but two separate antennas. At the end of the eighties, the duplex was used, and therefore the only antenna.
When logged into the system, the automaton announced the “UTO” (Area Code) and then united the dial tone. The call was time-limited and was interrupted after the time span, this solution was also used in other analog networks, so it was nothing special. This was because there was no reverse communication with the terminal, and in the event of loss of connection, the base station would not know that the terminal was not in range and still held the assembled connection.
Given that in socialist Czechoslovakia it was almost unthinkable that someone who was not allowed to intercept radio traffic, traffic and AMR were not encrypted and went on an analogue basis. For the same reason, there was totally no authentication of the system participant. Authentication of tune-up networking was only added in 1993, when the release of the country’s political climate and access to radio stations enabled AMR to be used for telephony and when the popular amateur radio amateur was free to call AMR for free.
AMR worked with twelve channels, divided into three so-called four-channel stalks. The radio stations searched channels only within the range of the selected channel, and the service of the mobile station had to switch the stairs by the switch if it came into the area covered by other channels, that is, other stubs.
The AMR base station had an effective range of approximately 15–25 km according to the terrain and at the time of the largest coverage 63 base stations were operating. The base station was connected via a two-wire line to the carriers on the automated telephone exchange.
The principle of the AMR network shows that individual radio stations could communicate directly with each other if they knew their four-digit selective choice and the scapegoat on which they communicated.
Until 1989, AMR was used only for socialist organizations and postal and telecommunication management purposes. Together with the boom in demand for the telephone line after 1989, the attractiveness of AMR has also increased and has been gradually offered to commercial operations. Of course, with a number of compromises that had to be borne in mind that AMR was never intended as a commercially usable network.
However, the commercial operation was not set on roses. First of all, it turned out that the operation of the system is in a legal vacuum, because the license for the operation of the mobile network was acquired in 1991 by Eurotel. The AMR system was therefore operated in part on a “club basis” — it was available to members of a closed club for a flat fee of CZK 1,000 per month (=one third of the monthly income). A member of the club could be anyone who pledged to pay this flat fee. The operator thus dispensed with the unpleasant problem of getting paid for running a system that does not have the ability to charge calls. In particular, it was necessary to rent a radio, there was both a vehicle station and a base station created by remodeling of a vehicle station. Allegedly, manual stations have been developed.
The operation of the AMR system was definitively discontinued in 1999 when it returned to its original use for telecommunications two years before.
The AMR system has thus written a significant part of the Czech chapter of mobile networks, and the reverberation of its fame is still in existence today. Not surprisingly, most of the Czech radio companies have their roots in eastern Bohemia, especially in Pardubice, and many ambitious plans are still coming from this area, whether it’s professional radio network services or, for example, radio security for vehicles and property.