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| Fig. 299 - One of the first mobile radio
telephony system used for police application purpose. |
For historical allocation purpose the concept of mobile radiotelephony
started before the turn of XX century when Thomaz Alva Edison
demonstrated by the first time a system which permitted telegraphic
communciation between a moving train and a base station, without
requiring physical connections. As aforementioned in the Edison’s
system it was used telegraphic signals only. Therefore, it
was not until two decades later the first mobile radiotelephony
systems were adopted for transmitting messages from fixed
points to moving vehicles. Police department were among the
first to use this means of communication.
Messages were transmitted by radio frequencies just above the
AM broadcast bands that were picked up by receivers in the patrol
cars. Since the vehicles were not equipped with transmitters,
patrols car crews’ had to reply by land telephone, generally
fixed in strategic points in the city. Fig 299
Radio amateurs contributed greatly to the
 |
| Fig 299A -Mobile radio
telephony system used by the British police circa 1960. |
improvement of mobile radio as based in their considerable experience
operating in 5 and 10-meter band the same was extended to the
developement of the first mobile transmitters in the 30 and
40 MHz. In the early system the transmitter operates in
amplitude modulation while some sets used superregenerative
receivers. But, crystal-controlled superhetorodyne units soon
outmoded these types of equipments.
Shrotly after WWII the manufacturers launched in the market
frequency modulation Mobile radio equipment.
The mobile radio equipment had many applications either for
military as well as civilian purposes arisen several types
of services which specific frequency allocations. Among them
the citzen band, in the 11 meter band or 27 Mhz that facilitate
so much two way mobile communication for business of pleasure
by operators without any technical knowledge such as physicians,
engineers, taxi drivers, farmers and so forth. Fig. 300
As aforementioned amateur radio played a very important part
through all the years of the development of radio. The knights
of the ether stand as contributors to progress alongside the
technical giants, the great industrial laboratories, government
projects and university researches in such way the radio receiver
became a popular instrument.
| Fig. 300 - Several types
of radio receiver used for citzen band application. |
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| Fig. 300 - 14 channels transceiver
model BB-12 made by Hallicrafters Company in the USA. |
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Móbile citzen band three channels
transceiver made by Midland in the USA. |
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