WHILE YOU may be tapping your foot to
music on the All India Radio's I'm
(Frequency Modulation) channel, the
same broadcast band (87.5 - 108 MHz)
may also be serving to contact a
doctor required to attend to an
emergency call. The I'm Radio Data
System (RDS) - a paging service - is on
Paging is a one-way transfer of precoded messages to persons concerned
only, explains P S Sundaram, director
(engineering), R&D, AIR and Doordarshan. The RDS paging system was introduced early this year.
To page a subscriber, a phone call to
the paging service control room does
the trick. The operator types the message into a computer, which is transmitted to the encoder - a device which
receives the message in the binary code
and transmits the same to the Very High
Frequency FM transmitters. This binary
code is radiated from the transmitter as
a sub-carrier in the I'm broadcast band.
But its frequency (57 Kilohertz) does
not fall in the audible range for the
human ear, and so does not interfere
with the FM music channel broadcasts,
explains S K Rajagopalan, assistant
research engineer with AIR.
Each pager has an individual number or address called Cap code preprogrammed into it. The Cap code helps
the pager to scan through the different
radio frequencies and lock to the right
The RDs does not require exclusive
frequencies - it uses the idle capacity of
the FM channel, which can transmit
1187.5 bits per second - and this, in
turn, reduces the infrastructural costs,
thus giving a low cost nationwide paging service. Registration for radio paging costs Rs 1,000 and monthly service
charges vary with the type of pager used.
The @adio paging allows coverage of
a 60 kin radius. Intercity paging is done
via the control room operators who call
their counterparts in the city where the
service is available and the message is
delivered to the particular pager number.
With 85 FM stations already in existence and another 140 on the anvil, the
AIR appears determined to succeed in its
plans to link up the country with a fast
and efficient communication mode
before the turn of the century.