SECTION б - INSTALLATION
TRANSMISSION ADJUSTMENTS
The digital transmitter broadcasts an FM carrier modulated by the digital
paging waveform that the Paging Terminal provides. The paging waveform
represents a long string of bits, logical ones and zeros, and the
transmitter converts each bit to a nominal frequency shift of plus or minus
4.5 kHz. The Model 16 supplies an RS-232 level signal on J2-9 for this
purpose.
There are 3 tests available in the Programming mode designed to help with
the transmitter adjustments. Any of these tests can be performed with a
serially connected or a modem remoted CRT.
Adjusting the digital FM deviation:
1.
Monitor the radio channel with a deviation meter or oscilloscope and
find the adjustment on the transmitter for changing the deviation
level. Select the "Digital preamble" test by typing "D". Enter a bit
rate of 600 (a typical paging rate) and type CR. This will key the
transmitter and broadcast a 300-Hz digital square wave. Adjust the
transmitter to obtain a peak deviation of 3 kHz to 5 kHz. Type CR when
finished to end the test and unkey the transmitter.
If this adjustment is easily obtained proceed to step 3. If there is
a problem getting the desired deviation, continue with step 2. Type
CR when
to end testing.
2.
Another test will produce a sustained logic one or zero level at the
digital output. Select the "Digital level" test by typing "L". Type
"P" and make the adjustment to the desired deviation, then type CR,
repeat the test and type "N" to check the adjustment for the opposite
frequency shift. Both shifts should be of the same magnitude.
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