4-36 Technical Description 8525B/8528 Technical Service Manual
Issue 6 Publication No: 15-02036
Figure 4.1 Selective Call Scanning
4.13.3 RTTY—ARQ Mode
With Option PS fitted the transceiver can be used for ARQ mode teletype
transmission and reception. The teletype interfacing equipment is connected
to J301 in the same way as the selective calling equipment. Refer to the
table in section 1.2.4 for the pin connections and the levels acceptable for
each function. Note that Option PS cannot be fitted if any of the internally
fitted selective calling function are fitted.
Note: It is essential to use J301 for the PTT connection in this mode. The
switching time of the PTT function at the microphone connecter on
the front panel is unacceptably long for ARQ operation. (The
transmit/receive switching time at J301 is 20ms).
If scanning is used in this mode (depending upon the external equipment
used), it may be necessary to enter the same channel into consecutive
positions in the scan program in order to dwell on each channel long enough
(in the order of 2 seconds) for the detection of RTTY - ARQ mode signals.
This will, of course, restrict the number of channels that can be scanned.
Scanning must be carried out in the Quiet Line mode, i.e. with +10V applied
to the Quiet Line input. The Alarm Tones input must be taken low (0V) by
the external equipment to stop the scanning.
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