Section 5. Installation
5-2
5.
DISCRIMINATOR
INPUT:
Connect pin 3 to the receiver discriminator
output. Shielded cable must be used for this connection, connect the braid to
pin 2.
Note: If a carrier detect signal from the receiver is not used, then
unfiltered, unsquelched, raw discriminator audio MUST be used for
proper operation of the squelch and receive audio circuits in the
Model 30. Speaker audio may not be used. The discriminator must
pass frequencies above 6 kHz for proper operation!
6.
OPTIONAL CTCSS / DCS DECODE INPUT:
If the Model 30 is
connected to a control station that operates through a community repeater,
or a receiver equipped with CTCSS or DCS decode, the DECODE input
should be used. This will enable the Model 30 to determine the difference
between a busy channel (from co-channel mobiles), and a valid user with
the correct tone. This will prevent co-channel users from accessing or
interfering with the phone patch.
The DECODE input (pin 9) should be connected to the CTCSS or DCS
decoder output in the receiver. The signal must switch between less than 1.5
V
DC
, and 3.5 V
DC
during “decode” and “not-decode” conditions. A jumper
is provided to select the polarity of the signal. If the decode output is low
during decode condition, set jumper JP6 to position “A”. If the decode
output is high during decode condition (or is not required and left
unconnected), set jumper JP6 to position “B”.
7.
COR
INPUT:
If a carrier detect signal is to be provided from the receiver,
connect pin 8 to the carrier active sensor in the receiver. The signal must be
between 0 and 7 V
DC
, and change at least 1 volt between carrier and no-
carrier conditions. The built-in squelch detector can be used if carrier
indication from the receiver is not readily available.
TEST AND ADJUSTMENTS / INITIAL TURN-ON
1.
INITIAL SETTING OF RECEIVE LEVEL AND CARRIER DETECT:
In
order to get started with the rest of the adjustments, it s necessary to do a
rough set-up of the RECEIVE GAIN and the CARRIER DETECTOR
sensitivity. Connect an oscilloscope to U1 pin 14 and set it 0.5 V
AC
/division.
Supply a full quieting signal with a 1 kHz audio tone at 70% of full channel
deviation (typically 3.5 kHz deviation, if a service monitor is not available,
try using a radio with a DTMF keypad, sending any digit continuously will
do). While supplying this signal, adjust the RECEIVE GAIN (R4) for a 1 V
p-
p
signal at U1 pin 14. If you are not able to reach this level with JP1 in the
“A” position, move it to the “B” position.
Once the RECEIVE GAIN is set, remove the signal. Make sure JP7 and JP8
are in the “A” position. Now rotate the CARRIER control counter-clockwise
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