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NHRC-2 User Guide
NHRC-2 User Guide
Page 3
2/28/2000
Copyright © 2000, NHRC LLC
All Rights Reserved.
Electrical Connections
Pin
Use
1
Ground
2
+13.8 Volts
3
PTT (active low)
4
TX Audio
5
RX Audio
6
CAS +
7
CAS -
8
Ground/TX Audio Return
9
Ground/RX Audio Return
Receiver audio can typically be taken from the high side of the squelch control.
This audio must be de-emphasized with the controller's optional de-emphasis
circuit, which provides a -6dB/octave slope. Optionally, audio can be taken from
later in the receiver's audio chain, where it is already de-emphasized. Care must
be taken that this source of audio is not subject to adjustment by the radio's
volume control. If the receiver audio has not been properly de-emphasized, either
in the receiver itself or on the controller board, the repeater will have a very
"tinny", unnatural sound to it.
To de-emphasize the receiver audio on the controller board, install a 0.0068uF
capacitor in position C3, change R3 to 51K, and change R4 to 510K. These
values should be considered a good starting point. You may want to experiment
with the values of C3 and R4 to get better sounding audio. We have had
consistently good results with this de-emphasis network.
The receiver must provide a signal present indication (also called COR, RUS,
CAS) to the controller. Because of the varieties of polarity and state that this
signal can take, we have chosen to implement the controller's signal present input
with an opto-isolator (ISO1). The anode and cathode of the LED in the opto-
isolator are exposed through a current limiting resistor (R30). This allows easy
interfacing to active-high, active-low, and combinations of both to indicate the
presence of a received signal to the controller. Clever wiring can allow the user to
create CTCSS and COR, CTCSS or COR, etc. configurations. Note that both the