Codan Radio MT-3 - Manual (Page 20)

USER GUIDE | MT-3 ANALOG RADIO SYSTEMS
Chapter 2: Technical Information Page 12
Squelch Settings
The receiver squelch settings can be jumper selected for one of two different squelch detection methods.
The standard squelch method is a noise operated squelch, while the optional squelch method is based
on carrier level (RSSI). The squelch point can be set (using either method) by a variable resistor in
the receiver module. A second variable resistor is used to set the hysteresis between the squelch and
unsquelch points. A receiver mute line attached to the squelch circuitry can squelch the receiver when
active (typically used in CTCSS systems). A squelch override signal line can be used to unsquelch the
receiver.
External Connections
External audio and control (PTT/COR) signals are typically connected to a Codan radio system through
the AC-3E Audio Control Card (the AC-3L-96, AC-3M-96 and AC-3S-96 Audio Control Cards have
no external connections available). The AC-3E Audio Control Card contains four 600 ohm balanced
transformers for two auxiliary audio inputs and two auxiliary audio outputs. Control signals (PTT/COR)
to or from external equipment are optically isolated allowing for more fl exibility in external equipment
voltages.
It is recommended that external audio connections are made to the AC-3E Audio Control Card and NOT
to the balanced audio connections on the receiver and transmitter modules.
Audio Level Adjustments
The AC-3E AC-3M-96 and AC-3S-96 Audio Control Cards allow independent level control of all audio
in a Codan radio system (the AC-3L-96 Audio Control Card has no audio level control capability). The
AC-3E Audio Control Card has four audio level control variable resistors on the front panel for receiver
to transmitter level adjustments, and four audio level control variable resistors inside the module for
auxiliary audio level adjustments. The AC-3M-96 and AC-3S-96 Audio Control Cards have six audio
level control variable resistors on the front panel for receiver to transmitter (and slave to master / master
to slave) level adjustments.
The AC-3L-96, AC-3M-96 and AC-3S-96 Audio Control Cards were discontinued in 2006.