Carrier-Operated-Switch; Push-To-Talk - ACC RC-85 Owner's Manual

RC-85 Repeater Controller Owner's Manual

Carrier-Operated-Switch

The output from the receiver which indicates that a signal is present is called
COS, or carrier-operated-switch. It's a logic signal which is at a particular logic
state when a signal is at the receiver's input, or the squelch is open, and at the
opposite state when the squelch is closed. Most receivers designed for repeater
service have such a logic output, called "COS", "COR", "squelch gate", or
something similar. With other receivers, such as transceivers put into repeater
service, it's necessary to find a usable logic signal for COS. Look after the FM
detector, following the noise amplifier and rectifier in the squelch circuit, for a
usable signal. Contact the factory if you need help with your particular receiver.
Since signals from different receivers can vary in characteristics, the RC-85
controller is designed to accept a variety of logic levels and to accept "high true"
and "low true" signals. The only requirements are that a logic low be less than
.8 volts and a logic high be greater than 2.4 volts (up to about 15 volts). The
COS input impedance is approximately 10K ohms so that it won't load down the
circuitry providing the COS signal. A DIP switch on the controller board allows
selection of high or low true, based on what your receiver provides (see "Setting
DIP Switch Options" later in this chapter).

Push-to-Talk

The PTT (push-to-talk) signal is just as easy to interface to the transmitter. The
controller provides a solid-state switch closure to ground capable of sinking up to
about 100mA from a positive source. Most any transmitter has a keying line
(PTT), so if a contact closure to ground normally keys the transmitter, you're in
business. If a logic high keys your transmitter, the controller board also allows
PTT high true operation, so that a pullup resistor on the output can define a
logic one level to the keying logic. High or low true operation is selected by a
DIP switch option (see "Setting DIP Switch Options" later in this chapter).
If your transmitter has negative voltage on the keying line, it's necessary to
buffer PTT with a relay or other transistor circuitry. The PTT transistor switch
is capable of keying positive voltages only and may be damaged if connected to a
negative voltage. If greater than 100 mA is required for keying the transmitter,
the PTT output can be buffered with a larger transistor or relay.
(Installing in Your Repeater) 2 - 2 V3 4/87