5.0 Radio, Speaker and Microphone Requirements
5.1 Radio
5.1.1
Receive Audio
Receive Audio input levels from the radio should be from 200mVp-p to
500mVp-p. The Busy lights activate at approximately 150mV. Receive
audio input levels are normally adjusted using the Volume Controls on the
radios.
CAUTION: When using radios with bridged audio speaker outputs,
connect only one of the speaker output lines to the C250C . Leave the
other speaker output line disconnected and preferably insulated with
shrink tubing. The receive audio return path is via the ground
connection between the radio and the C250C .
5.1.2
Transmit Audio
Transmit audio levels are separately adjustable for each radio and sufficient
gain is available to drive nearly any radio.
5.1.3
PTT
PTT is via an Open-Drain output. This signal pulls the PTT line of the radio
low and will key any radio with a low-true PTT requirement. Maximum
switching capacity of the PTT output is 100V, 1.5A DC.
Some radios use a single line to combine PTT and other control functions.
These radios may not be compatible with the PTT circuitry of the C250C .
Contact NCS for information on use of these radios.
5.2 Speaker
The C250C was designed to drive speakers of 4-8 Ohms nominal impedance. Maximum
power output is achieved with 4 Ohm speakers. Speaker power ratings should be
chosen according to the speaker impedance as shown in this chart:
Speaker
Impedance
(Ohms)
Minimum Power Rating
(Watts-rms)
Selected
4
Ω
4
8
Ω
2
Unselected
4
Ω
4
8
Ω
2
PA
4
Ω
16
8
Ω
8
CAUTION: NEVER ground either side of the PA speaker output
terminals. Doing so may damage the audio amplifier in the C250C .
5.3 Microphone
The adjustable amplifier in the C250C allows most any dynamic or electret microphone
to be used. Typical input level from the microphone should be in the range 50mV-
250mV.
NCS-C250C Instruction Manual Rev J
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