Icom IC-251A Instruction Manual page 14

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FUNCTION
Output from squelch control stage. (+7V when squelch is ON)
13.8 Volts DC in conjunction with the power switch operation.
(0.3A Max.)
Connected to Push-to-talk, T/R change-over switch. When grounded, the
set operates in the transmit mode.
Output from the receiver detector stage. Fixed output regardless of AF
output of AF GAIN Control.
Output from Transmitter MIC amplifier stage.
8 Volts DC available when transmitting. (Relay can not be directly
actuated. 5mA Max.)
Input for external ALC voltage.
Ground.
NC (no connection).
Control signal (DBC) input terminal for external control.
NC (no connection).
NC (no connection).
Control signal (DV) output terminal for external control.
Control signal (RT) input terminal for external control.
Data signal (DB1) input/output terminal for external control.
Data signal (DB2) input/output terminal for external control.
Data signal (DB4) input/output terminal for external control.
Data signal (DB8) input/output terminal for external control.
DC POWER SOCKET
Connect the included DC power cable when DC operation is required. Connect the included
jumper plug to this socket when AC operation is required.
EXTERNAL SPEAKER JACK
When an external speaker is used, connect it to this jack. Use a speaker with an impedance of
8 ohms. When the external speaker is connected, the built-in speaker does not function.
SCOPE TERMINAL
This terminal brings out the 10.7MHz IF signal from the mixer in the receiver. Observation
of not only the received signal, but also of signals of the selected band width are possible by
using a panadaptor or panascope.
SPARE TERMINAL
This terminal is available for your personal use, such as for adding accessory circuits, etc., if
desired.
ANT (ANTENNA) CONNECTOR
This is used to connect the antenna to the set. Its impedance is 50 ohms and connects with
a PL 259 connector.
MEMORY SWITCH
When this switch is in the ON (up) position, the power to the CPU of the IC-251A/E is
supplied continuously, even when the POWER Switch on the front panel is turned OFF, to
retain all the programmed frequencies in the Memory Channels, the operating frequencies of