NPX138N Series Panel Mount FM Transceiver
SM41 Installation and Operation Manual
Section 3 Rev: 1.00
Issue 4
Page 3-4
3.6.1
Main RX (Receive) Volume Control
Set this rotary control to the furthest counterclockwise position (past the ‘Off’ detent) to turn ‘off’ the radio.
Rotating it clockwise will turn ‘on’ the radio. To increase the volume of the main receiver, turn this knob
clockwise; to decrease the volume turn this knob counterclockwise.
3.6.2
RX/TX Status Indicator
Next to the main RX volume control is a bi-color LED indicator that displays the RX (Receive) status of
the main receiver and the TX (Transmit) status of the radio. When the radio is transmitting the LED will
light green. When the main receiver receives a signal, the LED will light amber. If the radio is idle (not
receiving or transmitting), the LED will be dark. The color-coding used for these functions corresponds to
standard aircraft FM radio conventions. It is worth noting that this is the reverse of standard vehicular
conventions so may confuse some emergency services staff familiar with land mobile equipment.
The receive indicator (amber) informs the operator that the channel is active with radio traffic of some
kind. A radio that is receiving may still not produce any audio if the tones present on the receive signal do
not match the tones set in the radio. See section 3.11 for further details on how CTCSS tones work.
3.6.3
Scan/Guard TX Switch
When this switch is in the
SCAN
position, the radio will begin scanning. See section 3.12 for further
details on scanning.
When this switch is in the
GD TX
position, all radio transmissions will be on the guard transmit frequency
instead of the transmit frequency of the current channel. The radio continues to receive on both the Guard
and Main receivers. This function only applies to radios with the guard receiver option installed. If not, the
radio will display ‘
GD NOT INSTALLED
’
on the upper line when the switch is set to the
GD TX
position.
Set this switch to the
NORM
position to disable scanning. All radio transmissions will use the transmit
frequency of the current channel.
3.6.4 Guard
Controls
Guard RX Indicator
Guard RX Volume Control
Guard
Select
Switch
The guard controls are functional only in radios with the optional guard receiver installed.
ENG-FORM: 806-0115.DOT
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