Service manual

Operation GPH Series VHF Radio
Page 3-12 
3.7.6 Busy Channel
If the radio has been programmed for busy channel operation, it will operate in one of the following three
modes:
 Busy Channel Indication
 Busy Channel Lockout
 Busy Channel Lockout Override
3.7.6.1 Busy Channel Indication
The yellow busy channel indicator glows if there is carrier activity on the selected
channel. If the selected channel is a Code Guard channel and the proper Code
Guard value is not detected, the busy channel indicator remains on for the
duration of the carrier activity and no message is heard. During scan and priority
scan operation, the busy channel indicator glows when activity is detected on any
channel on the scan list.
When scanning or priority scanning Code Guard channels with the squelch knob
in the Code Guard position and activity has been detected, the busy channel
indicator glows for the time period necessary to determine if the proper Code
Guard value has been received, causing the busy channel indicator to flash at
various rates.
3.7.6.2 Busy Channel Lockout
The busy channel lockout feature applies only to those channels programmed to
receive Code Guard operation. When carrier activity is detected on the channel
selected, the radio checks the receive Code Guard value. If the proper Code
Guard value is present, the radio can transmit on that channel, even if the
squelch knob is not in the Code Guard position.
If the radio detects an incorrect value or carrier activity only, the transmitter is
disabled, an alert tone is heard, and the display shows the word
BUSY when the
PTT switch is pressed, whether the squelch knob is in or out of the Code Guard
detent.
Channels not programmed to receive Code Guard operation can be used to
transmit regardless of carrier activity.
3.7.6.3 Busy Channel Lockout Override
This mode operates in the same manner as busy channel lockout except that the
user can override and transmit by turning the squelch knob off the Code Guard
detent. The transmitter is locked out only if the squelch knob is set to the Code
Guard detent.
3.7.7 Alphanumeric Display Features
GPH Series portable radios that are built with alphanumeric displays can be programmed with the
following features.
3.7.7.1 Display Backlighting
The GPH radios can be programmed by your dealer to backlight the display when a signal is received or
when a key is pressed. The time duration of the backlighting can also be programmed.