Retevis RT638 Operating Instructions Manual page 5

Your unit is an open-license band. Always identify yourself when transmitting on the same channel.
IMPORTANT: Before transmitting on a channel listen to ensure it is not already in use.
CTCSS/DCS
Press the Menu/PWR button twice and use the Up/ Down to introduce
CTCSS/DCS Continuous Tone-Coded Squelch System or CTCSS is a circuit that is used to reduce the
annoyance of listening to other users on a shared two-way radio communications channel. It basically allows a
private CH on a busy stream.
CTCSS = Coded tone controlled squelching system. This allows you to talk on a private sub channel on an active
channel.
DCS is a digital extension of CTCSS.
DCS=DCS is a digital extension of CTCSS. It provides extra, digitally coded, squelch codes that follow after the
38 CTCSS codes. CTCSS 1 to 38 ,followed by DCS 1- 83.
VOX
Voice operated transmitter, it allows you to transmit with your voice without pressing the button.
Your communicator is equipped with an adjustable Voice Operated Transmitter(VOX) that can be used for
automatic voice transmission.
In this convenient mode,transmission is automatically initiated by speaking into the microphone.There is no need
to push the button.
By press Menu/PWR button 3 times,screen will display VOX character,character OFF keep flashing. Press Up or
Down button to select voice level(from 1 to 3 level or OFF), by pressing PTT button to confirm setting. VOX
default setting is off.
CA
Call allows you to adjust different tones for calling the operator from the same channel.
Press Menu/PWR button 4 times, screen will display CA character, digital 01 keep flashing, by pressing UP or
Down button to select call tone from01~10, then press PTT button to confirm call tone setting. Default setting for
call tone is 01.
There are 10 mode call tones in this unit. You and other party can use designed call tone to communicate
separately, secretly to avoid any disturb.To activate this feature, when the unit in normal mode, press twice
quickly and release the PTT button to send a tone to other users on the same channel.
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