You can open and use the radio manually through the M / F1 Menu
Go to:
M / F1 Menu > Roleplay Options > Open Radio
This opens the radio interface.
Use the radio controls to enter the frequency you want to join.
Type the radio frequency number into the radio and connect to it.
This lets you manually join the required radio channel rather than using the quick emergency RTO selector.
You can also adjust the radio volume from the radio interface.
Use the available volume controls to make radio traffic louder or quieter depending on your preference.
From the radio interface, use the button in the top-right to open the RTO / Radio Operations screen.
From there, you can view available RTO channels and connected units.
1. Open M / F1 Menu
2. Go to Roleplay Options > Open Radio
3. Type in the radio frequency number you want to join
4. Connect to the frequency
5. Adjust the radio volume if required
6. Use the button in the top-right if you want to open the RTO / Radio Operations screen