1. How to select the radio area?

For S series following: Car Settings-General-Radio area selection. 
For HC series following: Settings-Car Settings-Radio Region.

2. How to change the searching interval for radio frequency?

For S series following: Car Settings-General-Radio area selection. 
For HC series following: Settings-Car Settings-Radio Region.

3. How to make radio function working when using navigation?

For S series following: Car Settings-Navigation-Navi remix- on.

For HC series following: Settings-Car Settings-Sound-Media volume when navi-on.

4. Why the radio signal is weak? 

A. Must select the correct radio area for your local, so that it have good signal.
B. In some car models, the original radio antenna is active, this original radio antenna have two FAKRA adaptors, look at the below picture.
In this case, buyer need to buy an additional two plug radio antenna, see the below picture.

Using this active radio antenna, you need to get power from G8 pin (ANT blue wire) on player power cable set.

5. How to turn on / turn off RDS?

For S series following: Car Settings-General- Radio RDS switch-ON/OFF
For HC series following: Settings-Car Settings-Factory-000000 ok- RDS-ON/OFF