ทำไมเครื่องส่ง FM บางเครื่องถึงมีสวิตช์เปิดปิด?

According to your question about the on/off switch for the Fm transmitter,
A long time before, there were such kinds of FM transmitters with on/off switches.
Because, that device also could select the channel (ความถี่), and this device type is connector by connector.
แล้วก็, even if select one channel (ตัวอย่างเช่น, 87.7), he could hear the sound of the external device (by using an FM transmitter).
อย่างไรก็ตาม, if he wants to hear OEM radio except for the 87.7 ช่อง, normally he could hear OEM radio channel 88.5 even if FM transmitter power is on.
แต่, at that time, even though he selected 87.7, another channel also could not hear, ดังนั้น, it needs to power off about Fm transmitter.
After powering off the FM transmitter, he could hear the OEM radio from the OEM speaker.
That’s why needs to add a switch and needs to power on/off if the user wants to use OEM radio.
Our FM transmitter products do not need to add the switch.
Because our FM-16 FM transmitter is a wireless type, the user can adjust the frequency if he also could hear another radio channel during using your FM-16.