If a digital signal is mis-tuned, the TNC will not be able to copy the message. Answers to the following questions can help us learn to tune our radios for best reception. The TNC expects to receive the same tones it transmits. A TNC usually has a bargraph of LEDs that light in a certain manner when the signal is properly tuned. While this accomplishes the task, additional information may help us eliminate the noise that is also received with a normal SSB signal.
Digital information is sent as a signal that changes between two tones.
If we do the math, the difference between 2125 and 2295 is 170 Hz. The difference between 1275 and 1445 is also 170 Hz. Therefore, a signal sent with tones of 1275 and 1445 can be received as tones at 2125 and 2295 and carry the same digital information. You do not need to be concerned with which tones another station transmits to you. When a radio receives a signal in its passband, the radio produces tones that you hear from the radio's speaker.