Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Demodulation with variable bitrate?

  1. May 21, 2009 #1
    I am to understand that modems modulate digital signals using techniques such as shift-keying. When a modem receives a signal it demodulates the modulated signal from the telephone line to the original digital signal again.

    Now, the bitrate that is sent/received is often variable. Sometimes the connection is 'slow' or there is line attenuation. In such cases, how does the modem know what the current bitrate is before demodulating? Is there a clock pulse also sent? If the received FSK signal contains a high frequency component for a short duration then does the modem consider it to be '111' or '1111111' or '11111111111111111'? How does it know the bitrate when the modulated signal is continuously the same?
  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted