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Frequency & wavelength

Everyday concepts such as pressure, flow, altitude, and potential energy are excellent metaphors for DC circuits but can lead to serious misconceptions for AC circuits. The applicability of these everyday concepts becomes worse as the frequency of the AC circuit becomes higher. AC circuit frequencies can be roughly categorized as:

  • line (50-60 Hz),
  • audio (20- 20 kHz),
  • ultrasonic (20 kHz- 500 kHz),
  • rf (500 kHz - 1 GHz),
  • microwave (1-1000 GHz).
A frequency f has a corresponding wavelength l for electromagnetic wave propagation. This wavelength is determined by the propagation velocity c.  The wavelength is l=c/f where c=3x10^8 meters per second in vacuum and 2x10^8 meters per second in a typical cable. A signal with frequency  f =1 MHz thus has wavelength l=300 meters in vacuum and l=200 meters in a cable. Wave propagation issues become critical when the cable length is of the order of  l/4 or longer. In such cases DC circuit concepts fail and transmission line theory has to be used instead.

Troubleshoot ground loops with ease
without disconnecting anything!
US Patent 7,791,353 B2