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Questions about frequency and pattern

  1. Feb 14, 2012 #1
    I keep getting differing definitions of high frequency. I've seen that it means frequencies from 3 to 30 MHZ. Also I have seen one that claims that it is more around 500 MHZ. Also, is their such a thing as a high frequency square wave signal?
     
  2. jcsd
  3. Feb 14, 2012 #2
    High frequency is a relative term that depends on the context you see it used in. Are we talking about computer signal frequencies, radio communication frequencies, audio range, or seismic earth wave frequency? They will all have different frequencies that are considered "high frequency" for their purpose.

    Mathematically, a square wave can have any frequency. There are lots of square wave signals used in the real world that can be considered high frequency, although there are limits based on which technology is used and the other properties of the signal.
     
  4. Feb 14, 2012 #3
    There are all different definitions. Yes, you can have high frequency square wave, getting a 500MHz is not that hard. You can have rise time under 100pS, for a 2nS square wave of 100pS transition time is pretty square wave to me. But at higher rate like in over 1GHz, it is not really as square because your measuring instrument has limit also, you don't exactly see a perfect square wave.

    Yes, more of the serial communication are using pulses like square wave. Firewire and USB being two example of 400MHz data rate.
     
    Last edited: Feb 14, 2012
  5. Feb 14, 2012 #4
    A high frequency AC electrical signal.
     
  6. Feb 14, 2012 #5
    The different bands in the EM spectrum have names, where 3Mhz to 30MHz is arbitrarily called the HF band. But it seems to me that you're asking what is considered high frequency in electronics in general, which to me is like asking what is high speed in a mechanical system (15km/h is fast enough according to my grandma).

    The only useful notion of "high-speed" in electronics that I know of, is a system whose signal wavelength (divided by 10, as a rule-of-thumb) is shorter than the system's physical length.

    Small systems have a low self-resonant wavelength, and vice versa, so in many ways a 50Hz (λ/10 = 600km) signal on a power-line from NYC to LA (distance = 4000km) is as high-speed as a 2Ghz signal on a 10cm wide PCB.
     
    Last edited: Feb 14, 2012
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