Spark Transmitter

Design Rules

This seems to work, theoretically anyway:
  1. Determine the operating frequency - your choice here.
  2. Characterize the antenna impedance at the operating frequency. See Characterizing the Antenna.
  3. Calculate and select the storage capacitor as follows:

    Cs = 1/2πF√R

    Cs is the storage capacitor value in farads,
    F is the operating frequency in Hz, and
    R is the resistive component of the antenna impedance in ohms.

    Select (or build) a storage capacitor with a DC voltage rating twice the output voltage of the transmitter power supply. This capacitor must be a low-dissipation ceramic or glass plate type.

  4. Calculate and build the resonating inductor as follows:

    L = √R/2πF

    L is the resonating inductor value in henries,
    R is the resistive component of the antenna impedance in ohms, and
    F is the operating frequency in Hz.

    Construct a single-layer resonating coil using the following design formula:

    L(µH) = (d2n2)/(18d + 40λ)

    L(µH) is the value of the resonating inductor in micro henries (henries x1000000),
    n is number of turns,
    d is the diameter of the coil in inches and
    λ is the length of the coil in inches (inches = cm x .3937).

    Note: The equation loses its ability to accurately predict coil inductance if the turns are widely spaced.

    Or use this CALCULATOR.

  5. Select the output coupling device (capacitor, inductor or direct connection).

    1. If the reactive component of the antenna impedance is zero (ie, the antenna is resonant at the desired operating frequency) the coupling device will be a direct connection - no capacitor, no inductor, static discharge resistor not needed.

    2. If the reactive component of the antenna impedance is positive (ie, inductive), the coupling device will be a capacitor. Calculate as follows:

      Cc = 1/2πFXL

      Cc is the value of the coupling capacitor in farads,
      F is the operating frequency in Hz, and
      XL is the reactive component of the antenna impedance in ohms.


    3. If the reactive component of the antenna impedance is negative (ie, capacitive), the coupling device will be an inductor. Calculate as follows:

      L = Xc/2πF

      L is the value of the coupling inductor in henries,
      Xc is the reactive component of the antenna impedance in ohms, and
      F is the operating frequency in Hz.

      Construct a single-layer coupling coil using the following design formula:

      L(µH) = (d2n2)/(18d + 40λ)

      L(µH) is the value of the coupling inductor in micro henries (henries x1000000),
      n is number of turns,
      d is the diameter of the coil in inches and
      λ is the length of the coil in inches (inches = cm x .3937).

      Or use this CALCULATOR.

      Static discharge resistor not needed.

      CLOSE


    Related Pages

    Characterizing the Antenna

    Constructing an Impedance Bridge

    Spark Transmitter


       
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