Spark Transmitter
Design Rules
This seems to work, theoretically anyway:
- Determine the operating frequency - your choice here.
- Characterize the antenna impedance at the operating frequency. See Characterizing the Antenna.
- Calculate and select the storage capacitor as follows:
C_{s} = 1/2πF√R
C_{s} 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.
- 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) = (d^{2}n^{2})/(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.
- Select the output coupling device (capacitor, inductor or direct connection).
- 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.
- If the reactive component of the antenna impedance is positive (ie, inductive), the coupling device will be a capacitor. Calculate as follows:
C_{c} = 1/2πFX_{L}
C_{c} is the value of the coupling capacitor in farads,
F is the operating frequency in Hz, and
X_{L} is the reactive component of the antenna impedance in ohms.
- If the reactive component of the antenna impedance is negative (ie, capacitive), the coupling device will be an inductor.
Calculate as follows:
L = X_{c}/2πF
L is the value of the coupling inductor in henries,
X_{c} 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) = (d^{2}n^{2})/(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.
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