THE MEDHURST FORMULA
The Medhurst formula gives the self-capacity of a coil in picofarads [pF]. It has the following form:
C [pF] = K . D [cm]
where K is the Medhurst coefficient and D, the coil's diameter in centimeters.
K values are a function of the aspect-ratio ar i.e. the height/diameter (H/D) coil.Searching the web and technical books about this topic I've come across the following values, which are shown below. Range of ar is 1 to 10 (common TC secondary values).
Medhursts Original Papers published in Wireless Engineer 1947
- "H.F. Resistance and Self Capacitance of Single-Layer Solenoids" by R. G. Medhurst. Published in Wirelss Engineer, February 1947, pages 35-43.
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- "H.F. Resistance and Self Capacitance of Single-Layer Solenoids - (concluded from page 43 of February issue)" by R. G. Medhurst. Published in Wirelss Engineer, March 1947, pages 80-92.
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