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Velocity Factor and resonant frequency
Reg, G4FGQ wrote:
"I`m even more certain you will find an equation for inductance of an isolated wire of length L: and diameter D somewhere in the bibles." Equation 14 on page 48 of Terman`s 1943 edition of "Radio Engineers` Handbook is: Lo = 0.00508 l (2.303 log 4l/d - 1+mu/4) microhenrys Lo is the (approximate) low-frequency inductance and the dimensions are in inches. Terman also gives the (approximate) low-frequency inductance formula of a single-layer solenoid on page 55 of the same book. One can find the resonant frequency of the coil when using a known capacitance to resonate the coil at a low frequency. Maybe a dip meter could be used. Capacitive and inductive reactances are equal at resonance. Self and stray capacitances are included with the known value of capacitance used to resonate the coil at the low frequency. The resonant frequency is lower than the known capacitance by itself would produce. The resonance formula used with the actual inductance of the coil will give the capacitance of the resonant circuit The difference between the calculated capacitance and the known capacitor value is equal to the stray and self-capacitance total, so it is good to minimise stray capacitance when seeking the self-capacitance value of the coil. An ARRL Single-Layer Coil Winding Calculator is a slide rule which makes things easy. Best regards, Richard Harrison, KB5WZI |