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- To: tesla-at-pupman-dot-com
- Subject: Calculation of Q?
- From: Steve Falco <sfalco-at-worldnet.att-dot-net>
- Date: Sat, 08 Mar 1997 15:53:45 -0500
- Sender: falco-at-poodle.pupman-dot-com
I came across an equation for calculating the Q of a solonoid coil in the ITT book "Reference Data for Radio Engineers". The formula is: Q = A * d * sqrt(f) where A is a coefficient that varies with the ratio of Length/Diameter, d is the diameter in inches, and sqrt(f) is the square-root of the frequency in megahertz. Some approximate values for A: A=102 when L/D=1 A=120 when L/D=2 A=130 when L/D=3 A=135 when L/D=4 A=137 when L/D=5 I tried using this formula with a number of different theoretical coils. In each case, I calculated a Q value which was about 2.7 times higher than that obtained from the TESLAC program. I don't know if TESLAC derates the Q by a fixed factor to account for empirical losses, or if the difference is due to something else. The ITT book does state that the above formula is only good when the thickness of the wire is > 2.5 times the skin depth of the current. Also, the formula assumes the winding density is between 40% and 80%. I believe typical secondaries are more nearly at about 95% winding density (i.e. closewound). Perhaps these items account for the difference. Does anyone have a (reliable :-) formula for the Q of a solonoid given the typical dimensions and winding density of a Tesla coil secondary? Steve Falco sfalco-at-worldnet.att-dot-net
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