From: Paul
Date: Mon, 18 Dec 2000 19:20:58 +0000
Subject: [TSSP] Proximity effect and Terman
In a recent thread on the main tesla list concerning base input impedance, Bert Hickman commented: (Referring to Terman's "Radio Engineers Handbook, McGraw-Hill, 1943.) > ... > Terman's proximity effect analysis assumes lumped behavior - that > the same current flows through all portions of the resonator. We also > know that the resonator base current is ultimately balanced by the > displacement currents "flowing" through the distributed capacitances > of the resonator and topload - and that these currents are not the > same in all portions of the resonator. This makes Terman's approach > of estimating proximity effect of limited use in base-driven > resonators. We are fortunate that Bert recently joined this project list. Bert, Welcome to the tssp list! From reading your comments in the tesla list, it sounds like you might be able to shed some light on what is for a me a mystery - the origin of the proximity effect and how to estimate it. I'm not familiar with Terman's tome, so maybe you could advise whether the analysis given there for the case of uniform current could be made to apply to the non-uniform case, given that we can now calculate the current distribution of the secondary with reasonable confidence? Any comments you can make which might help me understand the mechanism involved in the proximity effect would be most appreciated. While I have several books which go into skin effect, none do more than mention the existence of proximity effects in closewound inductors. At present, the tssp simulator makes use of Medhurst's tables to estimate the effective series resistance, and the resulting input impedances and Q factors compare poorly with measurement, often being 50% in error, sometimes more. It would be very nice to find a more reliable approximation. Cheers, -- Paul Nicholson, Manchester, UK. --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.