Re: Ferrite types and choke formulae (?)

To: "'Tesla List'" <tesla-at-poodle.pupman-dot-com>
Subject: Re: Ferrite types and choke formulae (?)
From: Tesla List <tesla-at-stic-dot-net>
Date: Sat, 15 Nov 1997 23:27:00 -0600
Approved: tesla-at-stic-dot-net

From: 	Adam[SMTP:absmith-at-tiac-dot-net]
Sent: 	Saturday, November 15, 1997 11:02 AM
To: 	tesla list
Subject: 	Ferrite types and choke formulae (?)

Does the Wheeler formula work only for air core solenoids, or can I use 
this also for coils wound on a ferrite rod, just by multiplying by the 
appropriate permeability?

INDUCTANCES:

I am looking for a practical formula for choke inductances.  I have an EE 
degree, and I have plenty of electromag texts, but I am finding that the 
purely mathematical formulas for inductance of a fixed length solenoid 
(via. Biot-Savart law) gives results that are so far from the actual 
measured values of the inductors produced, that the calculation is 
essentially useless.  (It's too ideal). On the other hand, the formula 
for the ideal capactior (K*A/d) is very accurate; real world caps are 
quite close to the ideal calculated value when pure and uniform materials 
are used.

FERRITES:

Also, does anyone know the difference between the different types/grades 
of ferrites?   I am most interest in the frequency ranges and 
*permeability* values.  Does the tesla list have a nice table for this, 
as it does for dielectric constants?  My surplus catalogs have ferrites 
listed as materials HF-70, 43, 61, 70, 73, 77, white mix, and orange mix. 
 They all seem to indicate that 43 and 43 Mixes are the most widely 
applicable, good up to 200MHz.  What type is found in TV Flyback cores 
(that's what I am using now for my RFCs).

-Adam

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Epoch, Inc. Digital Music Project

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