Re: Topband: core inductance and current - some measurements.

[Robert Kavanagh <ve3osz@rac.ca>]

At 08:21 PM 11/17/03, N0TT wrote:

> The indicated inductances with just *3-1/3 turns* on the 73 mix Binocular
>
> core were:
>
> 0 ma    90.04 uhy
> 15 ma 90.04 uhy
> 29 ma 89.71 uhy
> 58 ma 97.11 uhy
> 110 ma 75.41 uhy
>
> My remote relays draw around 40ma and there is no
> significant change in inductance with a steady ~40ma current
> through the choke...so for Topband use, those cores, IMHO,
> are perfectly OK to use for chokes for lower-current applications
> like relays.  Looking at the  above readings though, one can see that
> the inductance starts to drop off with currents in the neighborhood
> of 100 ma.

It is not just the current that must be considered.  This effect also 
depends upon the number of turns and the dimensions of the core.  11 mA 
through a 33  turn coil on the same core would have the same effect as 110 
mA in a 3-1/3 turn coil.

See the hysteresis curve for 73 mix in the Fair-Rite catalog for more 
information. Also see page 56 in QEX for May/June 2003 for an example of 
how the inductance of a coil wound on type 43 material changes when d.c. 
flows in a winding.

Bob, VE3OSZ 

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