Message-ID: <000a01c4e9bb$94d59d00$45e4fc3e@l8p8y6>
From: "hamilton mal" <g3kev.ham@virgin.net>
To: rsgb_lf_group@blacksheep.org
References: <000001c4e9a8$996d9650$e6a4c593@RD40002>
Date: Fri, 24 Dec 2004 12:49:38 -0000
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Subject: LF: Re: RE: Re: RE: M0BMU mods for G0MRF 300 W Tx
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----- Original Message -----
From: "james moritz" <j.r.moritz@herts.ac.uk>
To: <rsgb_lf_group@blacksheep.org>
Sent: Friday, December 24, 2004 11:06 AM
Subject: LF: RE: Re: RE: M0BMU mods for G0MRF 300 W Tx


Dear Mal, LF Group,

I mean a deliberately introduced gap as used to provide a higher energy
storage capability in a line output transformer. The gap is usually of the
order of 0.5 - 1mm, produced either by having plastic film spacers between
the core haves, or by machining the legs of the core to unequal lengths. If
you want to use the core for a straightforward transformer, the air gap is
not wanted - no problem to remove the spacers, but difficult when the core
has been machined. Provided the mating surfaces of the core halves fit
together accurately when they are clamped, the core will behave like a solid
lump of ferrite, but quite a small fraction of a mm gap will change the
inductance radically, since the permeability of the gap is much lower than
that of the ferrite. Usually, the mating surfaces of the ferrite are
accurately ground flat by the manufacturers to ensure a good fit.

Tnx Jim for the clarification. My type has nice flat machined surfaces that
fit nicely together when the plastic spacer is removed. Both halves of the
core are symetrical and some are marked 3c8. I tried one of these in the
G3YXM design with the same number of turns as he specified for his type of
core and did not notice any difference in matching or output etc. The
advantage being that they cost me NOTHING hi. They came out of the older all
tube type TV'S of yesteryears hi. I have held on to them for years and now
find them useful.
73 and Merry Xmas and HNY to you and all the LF fraternity including the
silent LISTENERS IN and those sitting on the FENCE.

Mal/G3KEV/Scarborough/England


Cheers, Jim Moritz
73 de M0BMU

Hi All
I have used these cores and noticed no difference between them and a
continuous type core. I put the two core halves together tightly and used
the same number of turns as used on the continuous core, maybe I was lucky.
What does Jim call a gap? If they are tight together is that considered a
gap? Must the core be totally continuous?
de Mal/G3KEV