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Message-ID: <UVYnHQA$mSG5Mwfj@telemetry.demon.co.uk>
Date: Wed, 10 May 2000 10:19:59 +0100
To: rsgb_lf_group@blacksheep.org
From: "Tom Boucher" <tom@telemetry.demon.co.uk>
Subject: Re: LF: RF Ammeters, results, and a new subject
In-reply-to: <002001bfb82d$e6759d50$0a00a8c0@server1.ThreeLakes.ca>
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Larry

Again, at a mobile rally (hamfest) I bought a box of assorted ferrite
and iron dust rings. There were about a hundred, various colours and
sizes all for about a quid! My method of establishing their
characteristics was to take one of each type, wind 30 turns of 30 gauge
and measure the inductance. 

I made up a table of the inductance of each, and this gives me a good
indication as to their suitability for LF, MF, HF or VHF. Inductance
varies with the square of the number of turns so, starting with the 30
turn measured value, it is easy to work out the required turns for a
given inductance. In use, if a core gets hot, I use a bigger one! Not
very scientific but it works.

73, Tom G3OLB


>The Question:
>
>What are the techniques that one might use to take a sample core and
>determine the RF capabilities of the core at different frequencies?  I have
>had some blind luck once finding some red coloured cores that performed
>exactly the same as the expensive ones I bought from Amidon.  A more general
>solution of measurement would be just great - who has some ideas on this?
>
>Larry
>VA3LK
>
>
>
>