Date: Fri, 22 Oct 2010 10:09:25 -0700 From: David Brodbeck <gull@gull.us> To: freebsd-questions@freebsd.org Subject: Re: Greybeards (Re: Netbooks & BSD) Message-ID: <AANLkTin9X3%2BXg4D-B5CyM2CcQDQrDMC5Ja-KnhxOjYZe@mail.gmail.com> In-Reply-To: <4CC040E7.7090404@qeng-ho.org> References: <op.vj5o9ixxhtl4zj@ack5833s2.ad.service.osu.edu> <20101017143901.GA71132@current.Sisis.de> <alpine.BSF.2.00.1010171215030.96626@wonkity.com> <20101019074615.GA2183@current.Sisis.de> <alpine.BSF.2.00.1010191448390.6689@wonkity.com> <20101020022946.GA23035@thought.org> <20101020052601.GA1977@current.Sisis.de> <4cbe9e9a.3qT7q8JUqJxSD8/V%perryh@pluto.rain.com> <20101020165526.GA25310@thought.org> <4CBF21EB.1080003@tundraware.com> <20101020194605.GA78565@stainmore> <4CBF4CB4.6070902@qeng-ho.org> <20101021133844.235fdc72@gumby.homeunix.com> <4CC040E7.7090404@qeng-ho.org>
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On Thu, Oct 21, 2010 at 6:32 AM, Arthur Chance <freebsd@qeng-ho.org> wrote: > Dredging up physics unused for 30+ years, ferrite is ferromagnetic and > intensifies magnetic fields so a coil of wire with ferrite inside is a > massively bigger inductor then an empty coil. I vaguely remember that brass > is slightly diamagnetic, but could be mistaken. Bingo. A ferrite slug increases the inductance of a coil, relative to an air core; a brass slug decreases it. I've got a homebrew amateur radio transceiver that uses a coil with a brass machine screw in it for tuning. Wind the screw out of the coil, inductance goes up. A cheap and simple form of permeability-tuned oscillator.
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