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NNTP-Posting-Date: Wed, 10 Oct 2012 11:18:13 -0500
Date: Wed, 10 Oct 2012 12:18:03 -0400
From: "Michael A. Terrell" <mike.terr...@earthlink.net>
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Subject: Re: Lighting a LED with ambient RF (was candle)
References: <kmn578h1gkh37evj3ia29h8la253tc23kh@4ax.com> <er8678552j4h10migpv59hfcal5sttaap0@4ax.com> <4i17785u9meh02k1g2cdvkv5bvrcskf9gg@4ax.com> <3aadnekegbJ_q-nNnZ2dnUVZ_tidnZ2d@earthlink.com> <2rg878hj1ktihlvi8j5rtg1gt4dmhhgp8c@4ax.com> <2NednWkZV_nzz-nNnZ2dnUVZ_rqdnZ2d@earthlink.com> <vl3978dofjom28721sbkkml04sa2bkdova@4ax.com> <jPedneeCSssxA-nNnZ2dnUVZ_rOdnZ2d@earthlink.com> <dhc978lq3olanu0vkng970klqemtpugpbh@4ax.com> <gIudnakJAc_G7-jNnZ2dnUVZ_hqdnZ2d@earthlink.com> <5v0b781vqhdddvhn9ckgkssohbq7lim3mb@4ax.com>
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John Larkin wrote:
> 
> On Wed, 10 Oct 2012 09:04:17 -0400, "Michael A. Terrell"
> <mike.terr...@earthlink.net> wrote:
> 
> >
> >John Larkin wrote:
> >>
> >> On Tue, 09 Oct 2012 18:01:06 -0400, "Michael A. Terrell"
> >> <mike.terr...@earthlink.net> wrote:
> >>
> >> >
> >> >John Larkin wrote:
> >> >>
> >> >> On Tue, 09 Oct 2012 12:35:49 -0400, "Michael A. Terrell"
> >> >> <mike.terr...@earthlink.net> wrote:
> >> >>
> >> >> >
> >> >> >John Larkin wrote:
> >> >> >>
> >> >> >> On Tue, 09 Oct 2012 10:38:17 -0400, "Michael A. Terrell"
> >> >> >> <mike.terr...@earthlink.net> wrote:
> >> >> >>
> >> >> >> >
> >> >> >> >John Larkin wrote:
> >> >> >> >>
> >> >> >> >> Why not put the LED right across the crystal set LC tank? The tank
> >> >> >> >> needs capacitance anyhow. We have some high-efficiency LEDs in the low
> >> >> >> >> 10s of pF. The classic crystal set cap was a 365 pF variable.
> >> >> >> >
> >> >> >> >
> >> >> >> >   That would reduce the 'Q' to an unusable level since a parallel L/C
> >> >> >> >circuit is high impedance.
> >> >> >>
> >> >> >> The Q would be reduced in proportion to how much power is extracted by
> >> >> >> the LED. Delivering power into the LED is the whole point, so
> >> >> >> naturally that will reduce Q.
> >> >> >>
> >> >> >> Of course, the impedance match should be optimized for maximum power
> >> >> >> transfer. Crystal sets often used tapped inductors for that reason, so
> >> >> >> thet might be reasonable here.
> >> >> >
> >> >> >
> >> >> >   And the voltage would be lower at that tap.
> >> >>
> >> >> Depends on what you connect to which tap.
> >> >
> >> >
> >> >   Have you ever seen a _working_ crystal radio with the capacitor
> >> >connected to the tap?
> >>
> >> No, but we're making a night light, not a crystal radio. And I didn't
> >> say that the cap had to be connected to the tap, but it might make
> >> sense.
> >
> >
> >   Then build it, and show us.
> 
> Not this month; I have a day job. The big hassle would be stringing up
> the antenna.
> 
> There's little doubt, from the math, that it would work, at least
> enough to get some visible light out.


   Cat whiskers & Germanium diodes have a very low forward drop.