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Re: 1/4 Wave, etc.
From: Greg Leyh[SMTP:lod-at-pacbell-dot-net]
Sent: Saturday, September 13, 1997 4:58 AM
To: Tesla List
Subject: Re: FW: 1/4 Wave, etc.
Dan Kline wrote:
> >[GL wrote]
> >It does not seem that the sec wire length makes an appreciable
> >difference in the performance of a standard TC.
> >
> >I have noticed in PSPICE that typical TC secondaries with even moderate
> >top loads do not exhibit any significant standing wave behavior, but
> >operate more as simple LC resonant circuits. The voltage profile for
> >a normal TC along the sec is roughly linear, and only when the secondary
> >becomes coarsely space-wound with no top load does the voltage profile
> >start to bend into a quarter-sine.
> >
> >This explains why Richard Hull and others have discovered that more
> >top load is better, with no discernable correlation between the
> >operating frequency and the electrical length of the resonating coil.
>
>
> I know that above is true, but I think I remember someone posting once that
> the ideal topload, for beginning experimentation at least, I guess, was
> that topload which would lower the secondary's un-top-loaded resonant
> frequency to 0.707 of what it is when unloaded.
>
> For example: If the unloaded resonant frequency was 200kHz, then the ideal
> top-load would lower the frequency to 141.4kHz, other parameters being
> appropriate, of course.
The value of 0.707 seems like it's in the ballpark, as that would result in
half the Csec residing in the toroid capacitance. Such a loaded coil would
definitely operate in the realm of the lumped LC resonant circuit, rather than
the standing quarter-wave antenna models of lore.
I don't think that the 0.707 number really needs to be held to three digits
of accuracy, however -- IMO, probably any value from 0.6 to 0.8 would give
satisfactory performance. Richard Hull and the TCBOR have a lot of good
experience with a wide range of values, in many different configurations.
-GL