Message-ID: <004601c51fd1$5aade960$0d540150@p2300>
From: "captbrian" <captbrian@ukonline.co.uk>
To: rsgb_lf_group@blacksheep.org
References: <6.1.0.6.2.20050301115700.03662eb0@mail.casema.nl> <004d01c51e98$ec121f00$c401a8c0@quaycustomer> <000601c51f6a$c8687310$e901a8c0@bob2l2u6k2n1g3>
Date: Thu, 3 Mar 2005 09:14:06 -0000
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Subject: LF: Re: Re: Re: Current "lost" in loading coil
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Thanks Vernall but..

<<"it will be some Q times the voltage applied at the "cold end". ">>


Where would you measure this?   ..... there isnt any "voltage applied at the
cold end". [It is plugged into the finest earth that cunning hams can
devise.]  The voltage at the "colder " end depends where you tap (if that is
how you feed )?   Or am I wrong ?

If fed with a coupling coil I confess I am lost .

Bryan   50 50 N / 00 16W


----- Original Message -----
From: Vernall <vernall@xtra.co.nz>
To: <rsgb_lf_group@blacksheep.org>
Sent: Wednesday, March 02, 2005 8:58 PM
Subject: LF: Re: Re: Current "lost" in loading coil


> Hi all,
>
> The discussion has brought out some interesting points on what goes on in
a
> practical loading coil.  I would like to investigate (measure) some vector
> relationships of current and voltage on a practical setup, but in the
> meantime I am occupied with preparing for an LF DX weekend at Quartz Hill,
> so it will be a while till I can find time to do quantitative testing.
I'm
> interested to find out if maximum current in to the "cold end" of the
> loading coil corresponds with maximum radiation (far field, not near
field)
> from the system (system being not only the wire connected to the "hot end"
> of the loading coil).
>
> One can expect a big difference in relationships between tuned and
untuned.
> When tuned (the usual situation for LF transmitting) one can expect an
> approximate linear voltage rise (similar volts per turn) and at the top
"hot
> end" it will be some Q times the voltage applied at the "cold end".  If
> there is similar stray capacitance per turn, then the current "lost" has
an
> approximate linear distribution up the coil, as "lost current" is
> proportional to driving voltage, which increases along the coil.
>
> There will also be a phase shift due to physical length of wire in the
> inductor, with 360 degrees corresponding to a wavelength (even for
applying
> DC, there is a finite time from applying excitation at one end till
current
> comes out the other end, it is the "propagation delay" that forms the
phase
> shift for steady state sinewave excitation).  A coil winding length of 100
> metres of wire is about 4.5% of a wavelength, or some 16 degrees for 136
> kHz.  The stray capacitance will of course modify the ideal situation of
the
> 16 degrees being proportional to length along the winding, especially
around
> the upper part of a resonant coil where the voltage is highest.
>
> 73, Bob ZL2CA
>
>
>
>