I don't know that Method of Moments codes (i.e. NEC) adequately model
parasitic capacitance effects, which are proabably important in loading
coils). No question that using a GH (helix) to model the turns works, at
least as far as the inductive coupling goes. NEC doesn't deal with skin
effect either.
But, on the other hand, if you're expecting better than 1% accuracy with NEC
for a ham antenna (in a typical ham installation), you're probably dreaming
anyway. If someone's willing to send me a set of validated and accurate
numerical greens function file for my VW Passat, though, I'm willing to go
up to the antenna range and do some tests.
Jim, W6RMK
----- Original Message -----
From: <K3BU@aol.com>
To: <towertalk@contesting.com>
Sent: Saturday, November 22, 2003 7:48 PM
Subject: Re: [TowerTalk] On the phase shift in current between ends of a
coil
> In a message dated 11/22/03 11:04:13 AM Eastern Standard Time,
> jimlux@earthlink.net writes:
> >>I think it's best to leave it at:
> Loading coils are not isolated lumped elements and cannot be modeled as
> such.
> A lumped model serves as a decent design tool to determine a starting
point,
> which will have to be further iterated empirically.
>
> To give credit where it's due, the research work I've described above was
> primarily done by Terry Fritz (in the US), Paul Nicholson (in the UK), and
> Antonio Carlos M. de Queiroz (in Brazil). I can come up with some links to
> papers if needed.
>
> Jim W6RMK<<
>
> where he states the following and then goes into the case of modeling real
> life helix and investigating its property and NEC modeling.
> >>As a consequence, few modelers have explored the behavior of helically
> wound single layer solenoid inductors in their models--simply because
winding a
> coil is too laborious a task relative to using the loading facilities
built into
> NEC. We have presumed that the loads--especially Type 0 series R-L-C
> loads--adequate specify the loads we need.
> Yet nagging suspicions remain about such loads. The current differential
that
> is present at each end of the load suggests that--like their linear load
> counterparts--these loads do not act like pure inductances, but may also
function
> as simple current bearing wires. Models of helical dipole elements show
very
> usable gain, which parallels the experience of those who have constructed
such
> antennas. I guess we shall not know whether mathematical models of loads
> accurately reflect the operation of single layer solenoid inductances
unless we
> actually wind some model coils and replace the Type 0 loads with them. <<
>
> Yuri, www.K3BU.us
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
>
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_______________________________________________
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Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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