Re: antenna impedance - calculated 10 - 20 Ohms - measured 36 Ohms??
- From: "Frank" <ve6cb@xxxxxxxxxxxxxxxx>
- Date: Wed, 01 Mar 2006 04:25:04 GMT
"Roy Lewallen" <w7el@xxxxxxxxx> wrote in message
news:12082j8tknvfi05@xxxxxxxxxxxxxxxxxxxxx
dansawyeror wrote:
Thanks - I will try to figure you how to create a non lumped model for
the inductors. Right now that is 'undiscovered country'.
EZNEC v. 4.0 users should use Wires Window/Create/Create Helix. You'll get
many choices, including position, orientation, various ways of specifying
the pitch and number of turns, twist direction, and so forth. (EZNEC demo
users can create any size helix to see how it works, but won't be able to
run a calculation unless the helix is extremely simple.) In NEC, use a GH
'card'.
There should be at least a wire diameter of air space between turns,
preferably several. (That is, the center-center distance between the wires
in one turn and the wires in adjacent turns should be at least two wire
diameters, preferably more.) If air spacing is less than 2 or 3 wire
diameters, the calculated loss will be somewhat lower than reality because
NEC (or EZNEC) doesn't account for proximity effect.
Roy Lewallen, W7EL
As I understand NEC; large errors can be introduced by junctions of
dissimilar wire diameters, and in particular when the wires are at 90 deg.
Therefore, when you have designed your "GH" inductors, the rest of the
antenna should by constructed of the same diameter wire. This may be
difficult since Dan is using two coils of significantly different Qs. I
guess you could overcome this problem by varying the conductivity of the
inductor to obtain the desired Q. Also, since segmentation tends to be
relatively high in a helix, should segment length tapering be applied to
those segments adjacent to the helix?
Frank, VE6CB
.
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