I see lots of references to SteppIR Yagi style antennas by their number
of elements but I don't know how the elements are counted. For example
how many elements does a DB-42 have? The "stock" version with no extra
6m elements, without the 80m dipole has three Trombone looking elements
and two fixed length elements, one between trombones 1 and 2 and the
second between trombones 2 and 3. So is this three elements, counting
only the adjustable on es or mis this 5 elements, counting them all?
Then with the 6m option and the 80m option added on how many elements
does it have?
Patrick NJ5G
On 4/9/2015 12:09 PM, Joe Giacobello, K2XX wrote:
I went through a rigorous attempt at modeling the four element Steppir
on all its bands several years ago. My results did not differ
substantially from those who used a less rigorous approach. I have
all of our results tabulated, if you're interested in the data.
Here's how I described my approach to the issue of wire diameter and
resistivity. (BTW, W9CF teaches physics or EE at ASU. and you can get
to the equivalent diameter calculator here:
http://fermi.la.asu.edu/w9cf/equiv/index.html).
Wire diameter
The Steppir elements are made from a rectangular perforated Cu-Be
alloy tape that is 0.56" wide and 0.018" thick. The perforations are
0.125" in diameter and there are five perforations/inch. If one
calculates the surface area of the tape, accounting for the
perforations, and then calculates the equivalent cylindrical wire
diameter, a value of 0.33" is obtained. (Based on postings on the
Steppir reflector, this is the diameter that Steppir recommends for
modeling purposes.) However, if one obtains an equivalent diameter
based on self-impedance using W9CF's on-line calculator, a value of
0.30" is obtained. Although the difference between the two
calculation methods is not major, I used the 0.30" diameter in my
models. (Since the calculator didn't account for the perforations in
the Steppir tape, I asked W9CF about their effect. He said that the
impact on equivalent wire diameter would be small and would tend to
reduce it.)
Wire resistivity
It appears that the standard Cu-Be alloy used in electronic
applications is hardened 2% beryllium, and I am assuming this is the
material used in the Steppir tape. The conductivity for this alloy is
reported as 22% ICAS or a resistivity of 4.55 times that of copper
(1.74E-8).
The W9CF calculator also provided an equivalent cylindrical diameter
for a rectangular conductor based on resistivity and the result was
0.20". I asked W9CF why this value differed so much from the
equivalent surface area calculation (0.33") and he explained that for
a rectangular conductor most of the current is confined to the edges.
Since resistance per unit length is inversely proportional to
cross-sectional area, I accounted for the effect of the resistivity
based wire diameter by multiplying the Cu-Be resistivity by the ratio
of the square of the diameters. Thus, I used a resistivity of 4.55 X
1.74E-8 X (0.32/0.22) = 1.78E-7. As you will see, the difference
between this calculated value and the resistivity of copper only
reduced gain by about 0.2 dB.
73, Joe
K2XX
Jim Lux <mailto:jimlux@earthlink.net>
Wednesday, April 08, 2015 11:54 PM
On 4/8/15 1:42 PM, Richard (Rick) Karlquist wrote:
In general, you can use a round element with circumference equal to
the width of the tape (or half the width of the tape.. opinions vary).
I just did a bunch of models of a "tape" dipole at work where we were
comparing the results from HFSS (modeling a 1cm wide tape) and NEC2
(modeling it as a tube with radius 1mm.. 0.628 cm circumference) and
they were "pretty close".
The variations from the dielectric properties of the tube will have a
bigger effect.
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Richard (Rick) Karlquist <mailto:richard@karlquist.com>
Wednesday, April 08, 2015 4:42 PM
The fiberglass tubes lower the resonant frequency by an
uncontrolled amount, since they are just fishing poles
that do not have any exact permittivity value. It is
analogous to FR-4 PC boards where the impedance is
to some extent an accident of the characteristics of
the epoxy glass. SteppIR has sourced the tubes from
various vendors over the years which further complicates
the issue. Any correction factor you would use would
be specific to a particular run of tubes. SteppIR
seems to gloss over this issue. There is a parameter
you can set on the controller that scales all elements
by a fudge factor that can be determined experimentally
for the particular copy of the antenna that is being used.
Another issue is: what size round element is equivalent
to the copper tape?
Rick N6Rk
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William Osborne <mailto:wosborne44@gmail.com>
Wednesday, April 08, 2015 4:05 PM
Does anyone have experience modelling an antenna in EZNEC and then
loading
those elements into a SteppIR antenna (I am using 4E so that is of most
interest). If you have, how does your antenna perform with your new
element
dimensions versus the factory default ones? Mine does not seem to
resonate
at the same frequency as the model, so I think a correction factor is
required to the EZNEC model elements?
Bill--K5ZQ
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