[TowerTalk] Modelling SteppIR Elements

Thu Apr 9 14:30:55 EDT 2015

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 at 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 at 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 at 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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