[TowerTalk] Help in planning a new QTH

[Joe Subich, K4IK]

N2IC writes: 

> 
>  From Dave Hachedorian's (K6LL) posting:
> 
>  > Once you do the conversions, the claimed
>  > gain is as follows:
> 
>  > Band    4el Steppir    C31XR
>  > 20        9.5dBi        8.1
>  > 17        10.0            -
>  > 15        10.2          8.4
>  > 12        10.4            -
>  > 10        10.6          9.5
> 
> Those Steppir gain figures are very questionable.  They are 
> significantly higher than the gain figures for optimized yagi 
> designs in the 20th edition of the ARRL Antenna Book.  While 
> a Steppir may be a fine antenna, it's still just 4 elements 
> on each band, and won't be any better than an optimized 4 
> element beam on the same boom length.

The SteppIR gain figures are confirmed by both YO and EZNEC. 
They represent achievable gains with a 22 Ohm feed impedance 
for four elements on a 32 foot boom and (relatively) narrow 
bandwidth.  Feel free to model the antenna for yourself and 
you will find, for example, gains (free space) between 9.3 dBi 
and 9.6 dBi on 20 meters.  

> 
> For another comparison:
> 
> Band   Optimized 4-element from ARRL Antenna Book
> 
> 20            8.5 dBi (26 foot boom)
> 17            8.5 dBi (20 foot boom)
> 15            8.2 dBi (18 foot boom)
> 12            8.5 dBi (15 foot boom)
> 10            8.3 dBi (14 foot boom)
> 
> Now, you could argue that the Steppir has the 4 elements on a 
> longer boom, so let's compare to an optimized yagi with 
> approximately the same boom length:

The ARRL Handbook antennas were "optimized" for 50 Ohm SWR < 2:1 
and F/B > 20 dB across the entire amateur band.  Maximum gain is 
traded for both the 50 Ohm feed impedance and higher F/B. 

> Band        Optimized N-element yagi from ARRL Antenna Book
> 
> 20           9.2 dBi (34 foot boom, 5 elements)
> 17           9.8 dBi (30 foot boom, 5 elements)
> 15           10.8 dBi (36 foot boom, 5 elements)
> 12           10.8 dBi (30 foot boom, 6 elements)
> 10           11.6 dBi (36 foot boom, 6 elements)
> 
> I would have to conclude that the Steppir manufacture's gain 
> figures are inflated on 20 and 17 meters.  

Again, these antennas are "optimized" for 50 Ohm feed impedance 
and F/B not gain.  Stop comparing apples and oranges ... look 
at the large body of research and you will find gain climbs 
significantly with lower feed impedance.  It's simple physics: 
lower impedance => more current => more radiation => more 
radiation => higher gain. 

73, 

   ... Joe, K4IK