[Antennaware] Small Tribander or SteppIR 2-element?

[Terry Conboy]

I created a model of a 2-el yagi on 20m with 6' spacing and the gain in 
free space is 6.71 dBi (4.56 dBd).  F/B is 17 dB.  This is with the 
parasitic element tuned as a director.  The feed Z is 22 ohms, which the 
SteppIR transformer matches to 50 ohms.  The 2:1 bandwidth is about 240 
kHz, but that's not an issue with the SteppIR, of course.  I assumed 
0.35" diameter copper elements, which are only down 0.06 dB from 
lossless conductors, so the efficiency is pretty good (98.6%).

Increasing the spacing to 12 feet gives max gain with a parasitic 
reflector.  The gain is 6.82 dBi (4.67 dBd) but the F/B is only 6 dB.  
Feed Z is 35 ohms (a good candidate for a hairpin match to 50 ohms) and 
the 2:1 bandwidth is 410 kHz.  Using lossless elements increase the gain 
by 0.05 dB, so the efficiency is 98.8%.

It appears the SteppIR 2-el is a good compromise on 20m for limited 
space, other than cost.

73, Terry N6RY

On 2009-09-22 12:31 PM, RLVZ at aol.com wrote:
> I had great results with a SteppIR 3-element up 60' when  the antenna 
> worked as designed.  Unfortunately, the Controller was bad  upon arrival, and 
> then an 80mph windstorm blew two fibreglass elements off the  antenna which 
> then allowed water into a Stepper motor and it went  bad!
>  
> Perhaps I'm a glutton for punishment but I'm seriously  considering a 
> 2-element SteppIR at a temporary QTH in the Midwest as the  3-element SteppIR 
> turning radius may not clear the trees.  Question: isn't  the short 6' boom on 
> the 2-element SteppIR too short for good  results on 20-meters?  I am not 
> familiar with using  modeling programs and don't have the time to learn so I'd 
> appreciate your  thoughts on this.
>  
> A 3-element tribander will work at this temporary site as it  has about the 
> same turning radius as a 2-element SteppIR... and a Tribander  like the 
> Hy-Gains TH3 might perform as well or even better better on 20-m.  (on the 
> portion of the band that it is tuned for) as it has a  little longer spacing 
> between driven element and the reflector.  Of  course the Tribander would be 
> alot cheaper too.
>  
> What's your thoughts on the efficiency of a 6' boom length for  a 2-element 
> 20-m. yagi?
>  
> 73,
> Dick- K9OM
>
>