That sounds about right as Mosley claims a gain of 4.5DBd for their TA32 which
has a boom length of 6 feet but it uses a reflector instead of a director.
Is there a reason why 2 element yagis that are commercially made use a
reflector instead of a director? I seem to remember from the ARRL antenna book
that you can get slight more gain from a director. Also, the windloading would
be slightly less with a director, as would the cost of materials since the
director is shorter than the reflector?
73s John AA5JG
--- On Wed, 9/23/09, Terry Conboy <n6ry@arrl.net> wrote:
> From: Terry Conboy <n6ry@arrl.net>
> Subject: Re: [Antennaware] Small Tribander or SteppIR 2-element?
> To: RLVZ@aol.com
> Cc: antennaware@contesting.com
> Date: Wednesday, September 23, 2009, 2:44 PM
> 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@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
> >
> >
> _______________________________________________
> Antennaware mailing list
> Antennaware@contesting.com
> http://lists.contesting.com/mailman/listinfo/antennaware
>
_______________________________________________
Antennaware mailing list
Antennaware@contesting.com
http://lists.contesting.com/mailman/listinfo/antennaware
|