[TowerTalk] lp V stepIR

Sat Jan 23 16:36:59 PST 2010

Another side thought on LP's -
Obviously not a consideration v the SteppIR, but the LP is pretty straight 
forward for ththe DYI guy who wants to build his own. Somewhat of a 
carryover from before there were as many good yagi design computer programs. 
With the LP you don't have to decide tradeoffs betwen gain and F/B. You 
pretty much cut to formula and get what you expect. When I did mine on the 
PC I did fudge it a bit to try to favor the ham bands but I'm not sure that 
it really bought much extra.
Gene / W2LU

----- Original Message ----- 
From: "Joe Subich, W4TV" <lists at subich.com>
To: "'Scott McClements'" <kc2pih at gmail.com>; "'Tower and HF antenna 
construction topics.'" <towertalk at contesting.com>
Cc: <k2vi at cox.net>
Sent: Saturday, January 23, 2010 7:15 PM
Subject: Re: [TowerTalk] lp V stepIR

> Now, before we fire up the LPDA crowd again -  when the LPDA
> array's boomlength gets to around ~36 feet or greater  with
> 20 elements, and covering only  14-30Mhz,  the LPDA starts to
> kick serious butt.  You start to see gain around 7.5dBi, but
> more importantly the F/R ratio is up around 25dB across all
> the bands (OWA Yagi style).

Except when we get to 36 foot booms a yagi is capable of 10 dBi
on 20 meters (4 element) and 11.5-12 dBi on 10 meters (6 elements).

Not to bang the SteppIR drum too loudly but the 4 element antenna
(36 foot boom) does exactly that 10 dBi/25 dB F/R on 20 and high
11 dBi with a little lower F/R (not enough elements) on 10 meters.
A good OWA design (5 elements on 20, 6 elements on 10) will also
provide those gain figures.   With 20 elements to play with, the
Force 12 "multi-monoband" type designs are also competitive
performers when the boom length gets longer.

I have nothing against log-periodic antennas but they are not
the most efficient use of boom length, wind load or weight.

73,

   ... Joe, W4TV

> -----Original Message-----
> From: Scott McClements [mailto:kc2pih at gmail.com]
> Sent: Saturday, January 23, 2010 2:29 PM
> To: lists at subich.com; Tower and HF antenna construction topics.
> Cc: k2vi at cox.net
> Subject: Re: [TowerTalk] lp V stepIR
>
>
> I also put together a 18 foot boom/ 8 element NEC4 model
> using the ARRL LPCAD program. My gain figure for the LPDA
> were a little higher (5.5dBi), but  I agree with what is
> shown here. Also note, its no contest on the F/R ratio.
>
> Now, before we fire up the LPDA crowd again -  when the LPDA
> array's boomlength gets to around ~36 feet or greater  with
> 20 elements, and covering only  14-30Mhz,  the LPDA starts to
> kick serious butt.  You start to see gain around 7.5dBi, but
> more importantly the F/R ratio is up around 25dB across all
> the bands (OWA Yagi style). Cebik has a model his site on a
> 52 foot boom / 22 elements  that is around 8.6dBi and the F/R
> peaks around 37 dB (!!!) on 20 meters. The LPDA is a superior
> multiband beam once the the boomlength is allowed to grow.
>
> However, for these "short" boomlengths (say 24 feet and
> under), there are many other parasitic type beams in the
> market that provide more raw performance than the LPDA. As
> you see from Joe's chart, the difference is smaller on 20
> meters, but as you go up the bands, the Steppir uses the
> boomlength more effectively.
>
> -Scott, WU2X
>
>
>
> On Sat, Jan 23, 2010 at 2:02 PM, Joe Subich, W4TV
> <lists at subich.com> wrote:
> >
> >> 3 element stepir and the t8 will radiate almost the same signal
> >> strength at the other end.
> >
> > Both modeling and theory strongly disagree with this ...
> >
> > The active portion of an 8 element 13-32 MHz LP on an 180
> foot boom is
> > a small portion of the total boom length. Here are model
> data of an 8
> > element LP (18 foot boom), the SteppIR 3 element yagi (16
> foot boom)
> > and Force 12 C3E (extra 10 meter director and 18 foot boom).
> >
> > The SteppIR/3 vs. 8 element LP vs. C3E (free space):
> > ---------------------------------------------------------
> > LP SteppIR C3E
> > Band Gain F/R Gain F/R Gain F/R
> > 20 5.0 9.2 7.4 25 6.6 10
> > 17 4.9 12.3 8.3 25 3.0 2
> > 15 4.8 13.0 8.5 20 6.2 11
> > 12 5.0 14.9 8.8 15 4.4 5
> > 10 5.1 14.5 9.0 11 7.4 23
> > 6 n/a 10.1 20 n/a
> >
> > The Log Periodic is a simplified model of an 8 element
> design on an 18
> > foot boom. K9LA's work with the T-6 shows about .5 dB less
> gain for a
> > shorter (12 foot boom) antenna while Preliminary
> (unverified) results
> > for a 10 element model (24 foot boom) show about .8 dB
> additional gain
> > and 1-2 dB better F/B (model data from AO).
> >
> > The SteppIR/3 vs C3E numbers closely parallel the field test data
> > published by N0AX/K7LXC and SteppIR.
> >
> > One can see that the LP fails to come even close to the SteppIR
> > - falling short my more than 3 dB except on 20 meters.
> Further, falls
> > one to two dB short of the typical gain of a two element
> > (Reflector/Driven with 50 Ohm feed).
> >
> > An LP is a poor trade-off unless you have excess power and need to
> > operate on any frequency instead of the relatively narrow amateur
> > bands.
> >
> > 73,
> >
> > ... Joe, W4TV
> >
> >
> >
> >> -----Original Message-----
> >> From: towertalk-bounces at contesting.com
> >> [mailto:towertalk-bounces at contesting.com] On Behalf Of anthony
> >> Sent: Saturday, January 23, 2010 9:45 AM
> >> To: towertalk at contesting.com
> >> Subject: [TowerTalk] lp V stepIR
> >>
> >>
> >> 3 element stepir and the t8 will radiate almost the same signal
> >> strength at the other end.More to fail with the stepir and did you
> >> see how much they cost??? WOW. big bucks. I would put up
> the t-8 and
> >> high grade coax like davis bury-flex. If done right this
> antenna will
> >> stay up without any maintenance for 20+ years. No way the step ir
> >> will do the same. Also you can buy two t-8's and one yaesu
> g-800s for
> >> what you would pay for a stepir. Just a thought.
> >>
> >> tony k2vi
> >> _______________________________________________
> >>
> >>
> >>
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> >
> > _______________________________________________
> >
> >
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> >

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