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@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@contesting.com
>> [mailto:towertalk-bounces@contesting.com] On Behalf Of anthony
>> Sent: Saturday, January 23, 2010 9:45 AM
>> To: towertalk@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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