This is true, but the cool thing about the LPDA is the gain *and* F/R
go up. My point about the 36 foot long boom is that you truly have
the gain of a 3 element yagi over the entire frequency range and you
get good (25dB) flat F/R performance over the frequency range that
even rivals some monoband yagis. Go even longer than 36 feet and you
get more gain and more F/R without trading one for the other. It
might sound like a lot of money to build a 48 or 52 (~8.5dBI) foot
boom antenna, but its a lot cheaper than five 4 element monoband yagis
from M2 and you would really have that kinda of performance, whereas
the SteppIR or interlaced Yagis will always suffer some performance
shortcoming (usually F/R). To boot you can mount the large LPDA up at
the highest point on your tower instead of having to stack monobanders
on your tower.
Let's not act like the SteppIR is the perfect monobander - the fixed
element spacing and fixed feedpoint impedance of 22 ohms *is* a
limitation. The SteppIR doesn't match a high performance monoband
yagi on every frequency, as can been seen by the lower F/R on the
higher bands (esp. 10 meters). You aren't free and clear to pick any
design you want, because if you desire a low SWR, you have to come up
with a element length combination that has a ~22 Ohm feedpoint
impedance. It definately provides good bang for the buck with respect
to boomlength. But if I had a single tower to work with, I think a
stack of well built large LPDA could outperform any other type of
multiband antenna.
I would pick an Optibeam, SteppIR or maybe a Force 12 for any
boomlength under 24 feet though.
-Scott, WU2X
On Sat, Jan 23, 2010 at 7:15 PM, Joe Subich, W4TV <lists@subich.com> wrote:
> 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).
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