> Let's not act like the SteppIR is the perfect monobander -
I don't think that anyone is ... although I think the four
element SteppIR has to be about the best single antenna
20-6 meter solution available. I'd like to try something
similar to the 80 meter dipole (from the DB36) with the four
element 20-6 antenna for 40 and 30 meters instead of the folded
driven element. I think it would be much more reliable than
the "trombone" and it certainly does not need any loading
coils like the 80/75/60 meter version for the DB36.
> the fixed element spacing and fixed feedpoint impedance of 22
> ohms *is* a limitation.
The fixed element spacing is a limitation in that it effects
the F/B on 10 and to a lesser extent 12 meters. However, the
220 Ohm feed is not a limitation since that is very close to
the feed impedance for maximum gain with a minimum number of
elements.
It would be interesting to add another passive element between
the driven element and reflector and try some "dual reflector"
designs for 12, 10 and 6 meters. I suspect forward gain would
drop slightly (shorter effective boom length due to reduced
current in the "back" reflector) but the F/B would improve a
good bit. On the other hand, F/B is not that important for
me here in Florida <G>.
73,
... Joe, W4TV
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com] On Behalf Of Scott
> McClements
> Sent: Saturday, January 23, 2010 8:12 PM
> To: lists@subich.com
> Cc: k2vi@cox.net; Tower and HF antenna construction topics.
> Subject: Re: [TowerTalk] lp V stepIR
>
>
> 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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