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Re: [TowerTalk] lp V stepIR

To: "'Tower and HF antenna construction topics.'" <towertalk@contesting.com>
Subject: Re: [TowerTalk] lp V stepIR
From: "Joe Subich, W4TV" <lists@subich.com>
Reply-to: lists@subich.com, "Tower and HF antenna construction topics." <towertalk@contesting.com>
Date: Sun, 24 Jan 2010 01:20:56 -0500
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>

> 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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