[TowerTalk] SteppIR

[Jim Thomson]

Date: Fri, 27 Feb 2015 09:00:49 -0800
From: "Steve Jones" <n6sj at earthlink.net>
To: "'Joe Subich, W4TV'" <lists at subich.com>,
<towertalk at contesting.com>
Subject: Re: [TowerTalk] SteppIR

Another thing to consider is that with a fixed multi-mono yagi design, all
the gain and F/B specs are at the design frequency.  If the design freq is
14200 KHz, then the gain and F/B degrade at 14020 KHz and 14300 KHz.  With
the SteppIR, you retune at each frequency to optimize gain and/or F/B.

Also, some of the big multi-mono yagis are considerably heavier with more
wind loading that the SteppIR because they have so many more elements on the
boom.

73,
Steve
N6SJ

##  Not quite.   The multi-mono-band yagis   have slightly enhanced gain per band
vs the mono band versions.    You can see this on the f-12 multi monbanders as well as the jk
multi mono banders...+ opti beam designs.  The 10 + 12m els  look like quasi  extra directors on 15m.  On 10m,
the 15m els behind it look like quasi extra refs.    On 20m, the 15m els look like extra dirs.  

## ur steppIR on 10 + 12m  will have a long boom electrically......vs  say 20m.   The feedpoint
Z  on 20  vs 10m will vary by  a huge amount. It will vary again depending on  how the parasitic 
eles are tuned.    Then u have the 22:50 ohm xfmr  to deal with in the steppIR.  depending on 
both spacing..and ele tuning, the Z  could easily vary  from  15-40 ohms. 

##  Do u tweak ur steppIR  for max FB, max gain,  or MIN  swr ??   No way u can optimize
all 3 of those parameters  at the same time...on one feq.   You have to compromise some where,
there is no free lunch.   Having said that, the steppir also has a lot going for itself.... like no interaction
between bands.  Flip side is  only one band can be used at one time.   Windload with only  3 els is a huge plus.
mech complexity and reliability is another issue. 

##  A fellow e-mailed me 2 yrs ago.,.who has 3 of the steppirs in a  stack.    2 of em are DOA... and the 3rd was 
just barely hanging in there.   Dunno if he had an early version or not.  He was not a happy camper. 


##  the F12  5BA  only has just ONE ele on 12m !   yet it has 5.5 dbd  on 12m.    20m is one feedline,
17+ 15m are a 2nd feedline...and 10+12m are the 3rd feedline.   20-15-10m could all be used at the same time
if required, if filters used etc.... albeit the yagi is pointed in the same direction on all 3 bands..which is no different 
than a rotary tower. 

##  f12 makes this obscure yagi..called  a N1715XL.     36 foot boom.   2 els on 17m....and 7 els on 15m.
OWA design,  with No hairpin , and just a single coax for both bands.  The 17M DE is directly driven.  There is 
a 15M parasitic DE, 13 inches away, and on both sides of the 17m DE.   8.2 dbd on 15m...and a whopping 
6.0 dbd on 17m.    The 4 x 15m dirs  act like quasi directors on 17m...enhancing the 17m gain.   A normal 2 el 17m
yagi only has 4.0 dbd.     A similar yagi is available for 12 + 10m, same concept. 

##  Its all a series of tradeoffs.  $, weight, windload, mech complexity, etc.   Stacking monobanders or dual banders is no simple feat.
The interaction  can play hell..and fast if not done correctly. 

##  Flip side is  my  F12  6el-15m monobander, on its light weight 36 ft  boom has 8.5 dbd gain, 28 db FR,,,,and is an owa design.
Dead flat swr across the entire 450 khz, no hairpin.   Gain is within .2db of the max achievable  with a 36 ft boom.  
The gain of the 6 el 15m yagi  only varies by .1db  across the entire band.  FR  only  varies by 1 db across the entire band.  It doesn’t
get any better than that.  But it only works on one band.

Jim   VE7RF