[TowerTalk] book Tribander comparison test

[Jim Thomson]

Date: Tue, 01 Mar 2011 22:22:29 -0800
From: jimlux <jimlux at earthlink.net>
Subject: Re: [TowerTalk] book Tribander comparison test


In a fixed configuration Yagi-Uda, you're looking to simultaneously 
optimize Z, Gain, and F/B, and that's hard to do over a frequency *range*.

## Not really with 4-5-6 els....esp with the OWA designs.  Then you can 
have your cake..and eat it too.  Then all that's  required is a good balun.
Those  50 ohm direct feed OWA designs are superb. 

## On 40m monoband yagi's....like my F-12  340N  [ 85%  full size]...I used 2 x vac 
relays  per el....to give me 3 x   'segments' . 2 x small tubing coils  are used  for each el,and
each can be shorted out..one at a time.   Then you can really optimize the yagi.  Dunno why 
F-12  used aprx 59'  for the REF..then 53'  for the DE..then 51'  for the DIR  in the original design.
The 3 x els are all built the same way....except  for the  3/8"  tips.  It's better  to make em all 59'
long..and then just use LESS Linear loading on the DE  and DIR. 

##  Mike at  Seco systems is building me a custom  80-D  Tornado drive  for my rebuilt  F-12
80m rotary dipole.   It uses a pair of  motor driven compressible coils at the feed-point. Coils are
made from 1/4"  OD  plastic coated Cu tubing.   I tossed the stock linear loading wires..and replaced
em  with a combo of the compressible coils  +  a  pair of 17.5' capacity hat's  [aka T -bars] . A single
new  5/16"  double braided dacron line is used for a truss..since no more LL  wires.  End result is..the
stock 68' long rotary dipole  will tune dead flat..across 900 khz. [3200-4100  It's tweaked, such that the coils
are slightly un compressed at 3500..then are even more uncompressed  at 4 mhz.  The mating SDC-102
controller is just a 4 x digit, digital turns counter..with 10 x pre-sets.  A small 5 x turn  tubing coil is used for the
hair pin. Of course a good balun will be used. 
      




If you've got Matlab or Octave, you can get some nifty stuff from 
Sophocles Orfanidis's web site that lets you simulate and optimize this 
kind of thing in an idealized sense.  Or you can download 4nec2, and let 
Arie's optimizer grind on it.

These days, computers are so fast, that you can run a dozen cases in 10 
minutes.  Sure, you can find pathological cases, but for the most part...

##  I used to spend hrs on end  with YO-4.0    then YO-6.03  etc.  I also tried 
yagi-max, etc.   A buddy got me to tweak the els on his old Telrex 3-el 20m  monobander
years ago..and optimize it  for  14.000  to 14.250    El positions on the telrex  are fixed of course,
so only the tips can be tweaked.    After the next contest, he was VERY impressed with the results. 
Same deal with the telrex 6-el  20m yagi.... [which used equal spacing between all els..and I think most of the
directors  were all the same length.]   Same results.  

##  Then I got into taking all these old  w6sai designs, and old hand book stuff..and also most of the old wilsons,hy-gain etc,
and re-tweaked em all on YO.    I 1st modeled them stock...then  compared the stock  performance numbers  to the
tweaked up version. What a huge difference!  

##  I looked at the  earlier StepIr  yagis'....when they 1st came out.   I was not 100% satisified with the mechanical's
back then. I would not be trying to stuff  YC-156  power levels through that built in balun they use either.  A buddy
bought the Monster IR... and his new OR-2800  rotor lasted exactly 9 x days b4 it was destroyed, chewed to bits.
I know another fellow  who has  3 of the  36'  boom  stepir's...stacked on one tower, with ring rotors on the lower 2 x ants.
2 of the 3 stepir's have packed it in..and the 3rd one is hanging in..barely.   I'm sure once the bugs are all out of em, that
they are probably an excellent option.  LPDA's are another option..but poor at best..unless they are really big. 

##  it's a series of tradeoff's in the end.  I don't operate 10/12/6m  anymore... so the focus is  80-15m.  17/15m is on 
one boom.  Everything else is monobanders.  LPDA's  and  monsterIR's  that cover 40m  are both out of the question,
so the remaining options were used....albeit no 12-10-6m.   12-6m  can always be  added on a ring rotor anyway, so no 
big deal.  I just lost interest in those bands years ago...esp after  39 yrs. 

Later... Jim   VE7RF    
      


> If so, not correct.
> 73
> Barry ZL1DD
>