Date: Tue, 01 Mar 2011 22:22:29 -0800
From: jimlux <email@example.com>
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
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
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
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.
> Barry ZL1DD
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