Date: Wed, 13 Oct 2010 05:43:17 -0700
From: "Jim Thomson" <email@example.com>
Subject: [TowerTalk] Sigma 280-S
I'm considering the 180S or 280S also, likely the shorter (not Magnum)
versions. The Tornado variable pair of inductors at the feed point
(squeeze/expand the coils) appears to be a good idea at least for the
dipole, and should be easy to set, using SWR.
It would also seem to be possible to make a pair of Tornados work for
the 2L beam, but with two sets of variable inductors the tuning might be
a nightmare to figure out. Moving around the 70Khz bandwidth would be a
real plus. With enough L range, it might tune to some other band, but I
won't even go there, other than to suggest it might provide some
detuning/decoupling from adjacent yagis.
So, are there any Tower-Talkians with experiences or models with either
of these setups?
## The control box for EACH Tornado drive comes with 10 x pre-sets. Each
box also has a 4 x digit, digital turns counter. The digital turns counter
counts the turns
of the big threaded delrin lead screw, that goes down the middle of both
coils. It also has a
'park' mode, where it compress's both coils fully, and re-sets the counter to
ZERO. [ max inductance]
OK, then it's easy to tweak the DE..1st for resonance. Then, the REF will
always be tweaked slightly lower in
freq than the DE. The turns counter for the REF will always be a lower number
on it's digital counter
VS the DE. Once the REF is tweaked for max F/B... for say 3800... then the
REF turns counter readout
is entered into say memory #1. The turns counter for the DE is entered into
it's own control box,
also memory #1. Then re-tweak both the DE +REF for a new freq... then
enter both of em into memory #2, etc.
## You only have 10 x memories[pre-sets] per controller. For the in between
freqs, you can take note of the turns
counter readings..and log em. Then bring up the closest pre-set.... then
manually tune to the logged readings.
On paper, one should be able to tweak the 280-S for max gain, max F/B and
flat swr across the entire band.
The big advantage here is.... both els can be adjusted from the shack...and
with the 2-el yagi at full operational
height... VS crank up tower at min height. I have been talking to both Mike
at Seco systems who makes the Tornado
drives and also Mark @ F-12. All 3 of us think it's doable. If a
SPST-NC vac relay is added to each ele, and a 2nd
coax+balun run to the REF [ and routed to spare port on remote ant switch
box], then the DE can be opened off, and
REF tuned up dead on any freq u want. The REF can also be opened off, and
DE tuned up on any freq. You can then
do cool stuff, like open off the REF, and make it instantly BI-directional
[and also do an instant F/B check].
You can also tune the REF higher in freq than the DE... and reverse the
pattern , without rotating the array ! [ it's
now a DE-DIR].
## The Ameritron / MFJ screwdriver controller is what Mike uses to control the
Tornado drive. The Tornado drive
not only has +/- inputs for the reversible motor, it also has a 2nd pair for
the digital turns counter. So to pull this off
requires a 280-S... with a tornado drive on both els, and 2 x controllers.
The hairpin still needs to be manually tweaked,
but that's a minor issue. I'm hell bent to try this config next spring. I'm
convinced it would kick butt..with it up 100'
My concern was if the 80m array will screw up a 20m array below it. Even if it
did, both vac relay's on the 280-S
could be operated, and then both REF and DE could be opened off, when
operating on 20m...end of problem.
&&&& As a side note, seco makes a shorting switch version of the tornado
drive. If you blow up the pix on their site of the
coils when expanded, they use a brass plunger..that engages a tapered
cylinder..when the coils are fully compressed. One plunger
per each coil. It was originally used on the Sigma80 vertical. With the
coils shorted out, presto, the 80m vertical is now resonant on 40m !
[albeit not tunable] The shorting switch on a 280-S could be used to
eliminate any interaction between 80 + 20m. Just put both controller's
in the 'park' mode... and they will fully compress all 4 x coils and short
all four of em out. [ and also re-set the counter to zero.] My only
concern would be the V drop across those coils is wicked... and may arc the
plunger, just prior to it engaging. This might happen if on the low
end of 80m CW band.... where the coils are almost fully compressed. It might
not be a problem. On possible "fix" might be to add 1-2 extra
turns to the coils, so when on CW band, they are never close to fully meshed.
I'll see what mike at seco thinks abt this. Stay tuned.
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