[Towertalk] antenna advice

[Steve Jackson]

Pete W1RM wrote:

>>The ice storm of late November has given me the 
>>opportunity to replace
>>all my antennas (translated, mother nature smashed
>>all of them).  I had
>>been using a Cushcraft 402 and a Tennadyne T-10 at
>>100 and 90 feet
>>respectively.  They worked OK.  

The December 4 ice storm here in NC snapped the boom
of the upgraded-wind survival version of my Force12
C36XR, just behind the 6th element.  Actually, it was
the boom truss that did it in; the cable snapped where
it had frayed at the mast clamp.  Next time I will use
a better way of securing the truss.

After much hand-wringing, I've decided on replacing
this antenna with a C-31XR and a separate rotatable
dipole.  In the case of the dipole, I will probably
get the beefy M2 model.  (A dipole, other than the
structural aspects, is still pretty much a dipole.)

Why these choices?

I bought both the 'LXC test book and EZNEC.  I spent
hours fiddling with the modeling and patterns, and
comparing the projected outcomes versus my experience
here with the similar C-19XR (the front of the C36)
and the reports of others.  I also talked, for hours,
with nearly a dozen hams, many of whom are reading
this posting.  To all, a sincere thanks for helping me
build the best station I can build.  You'll be happy
when I whup you in the next contest ;-)

I wanted a bit better performance on 20-15-10 than I
had with the C36.  Not that it was bad in any way, but
I, Mr. Hercules II amp, lust for more ERP.  So, going
to the bigger boom version of what I already had is a
win there.

The 2 el. 40M section of the old antenna was OK, but
no great shakes.  At 80', it worked well enough for me
to want to replace it, but size and cost rule out a
proper-size boomed 40M yagi.  A dipole will do for my
interests.  The Force 12 EF140N is an interesting
choice, but I'd like to try the M2 model to see what
KC1XX is always crowing about, in terms of their
structural design.  Plus, Mike and others at M2 are
just the best bunch of guys you'll ever send your ham
radio money to.

Since the SkyHawk needs three feedlines, and my
switching arrangement only has one for the tribander,
that was that.  

I elected to not go with a log-cell design antenna,
because I want in-ham-band performance.  The LPs
(Sommer, Tennadyne) present too much of a compromise
for me there.  If I did MARS, or was the FAA, well,
maybe I could see why I'd want a log.  But I don't
anymore, and I'm not.

Quads?  Ummm, I'm writing this because I had an
ice-related antenna failure on an 80' tower that
doesn't crank down for service.  'Nuff said for that.

Trapped antennas, like Cushcraft, HyGain, and Mosely,
modeled too oddly for me.  I can't ever be sure I got
any of it right!  And in this day and age, low-loss
designs using full-size elements per band just makes
too much sense for me.  The KT36 was intriguing, but
mechanically too complicated for my tastes, and not
all that persuasive in terms of raw performance.  I've
already had a simple mechanical problem take down a
two-kilobuck antenna.

Pre-emptive SteppIR comment:  read the previous
sentence about six times before you ask me to
reconsider this antenna.  I don't live in Phoenix.

Regarding Force12 as a recurring theme: I'm no "Tom
Toady" here ... let me be straight right up front.  I
find his west-coast customer support spotty and
disorganized.  His QA is more "Fiat" than "Honda." 
Natan is helpful, but relies entirely too much on Paso
Robles, which is generally asleep at the wheel.  When
Tom moved from Santa Clara down south, instead, he
should have moved someplace else and got himself a
staff of helpful hams.  (There.  I said it.  N6BT: 
care to comment?)

Nevertheless, I am buying an antenna, not stock in
F12. 

I have dismissed two technical arguments against the
F12 unit:  they were (a) it has a 'weird' feed system
and (b) structural/mechanical integrity.

For point (a), my personal good experience with the
sleeve and hairpin feed on the C19 portion of the C36,
coupled with recent purported C31
assembly-and-materials improvements (can someone
confirm this?), caused me to dismiss this concern. 
The feed-style issue, if there even is one, is small
when compared to the other benefits.  I will note that
minor icing did cause temporary detuning of my C36 in
the past.  I suspect it was the ice ball stuck on the
hairpin, based on binocular inspection.  It melted,
and it was fine afterwards.  This wasn't a major
problem for me as it happened only once.  Your mileage
may vary.

As to point (b), I will note that the C36 boom failure
was due to the sudden snapping of the compromised
truss cable, with an antenna that had 1 1/2" to 2" of
ice on it.  Gee.  How does one design against THAT?

I'll also note that the 40M end of the boom IS STILL
INTACT - even after the snapped cable incident, and
its obviously larger mass and ice load.  Clearly,
YagiStress works.  And, the F12 EF706 and F12 N1217
above the C36 were completely unscathed by the ice
load.

Pete, I don't know if any of this helps you.  But I
wanted to respond with some thoroughness.  Let us all
know what you end up doing.

GL es merry Christmas.

Steve KZ1X/4
Chapel Hill
Go Tar Heels


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