Date: Wed, 15 Jun 2016 02:10:21 -0400
From: "Roger (K8RI) on TT" <K8RI-on-TowerTalk@tm.net>
To: "towertalk@contesting.com" <towertalk@contesting.com>
Subject: [TowerTalk] OWAs or Fans?
I have several center fed, half wave sloping dipoles for 80 and 40..
I'm debating on putting up several 80 meter OWAs, or just making the the
Fans for 80 and 40. On 40, I can get away with RG8X at the legal limit,
but not on 75/80.
However I only operate below 3.7 and 7.200.The SWR remains relatively
low, below 7.2 and easily compensated for with the AT5K-HP and the 8X
handles it nicely. With 80, 3.7 to 3.5 is a different story, but the
tuner still handles it nicely. OTOH the voltage might be a tad high for
8X with the high SWR. Still, using LMR 400, or the heavier BuryFlex(TM)
will work and I "think" I can get enough turns through 7 cores, with the
coax bundled instead of equally spaced turns around the cores, to tame
the common mode RF. If not, I can add a second choke as I have now.
I'm leaning toward the fan instead of the OWA as I can get 5 slopers as
in the antenna book for switchable directivity with a f/b ratio? The
ones to the NE and SE would be hidden by the trees. Hopefully I can get
the desired results with a single choke at each feed point. That's a
whopping 35 cores. A second 5 core takes it up to 60 cores as well as
adding up to a lot of coax! For the 7 turn at roughly 21 feet the 5
chokes add up to about 105 feet and about 80 feet (I've not calculated
that yet) is another 400 feet. I probably shouldn't have given so much
used LMR400 away. I might still have 400 or 500 feet left. I do have a
new, 500 ft roll of BuryFlex, but I need a 100 feet of BuryFlex to get
from the AV640 under the sod to the tower grounding plate and then to
the 6-pack.
Has anyone modeled one of these setups just using dipoles on any band?.
--
73
Roger (K8RI)
## The older arrl books claim, with 5 x 1/2 wave slopers, aprx 20 db FB..and
some
gain..like 3-4 db. If you do the CM choke right, you wont require 35 x
cores...nor 60. I talked to
a fellow who used the 5 x sloper system years ago, and the 20 db FB was
something to behold.
That was on 40M. IMO, it was a superb ant. Never heard one on 80m, but if
the support was
high enough, it too should work good. A bit of gain..and 20 db FB..with
instant 72 deg switching,
would make most folks happy.... and no yagi / hd rotor to mess with.
Simple..and has merit. No radials
to mess with. Simple relay switching system.
## http://myantennas.com/wp/product/cmc-230-5k/ As you can see from the
graphs,
he attains 8200 ohms Z..and 8000 ohms RS on 40m.... with just 4 x cores ( 2.4
OD, type 31)
and teflon coax. ( 8.5 k Z + 8K RS on 80m). If you use a fan type dipole,
sorta stagger tuned perhaps,
you should be able to achieve low swr. Id suggest keeping the top ends away
from the tower if at all possible.
Another possible option is to use larger gauge wire, like at least 10 ga..and
possibly 8 ga.
Either will result in a flatter swr curve on 80 /40m.
## You should be able to do 5 x CM chokes with no more than 20 x cores. If
you optimize the
CMs for just 40m, you should be able to get the Z + RS even higher.
## danny is currently experimenting with the larger .280 inch OD ( 14.5 gauge
center conductor)
teflon coax. Its slightly bigger than the .249 inch OD of RG-8X. The typ
RG-303 /RG-400 coax
uses a 18 ga center conductor. RG-393 uses a 13 ga center conductor.... but
is aprx .392 inch OD.
## This new coax hes playing with is mid way between the overkill RG-393..and
the smaller RG-303 /400.
Since its not much bigger OD than 8X, it should be able to be wound on type
31 cores....and the peak V
rating is quire a bit more than 303/400...... but no where near what 393 is
rated for. A 100 kv hi pot tester
wont put a dent on 393 teflon coax..provided the dual silver plated braids are
back from the ends. If you can keep
the swr down, that alone will solve most of ur peak V issues.
Jim VE7RF
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