Date: Mon, 26 Sep 2016 08:35:15 -0600
From: Steve London <n2icarrl@gmail.com>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] 4 square for 80
K2AV writes:
>Diversion of power to miscellaneous conductor paths is almost universally
lossy and never in directions and modes desired in our attempts at
directional arrays.
>The common mode path on the outside of coax shields is lossy first because
it has a thick jacket which is never designed for low loss, second because
it often lays on the ground or is buried, a very lossy situation. Try your
20 meter dipole laying on the ground to check that out if you're not
convinced. And if that is not enough, coax is often taped to towers, making
it a transformer winding to the metal of the tower, whose reradiation is
certainly not going to be useful in a 4 square.
---------------------
Okay, let's put in those K9YC multiturn chokes at each feedpoint. This
provides a -resistive- load to the common mode path. In fact, these
chokes can get pretty warm. So, the way I see it, putting in common mode
chokes does nothing to reduce the system power loss that K2AV is so
concerned about.
73,
Steve, N2IC
## The feedlines have to be an electrical 1/4 wave. You cant do that with a
K9YC
multi turn CM choke. They barely reach as is. Plan B, if you have to use
multi turn chokes,
is to use electrical 3/4 wave long lines, but then the swr BW will decrease
by a bunch.
## If the multi turn K9YC CM chokes run hot, they are not wound, nor
constructed correctly.
For 80m mono band use, its pretty easy to achieve 8000-16,000+ ohm Z...with
most of that
being resistive. 2-4 x CM chokes are used in series. But electrical 3/4
wave lines would be required.
## RG-303 teflon coax will handle plenty of power, with its 18 gauge center
conductor encased by the
teflon. RG-304 teflon coax is a hair bigger OD than 8X, and uses a 14.5
gauge center conductor.
304 will handle stupid amounts of power, esp on the low bands. 303 /304 is a
lot easier to work with than
RG-393 teflon coax, with its .390 inch OD and 13 gauge center conductor.
## The strings of beads that dx eng sells for their 160-6m vertical arrays
looks to be only abt 2 foot long,
with 100 x small beads on small coax. 2 foot of the large beads, slid over
213U is barely 980 ohms on 80m,
and is not long enough to work worth a damn on 160m. If beads are to be used,
you require a helluva lot of em
on 160 or 80m. You can look up the Z per bead, then total the beads
required. Even with several feet of beads,
the problem is the CM bead choke is inductive. But at least electrical 1/4
wave lines could be used.
## On RX, the noise on either a 160m or 80m 4 square is going to be pretty
wicked. Depending on the application,
a dedicated RX antenna would be required to supplement the 4 sq.
Jim VE7RF
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