[TowerTalk] 4 square for 80

[Jim Thomson]

Date: Mon, 26 Sep 2016 08:35:15 -0600
From: Steve London <n2icarrl at gmail.com>
To: towertalk at 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