Date: Mon, 9 Oct 2017 10:17:37 -0700
From: Jim Brown <jim@audiosystemsgroup.com>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] 80 Meter yagi question
Message-ID:
<2f079a2a-ae46-4d37-3abd-c42602de55aa@audiosystemsgroup.com>
Content-Type: text/plain; charset=utf-8; format=flowed
On 10/8/2017 12:18 PM, john nistico wrote:
> I am thinking of adding a rotatable 80 meter YAGI on one tower. Any
> suggestions?
<Hi John,
<As the first part of your thinking about this, I strongly suggest that
<you study my applications note on this topic. The most important
<conclusion is that height of a horizontally polarized antenna is VERY
<important on 80M. Figuring out a way to get a simple dipole (or pair of
<dipoles) HIGHER is about as effective as a two-element Yagi. I've had
<great success with two dipoles up 130 ft or so at right angles to each
<other. The same physics applies whether the antennas are full size or
<loaded.
<http://k9yc.com/AntennaPlanning.pdf
<73, Jim K9YC
## He did not say how high the proposed 80m YAGI is. Steve, VE6WZ
had his hb 2 el 80m yagi up 100 feet... on a 50 foot wide postage sized city
lot.
Used 66 ft long eles on 80m, with hb center loaded cu tubing coils.
The only place he could install the UST HDX-589 tower was next to his deck..
which put it exactly 14 ft away from his property line. So he made the boom
28 ft long.
He also interlaced his 2 els on 40m..on the same boom. He is working EU on
SSB
like a machine gun, late at night.... their sun rise. He has NO trees
anywhere. That array of his
is extremely effective, FB is superb across the band. Box at both feedpoints is
more .25 inch cu
tubing coils and vac relay switched for cw + ssb.
## A local fellow, aprx 30 miles north of me, has 2 x dipoles on 80m, at right
angles..and both
up 110 feet. But he is on acerage, and has loads of 120 ft tall douglas fir
trees. He shot a line over
4 of em..and the rest is history. Very effective array on 80m.
## One big advantage of dipoles and yagis is they are quiet on RX. You
require one heck of a lot of
real estate for either a single vertical or a 4 square. Sure they work good
on TX.... but they also require
a dedicated RX ant array..and thats where the issue starts up. Tough to get
the dedicated RX ants away from the
TX verts. That or the TX verts have to be de-tuned on RX..pita.
## You dont hear of many 40m 4 square arrays these days. A simple 2 el
rotary yagi at a reasonable height,
like 70 ft or higher, will typ trounce the 40m 4 square.
## regarding the infamous seco systems Tornado drive, if you buy one of these
superb devices, order it
with the plastic coated, .25 inch OD copper tubing coils.... vs the plastic
coated .25 inch OD aluminum tubing coils.
A single 12 vdc motor simultaneously expands or compresses BOTH coils.
He can build them to any uh range you desire.
But the caveat is.... they have a 2:1 max to min uh range. Mine are 6.25 uh
to 12.50 uh. He can build smaller ranges than
this, and also a lot bigger ranges. He can also build a SINGLE
compressible / expandable coil.... like for the base of a vert.
## Aluminum only conducts 60% as good as copper. .25 inch OD copper =
.417 inch OD aluminum.
The tornado drives are controlled with a screw driver controller. MFJ and also
Ameritron makes the controller.
Both are identical, except for the name on them. The Ameritron version is
called a SDC-102. It comes with a digital
readout turns counter..and also 10 x pre – sets. Also comes with manual up /
down controls. Just bring up the closest
pre-set, then manually tune up /down for flat swr from 3500-4000 khz.
## Since I have 2 x digital LCR meters, I wired one meter to coil # 1....
and the 2nd meter to coil #2. Then varied the uh
from min to max. They both tracked identically from min to max uh. Zero
issue with the compressible coils, since there is
NO sliding contacts or wheels like on a roller inductor. And no, you cant
blow em up with serious QRO either. All that is required
is a tubing type helical hair pin.. + a heavy duty CM choke.
Jim VE7RF
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|