[TowerTalk] 80 Meter yagi question

[Jim Thomson]

Date: Mon, 9 Oct 2017 10:17:37 -0700
From: Jim Brown <jim at audiosystemsgroup.com>
To: towertalk at contesting.com
Subject: Re: [TowerTalk] 80 Meter yagi question
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<2f079a2a-ae46-4d37-3abd-c42602de55aa at audiosystemsgroup.com>
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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