Thanks for all the great info. I will have my L in the air soon and hope to
meet you on top band!
Ron W8VZM
On Thu, Jul 1, 2010 at 12:55 PM, Charles Moizeau <w2sh@msn.com> wrote:
>
>
> > Date: Wed, 30 Jun 2010 19:42:01 -0400
> > From: w8vzmron@gmail.com
> > To: topband@contesting.com
> > Subject: Topband: Inverted L?
> >
> > Hello all!
> > At my new QTH I finally have room for 160m antennas and a rig that has
> 160m
> > at the same time! I have a number of tall trees and am thinking of using
> one
> > as a support for the vertical part of the inverted L. Of course it would
> > need to be away from the trunk as much as possible, I think I can manage
> 6
> > feet or so out and 50-60 ft up. Plenty of other trees for the end
> support.
> > Location of the tree is good for radials so that will not be a problem. I
> am
> > thinking remotely operated cap for tuning. Not sure of the value needed.
> I
> > figure this will be better than my 204' G5RV inv. vee @ 55'. I also have
> > plans for beverage rx antenna(s).
> >
> > Questions
> >
> > 1. What am I forgetting?
> >
> > 2. Value for variable cap?
> >
> > 3. Wire size / type?
> >
> >
> >
> > --
> > Ron W8VZM
> >
> >
> >
> > I have sworn upon the altar of God, eternal hostility against every form
> of
> > tyranny over the mind of man.
> >
> > Thomas Jefferson
>
> ***************************************
>
> Ron,
>
>
>
> I have a situation similar to yours.
>
>
>
> At the edge of the lawn area in front of my house is an ash tree from which
> I have hung the “elbow” of my inverted L. I chose a limb that stuck out
> over the lawn such that the perfectly vertical leg is spaced about 10 feet
> away from the tree trunk.
>
>
>
> It was an easy bow-and-arrow shot to establish the elbow support location.
> I use 3/16-inch line from SyntheticTextiles to suspend the elbow and add
> about eight feet of 3/8-inch air compressor hose to sleeve the support line
> so that the line won’t chafe where it crosses the limb.
>
>
>
> I’ve had this simple mechanical suspension in place for a couple of years.
> The bottom of the vertical leg terminates in an alligator clip, and that
> joins the matching component. When the wind blows hard, the limb sways
> and the alligator clip pulls free of its terminal.
>
>
>
> It is on my to-do list to have a Kevlar-cored antenna support line, sleeved
> with hose, pass over the limb and attach to the eye of an appropriate pulley
> (available from Lowes, but not Home Depot). Then a proper halyard (3/16”
> Syn-Tex) would pass through the pulley’s sheave and be anchored at ground
> level through some black rubber bungee cords or alternatively another pulley
> and a counterweight.
>
>
>
> The fact that I’ve been lazy bespeaks the quite satisfactory arrangement
> that I’ve been content to live with for a couple of years.
>
>
>
> And now for the electricals. I use 12-gauge, solid copper house wire
> (available more advantageously from Home Depot than from Lowes). My total
> run is 170 feet, with the vertical and horizontal legs each 85 feet. Why
> these dimensions? I assumed a quarter wavelength of this wire to be 128
> feet. I wanted the current maximum to occur at the midpoint of the
> vertical leg. Why? Given the sinusoidal current distribution, having the
> current maximum at the half-way point will maximize the total current
> appearing in the vertical leg. Since a current maximum occurs a quarter
> wavelength back from an antenna’s end(-s), you do the arithmetic and you
> will see why I have 85’ up and 85’ out.
>
>
>
> Your height capability is different, so your leg lengths would differ from
> mine if you follow my scheme.
>
>
>
> I also wanted to minimize losses from the impedance matching device at the
> base. With a total antenna length of about 1/3 wavelength, the feedpoint
> impedance is inductive and all I need is a capacitor in series with the
> coax’s center conductor. NO INDUCTORS! I set the capacitor for minimal
> SWR at 1.810 mHz. It’s set-and-forget for 160m. (For operation on other
> bands, I run the feedline through an antenna tuner in the shack).
>
>
>
> Ground radials are important. I use #12 and #14 house wire, but it works
> out a bit cheaper to purchase 12-2 and 14-2 spools, strip off the outer
> jacket and plant the two insulated wires and the ground wire.
>
>
>
> I did 8, then 14, then 22 radials an inch or so deep in the lawn area. Radial
> length varied from 120 to 60 feet. After adjusting the variable
> capacitor, my best-achieved SWR went from 1.6, to 1.3, to 1.2.
>
>
>
> This spring, I’ve added, with significantly more labor, 16 more radials
> that are all about 160 feet in length, but, importantly, these 16 run into
> the woods. Alas, my SWR readings and bandwidth seem hardly changed. Yes,
> I’ve encountered the usual “law of diminishing returns”, but I have the
> nagging fear that the trees are “eating” my rf and therefore those 16
> radials aren’t gathering any of it to return the current to the antenna base
> for “recycling”.
>
>
>
> Watch this space for results of my experiments disconnecting ALL the
> radials, and then reconnecting just the lawn or just the woods radials.
>
>
>
> Apprehensively 73,
>
>
> Charles, W2SH
>
>
--
Ron
I have sworn upon the altar of God, eternal hostility against every form of
tyranny over the mind of man.
Thomas Jefferson
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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