[TowerTalk] (no subject)
Wed, 13 Sep 2000 18:43:58 EDT
<< In a message dated 9/11/00 5:26:32 AM Pacific Daylight Time, K7GCO writes:
Date sent: Sun, 10 Sep 2000 15:58:22 EDT
Subject: [TowerTalk] 80-75M Inverted Vee or Dipole
> Let me drag you all kicking a screaming back to the last Century.
> 1.) Cut an Inverted vee or dipole (no bow tie needed) for 1/2 WL at 3.6
> MHz. 2.) Connect 136' of open wire line (121.6' 450 ladded line). This
> really works great on 160M also but the feedline is twice as long.
I assume on 160 the dipole length is doubled also?
> 3.) Short out feedline and grid dip to 3.6 MHz.
By trimming the feedline?
> 4.) Connect one feedline wire to center of coax switch or directly to
> 5.) Connect other feedline wire to stator of BC 3 gang variable all tied
6.) Connect rotor frame to coax switch or rig ground.
How do you make the antenna go below 3.6 MHz (poor grammer), with only a
series capacitor, if the antenna and feedline is resonant on 3.6? (it's
"RF Fudging!" and it takes practice).
I understand how a series capacitor will cancel inductive reactance
as frequency is increased, but how does it cancel capacitive
reactance when you move below 3.6?
73, Tom W8JI
Tom: You are either kidding or are lacking in the most elementary of
antenna fundamentals or experience.
Yes the dipole is twice as long on 160M and perhaps I should have laid it
out crystal clear for everyone but you are the only one that is never sure of
what to do. I was trying to emphasize that 272' of feedline for 160M can be
hard to handle in a normal lot when it has to be run around the yard but I
have done that. I'll have 6 acres in SD and will have open wire line running
all over the place (10' off the ground for safety purposes of course). I use
coax also. Mostly 100 ohm balanced (2-50 ohm equal length coaxes series
connected--shields only) for dipoles, horizontal quad loops, beams etc.
When one shorts out a resonant 1/2 WL length feedline connected to a
dipole, grid dips and finds the resonant frequency other than 3.6 MHz, you
can add or subtract to either the feedline or antenna. It's based on a Basic
Law of Reactance and Feedline Lengths. You either "give away or take away"
(add or subtract) in a manner that "creates the desired results" and can be
done without great knowledge of theory--who gives a damn. Too much
"personally massaged theory" is thrown around here all the time. Everyone
has their version. I haven't even found a new Appliance Ham that couldn't
get the hang of this simple resonant frequency adjustment problem with a
little instruction. Consult some of those books you keep referring to in
One of the design concepts I incorporated into this antenna concept for
simplicity is this. If resonant at 3.6 MHz, the bandwidth is S O W I D E
that you may not even want to try and lower the SWR at 3.5 MHz with which in
this case as I'm sure you almost suggested--an inductor, a longer feedline or
antenna. With 1:1 at 3.6 MHz (it was 1:1 with coax also) I saw no need to
lengthen either when it's 1.2:1 SWR at 3.503 MHz. (Note I'm 3 kHz inside).
It's called "Proper Application and Placement of the SWR Curve 101" on the
low side to get minimum SWR on the high side. As one operates higher in
frequency above 3.6 MHz, a low SWR can be obtained all the way to 3.997 kHz
and higher within the range of the BC 3 gang variable Xc (capacitor) with a
single wire dipole and no Bow Tie construction is needed. I did use 5 wire
cage dipoles however, before I came up with this idea 60 years ago. These
variables came out of AM Broadcast Radios and had 365 uufd/section and can
still be found in flea markets real cheap. That's particularly handy with
the 50 ohm output rigs as you just adjust the variable Xc for max output.
The height of a dipole or angle of an inverted vee can be adjusted to 50
ohms. A half wave of feedline repeats this 50 ohms to and at the end of the
feedline ragardless of it's Zo. The open wire feedline used had a 12:1 SWR
but didn't really care. Guess it's Zo. This is the lowest loss feed system
in Ham radio that tunes the whole 80M band. 160M also with BOTH components
I do this in mobile also with a BC variable in series (inside the car in a
box) right at and in series with the feedpoint at the top of my Porsche. I
actually cut a hole in it. I can get 100 kHz of SWR less than 1.5:1 at 75M
and 160M MOBILE. Remember: Resonate low (in the band) and operate high.
Many have mastered it without further instructions. One ham at a convention
talked to me about it for 10 minutes how well it worked. I suggested he buy
me lunch so I could keep my attention and he did. 10 minutes is about all I
can take without food. I also suggested he use the Automatic Resonating (No
Touch) system Don Johnson has. I hope to have plenty of time when I run into
him again near a restaurant. I should record some of these performance
testimonials and play it to the TT Nay Sayers.
In line with the desire to keep Post short as possible, I usually leave
out the most elementary of concepts but unfortunately have to frequently
explain them to you.... Don't complain if I make my Posts a bit longer from
now on as my spare time is needed to explain new ideas to others. Those who
follow my instructions usually by sheer creative imagination and high
intellect figure out the rest which is the desired goal. It's designed to be
a "learning experience" like many of us used to developed our tune up skills.
After class instruction can be arranged for "calculating antenna lengths,
trimming feedlines or optimum application of SWR curves" if needed. I am
always glad to help everyone learning to use better and simpler techniques in
the never ending technical challenge of transferring the RF from "F-F"--Final
to Feedpoint. I use conventional antenna tuners only when I have to. With
link coupling (before Art Collins) we didn't need external complex expensive
automatic unbalanced only tuners with about the same range with balanced or
unbalanced feedline loads of up to 1000 ohms (2-8 turn link and one variable
Xc.) You are being ripped off. That looks like "RF Black Magic" today to
some who have never used anything but coax and 50 ohm output no-dip finals.
It's like those who grew up after TV. They don't know what it was like
before TV. We actually watched the radio and created visual images from the
great Radio Writing of the "Detective Mystery Thrillers." When I hear them
replayed I can usually remember what was going to happen as the images were
so vividly created.
We need more open minded attitudes for better ways to do things with shorter
delays. Just think what Ham Radio would be without Sideband. I however will
be on AM again with a Art Collins KW-1 and heavy audio. I may change it to
Link Coupling--I'm just kidding. Mine was given to me by an appreaciative
manufacturer for technical tips and I hear they are selling for Big Bucks.
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Administrative requests: towertalk-REQUEST@contesting.com