A Remote tuned Dipole that covers ALL of 75/80 Meters
without a tuner!
Now one dipole for the
entire spectrum from 3.5Mhz - 4.0Mhz!
Designed, built and tested by
W4QJP & KC4TAQ
(See latest update info at end of this
Editors note: This project looks
very complicated but it is not!
The principle behind this remotely
tuned dipole that makes it work so well is that the overall length of
the single dipole can be shortened or lengthened as needed for lowest swr
and resonance on the entire 75/80 meter
band with just the flip of a switch!
Although the drawings and plans
below represent a field tested and working system by the designers, this
should be considered as an experimental project.
It is such a simple
idea, that turns out to work great..why did'nt I think of
Now you can have the
entire 75/80 meter band at your disposal using one
without the use of a
How it works and is assembled:
HOW IT WORKS: version 1- refer to drawing
The wench at the bottom of the tower is
used to take up or let out the Dacron rope that is routed up the tower and
connected to a pair of Dacron ropes that pass through two pulleys near the
apex of the antenna. Each rope is connected to the ends of the antenna
wires which in turn are routed between a pair of sheaves to keep the wires
close together and maintain electrical contact.
The wires continue
down to the lower sheave or pulley, around and back through the upper pair
and up to the feed point insulator where they are connected directly to
the center and shield of the coax, the same as you would with a regular
inverted V or dipole. The lower end of the take-up system is attached to
Dacron ropes that pass through elevated pulleys and are then attached to
The weights maintain tension on the wires as the
wench lets it out or takes it up.
After the antenna was installed,
an MFJ analyzer was used to find the lowest reflected power at regular
intervals on the 80 meter band and the Dacron rope was marked with
frequency tags at the wench. We can take up or let out the wench until
we’re at the frequency desired.
This would be the budget
version of the adjustable inverted V. You would do the frequency changes
by cranking the wench handle at the base of the tower – maybe not so good
on a rainy day.
If you desire to operate the antenna from within the
shack, there are several methods that may be employed.
version would use pulleys to route the Dacron rope into the shack where
you can directly control the wench and see the frequency
A counter could also be driven from the wench
although a tracking system is unnecessary if you tune to the lowest SWR at
the frequency desired.
We added a 12 volt DC window motor
to drive the wench and control it with a DPDT switch which takes its power
from the same source that powers the radios.
You can imagine a remote
control system to track the position, run the wench and limit travel, but
the cost goes up. One possible solution that could be added to the 12 volt
system, would be a wired or wireless camera positioned where it can see
the wench and tracking system and connected to a PC or small monitor in
the shack. Our prototype antenna goes from around 3.40 Megs to well about
4.4 Megs with the push of a button. We now believe the concept is sound.
We believe the same system will work on 160 meters or any band where a
single frequency antenna won’t cover the entire band. As always,
feedback is welcome.
Additional notes, suggestions and comments:
coax feed comes up between the two pieces of Plexiglas and is held in
place on one side only with zip ties. The ¼ 20 SS bolts are inserted
through the “bottom”. The 2 sheaves are dropped onto the bolts
and the soldering is done before the “top” side is installed.
“rules” are the same as for any inverted V. Nothing we’ve done has changed
the operational characteristics of a “standard V”, as far as we can tell.
What did change was the ability to find the best apex angle as it is now
just a matter of tuning to any given frequency and looking at the data,
then raising or lowering the antenna and comparing to fine the best center
height relative to end heights.
Sam, KC4TAQ, the
co-designer - lowered the tower from 55 feet (and antenna) to around
35 feet but made no changes to the end heights and found it moved the
resonant frequency well down the band. All he had to do was take up on the
wench (from in the shack) and it came back down to a 1 to 1 SWR. It does
not appear that height is critical to this design.
We are using a
DC window motor direct driving a wench spool with Dacron rope to do the
adjusting. Due to the distance from the top block to the wench, the Dacron
level winds perfectly onto the spool. As an alternative, you could use a
small boat trailer wench or you may even find a large bait casting reel in
a flea market if you want to change frequencies at the base of the tower.
In this case, some means of tracking the frequency change will be needed.
One option would be colored heat shrink tubing placed at proper intervals
along the Dacron rope to create a visual scale.
When tuning from in
the shack, we just use low power on the desired frequency and run the
wench until the SWR falls to a minimum. Our objective was to design an
antenna that would allow you to go to the local super center and find most
of the parts you need.
As you see in the documentation, the critical thing is to keep the returning wire as close as
possible to the top wire. Stiffer wire may work, but it hardens
quicker than the flexible stuff but you should get several years of
service even with #16 or 14 stranded copper.
The weight strips are
to keep the blocks from flipping over. We didn’t want any extra metal in
close proximity to the wire, hence the Plexiglas extension.
weight (lead sinkers) can be added to the bottom of the Plexiglas strips
Theoretically, there should be no reason why you
could not use this concept to go from 160 up to 40 meters or higher. It
would require a multi-part pulley system at the turnaround block if you
take up more than half of the wire in the system. A 40 meter trap may also
allow for two bands. If you use a larger diameter wire from the feed point
out to the trap then you should be able to cover the 40 meter band without
The counter weights need only keep a reasonable amount of
tension on the wires. We used about 12” of 3” PCV pipe with a cap on the
bottom and have it about half full of steel punch outs from one of our
iron workers. Sand bags would work equally well. We would like to hear
from anyone that decides to build this antenna.
Designed, built and tested
by W4QJP & KC4TAQ.
Simple principle of operation!
In the drawing above, when the wench is
activated, it either pulls or releases the tension on the counter
weights thru a system of pulleys at the apex and on the end of the
antenna on both sides equally depending on
whether you want to lengthen or shorten the two sides of the dipole. This
is done using one rope connected about half way up from the wench where it
connects to the two "control" ropes leading eventually to the end of each
half of the dipole. By activating the wench, the total length of each half
of the dipole is changed.
You simply watch your swr
meter for the lowest swr on the frequency your tuning to!
reach that "sweat spot"...you stop! Your done!
Editors note: The designers report that about 6 adjustable
feet on each half of the dipole is required for complete band coverage.
(Longer on bottom end of the band, shorter on the top end.) Your total
length results may be different due to your height above ground so some
experimentation may be needed. But, once you get the correct total length
for lowest swr over all portions of the band when remotely tuning the
antenna, no more experimental length changing is
The key and most important parts of the
system is the pulley mechanisms and the very flexible wire used as
shown in the drawing below.
The end wire
separation MUST be touching or kept at a minimum all the times.
long as the "loop back" section is kept close to the upper wire, it
becomes essentially "invisible" to the overall length of the main
It is as simple as
Blue line is
cord leading to counter weight. Upper left hand cord (not
shown) leading to apex pulls
is left out of drawing for
clarity! (only one side of lower part of antenna
Notice extra weight
bar made from Plexiglass in lower right in drawing. This is used to help
keep the pulley from "flipping over" by adding the appropriate weight
hanging down from it.
Download a Pdf file
of this project here!
If there is
enough demand, we may offer, in the future,
a kit of parts that
may be difficult for some builders to fabricate or find
Your feedback is appreciated!
Lookup email address on QRZ.COM for W4QJP
from George, W4QJP
"Hi guys, I've put together a small web
site for a
proposed loop tuning system Sam and I have been talking about for
a couple of years.
It's based on the same principal we're now using on
the RTV 80 (inverted V). We expect to give it a try in a few
I'll let you know how it works or check in to the
website as we'll update it as we go along."
George W4QJP (Editor note...make
sure you see the entire web site below. Especially the "How it Works"
section...very cool idea and nice "animated" graphics.