Some Technical and Non-Technical Notes On The
Slinky Antenna
A
Slinky is a toy and a science class tool made from a flexible 90 turn
spring coil with a diameter of 2 3/4 inches. Each Slinky coil contains
approximately 67 feet of spring steel wire and weighs about ½ pound.
When a Slinky is compressed, it is only 2 3/4” long, but it can be
stretched into a helix as long as 15 feet in length without becoming
deformed .
An
antenna made from Slinky coils -is light weight and simple to put up and
if need be out of sight.
Slinky
type antennas are great for improved broadcast. and, short-wave
listening. Another use is for ham radio transmitting in a limited space
environment or outdoors where the antenna can be many times smaller than
a regular dipole, long wire, inverted v or vertical antenna.
Slinky
antennas can be made to cover any frequency range in the medium and
short-wave bands for receiving or transmitting.
While
we have been experimentation with slinky coils as antennas since the
1960's, we love to play with them and seem to discover something new
every time we put one up or adjust the ones we have up. No doubt there
is still much to be discovered!
A
standard (original) Slinky coil is a quarter wave between 7 and 8
megahertz when stretched out to only 5 to 15 feet.
To
tune the Slinky within that range, all you have to do is extend the coil
to approximate size then expand -or -contract it to reach the desired
resonance.
Close
to 7-1/2 feet, a Slinky is a quarter wavelength at the upper end of the
40 meter ham, therefore a dipole antenna for 40 meters can be easily
made from a pair of original Slinky's with pretty good transmission and
reception results.
Many
people use our Single and Double Short-wave Slinky antennas to fit the
small area inside an apartment, on a balcony or deck and even in a hotel
room because they can be put up or taken down in a couple of minutes and
can be transported in something as simple as a suitcase or plastic
grocery bag or just carry it in your hand.
Ham
Radio Dipoles above the 40 meter band can easily be made by simply using
an antenna tuner which almost all hams own, but can also be easily made
by simply shorting out some of the coils on the outer end of each
Slinky. The length and number of coils to use depends on the height
above ground and surrounding buildings, gutters, TV antennas and other
large man made objects.
Another way to change the frequency is to hang a different length wire
pigtail with an alligator clip on one end to the outer ends of the
Slinky coils and just let them hang down and blow in the breeze.
This
is especially easy for making an 75-80 dipole out of a 40 meter Slinky
Dipole when you don't have an antenna tuner handy.
By
adding another original Slinky coil to each end of the 40 meter dipole,
and stretching the whole antenna to about 30 feet in length, you can
make an 80 meter dipole that will fit in most attics and family rooms
and even a basement ceiling or hallway.
Our
Single Slinky and Junior Slinky antennas work extremely well for
short-wave reception from.5 to 30 mhz, but you can get even better
reception with a double Slinky antenna if you're really interested in
short-wave listening and also listening to the HF Ham Bands.
The 2
Slinky doublet antennas have a resonant peak around 5 to 11 mhz and also
around 16 to 24 mhz which covers most short-wave broadcast frequencies
and the HF ham bands, but do quite well on all the other frequencies
between .5 and 30 mhz too!
I use
my 2-80 ham dipoles at 35 feet for my HF and 6 and 2 meter ham radio
transceivers, and for short-wave and scanner listening too.
When
I checked both my 2-80 dipoles with an MFJ-259B antenna analyzer they
both had an SWR less than 1.5:1 from 50 mhz all the way to 180 mhz.
When
using the antennas alone or with an antenna tuner, any given frequency
will be resonant in two different stretches of the antenna, but the
antenna will always be more efficient with the longer length.
You
will notice that receive signal strengths will be about the same no
matter how far you stretch out the Slinkies, but there should be a
slight increase when they are both stretched out to around 15 feet each.
The resonant frequency range will also be wider at longer lengths.
The
single can be stretched out at any angle that fits your space at the
given location and moment. You can tie a string to one end and tie the
other end to a tree, post, fence, gutter, downspout, or even a 10 ft
piece of 1” PVC slid down into a chain link fence post like I've done.
The
dipole or doublet can be used in almost any configuration too. It can be
used as a sloper, a vertical, a dipole, and inverted v, a flat top or
any combination of these configurations.
Most
people don't think about using our Slinky Antennas as anything but a
simple dipole, but they work equally well as a vertical with the hot
side going vertical and the ground side laying on the floor or ground
and an inverted v with the center insulator suspended and the two
Slinkies coming down at 45 or almost any other angle you can stretch
them to fit.
The
2-80 can also be used inside with the center insulator in a corner and
the Slinkies strung along the ceiling wall junction or down to the wall
floor junction in the corners of the room.
In
all instances, a small diameter Dacron or polyester rope or even weed
eater line should be strung through the center of the entire antenna for
support and to keep the heavier center from sagging.
Indoor Installation of the Slinky Ham Radio Dipole Antennas
No
indoor antenna is ever going to work as well as the same antenna mounted
outdoors! This is due to the antenna being inside the office, house,
camper, garage, apartment, condo, etc.
Inside you are usually surrounded by gutters, heating ducts and
electrical wire, central air and are usually sitting on top of a furnace
that has hundreds of feet or metal ductwork running in all directions
below (and/or above) you.
BUT,
indoor antennas do have the advantage of being out of sight of your
neighbors, wife and children and they are very easy to adjust or change
when the weather or height would not allow you to do so if it were
outside.
In
many areas of our ONCE FREE COUNTRY antennas aren't allowed at all even
though you may have paid a fortune for the land your home is built on.
Your neighbors control your radio hobby as much as they can get away
with it.
Indoor suggestions;
A
simple eye hook or one of the cup hanger hooks mounted under the shelves
in your old kitchen cabinets can be screwed into the top corner of the
wood molding around a window or door and the antenna strung between
these hooks.
If
you have a corner window, it's really easy top use it as the mounting
place for the center insulator. You can then run one side of the dipole
to the corner to the left and the other to the corner to the right of
that window, or to a closet door, or to a plant hanging hook screwed
into the ceiling at any point that fits your situation.
You
can also run the legs of the dipole down to the floor of each corner and
place a hook there with a string or weed eater line as a stand off
insulator.
One of
the best places to put any antenna indoors is in your attic. There are
usually no walls at all up there and you can run your antennas all over
the place with nothing to get in your way or the incoming radio signal's
way.
Another
way to mount your antenna indoors is to run the coax up a corner and
bring one leg of the dipole back down the same corner and the other leg
to a top corner. That's less noticeable than the inverted v.
Under The Soffets
Your
Slinky Dipole or short-wave antenna can be easily hidden by putting
hooks into the soffets at the corners of the house and tying the antenna
to the hooks with a long piece of heavy fishing line or weed eater line
strung through the entire antenna and it's center insulator.
Outdoors
You can
do anything you want to outdoors, after all you're a licensed ham radio
operator and you took a test to get your license (We Hope) and you've
probably done this so many times before it's old hat!
Just experiment and have fun and be sure to stay clear of all
power lines!
FROM ONE OF THE ORIGINAL 1966
INSTRUCTION SHEETS
Note; ALWAYS
RUN A PIECE OF ROPE THROUGH THE ENTIRE ANTENNA AND DO NOT TO LET THEM
GET TANGLED UP! STRETCH TOO FAR-THEY'LL LOSE THEIR SPRING!
The Slinky
Dipole
Even if
you're going to stretch it out tight or close to it, you should run a
rope inside the coils. Each of these antennas works better at different
lengths according to their height above ground and that usually takes a
little experimenting at your location. Even with my 2-40 dipole in the
attic, I run string through the entire antenna so that I can adjust it
in both length and spacing. My vertical in the shack has nylon string
through it too. It lets me adjust the height by simply looping string
around any loop of the Slinky. I can make the top half close spaced and
the bottom half wide spaced. I have one Slinky stretched from the top of
a windowsill over to the old entertainment center, which houses my
radios etc. I have another 2-160 in the attic stretched 66 feet from one
end of the house to the other. It has nylon string running all the way
through it.
You can
also hang any of these antennas as inverted v's in a very small space! I
also made an 80 meter vertical (25 feet long) out of one 67 foot Slinky
by throwing a weighted string over a tree limb and pulling up one end of
the Slinky with another string tied to the bottom end and letting it
hang down and tying it off before it touched the ground. I used another
Slinky as a ground radial at the bottom stretched out only 5 feet and
attached each one to the coax ends.
The
possibilities are endless it seems, and I wake up in the middle of the
night very often with more ideas, but there's not enough time in the day
to try them all so far. I'm hoping all of you will try new things and
get back to me on what you've done.
If
you're going to use the original steel Slinky and the Black Oxide Coated
Slinky antennas outside for any extended length of time, we suggest you
get a 97¢ can of clear spray paint from Wal-Mart, stretch the antenna
out to about 10 feet, and put a couple of coats of paint on the coils.
After all, they're made from steel and will rust over time if not
protected from the elements.
The
antennas made from Solid Brass Antennas, 24K gold plated Brass ones and
the powder ones do not need to be painted.
Below
is what we found in our own installations. Your results may vary due to
height and surroundings
Model 280 2
Slinky's--With 84 ft of RG8X coax and the slinky coils stretched to 15
ft each,
I can easily tune mine to a very
good SWR:
6 meter band (50
MHz): better than 1:1.2 over entire band, except up to 1.6 around 50.500
MHz
10 meter band
(28 MHz): 1:1 over entire band
12 meter band
(24 MHz): 1:1.2 over entire band
15 meter band
(21 MHz): 1:2 at the low end, to 1:1.5 at the high end of the band
17 meter band
(18 MHz): 1:1 over entire band
20 meter band
(14 MHz): 1:1.5 at band limits, 1:1 up to 100 kHz from band limits
30 meter band
(10 MHz)): 1:1.1 at the low end, to 1:1.4 at the high end of the band
40 meter band (7
MHz): 1:1.5 at band limits, 1:1 up to 30 kHz from band limits
80 meter band
(3.5 MHz): 1:1 over entire band
160 meter band
(1.8 MHz): will not tune ON THE 2-40 AND 2-80, you need the double
2-160!
160 4 Slinky
model WHICH TUNES 2 THRU 160 WITH ANY GOOD ANTENNA TUNER.
CAUTION! ALWAYS STAY CLEAR OF ALL ELECTRICAL POWER LINES
Installation,
height and surrounding objects are different for every user. Some users
don't need a tuner and some do!
Slinkys
for shortwave antennas -