Herb: Below you will find what I saved from discussions the last time
this question was raised. -- Fred K1VR
From: km1h@juno.com (km1h @ juno.com)
To: <topband@contesting.com>
Date: Thu, 31 Jul 1997
Subject: km1h: Re: TopBand: Slinky Beverage
As the originator of the Slinky Beverage some 10 years ago I will say it
works very well indeed. It may not equal a 2 wave wire version on 160
but
it does very well in a limited space.
There were many discussions here last year on the subject . One person
went to great lengths to explain why it was no good. As you have noted,
others have tried it and like them. I view it as a helically wound slow
wave antenna. Since helically wound antennas have been used for
everything from mobile whips to 40M beams I find no reason to doubt
their
use here.
My own system uses 5 large diameter ones in series and stretched over
175' At the far end I terminate with a 500 Ohm resistor and run 3 135'
radials, one directly in front and the other 2 roughly 10 degrees either
side. The terminating xfmr is the familiar 9:1 balun. For me the Slinky
has a better S/N ratio than a 1 wave wire used for comparison. The f/b
exceeds 25dB. Signal levels are so good I rarely use a preamp and when
I
do the gain is set at 10dB or less. I had no trouble hearing the VK0,
FR,
ZS8, or anything else this past season.
I have not taken any impedence measurements or tried to get into some
theoretical funk over it. For me, they work fine 160 thru 30M. Neither
have I used more or less Slinkys or stretched over different lengths. I
just used what fit my property requirements. I would really like to here
from others that have experimented.
There were several posts to the reflector today that got my interest up
again. I just might do that test with a FS meter and try to determine
reasonance and the PROPER terminating resistance. The other comment
about
galvanized wire also was intriguing since the Slinky is Cadmium plated
steel. Time to buy a can off Deep Woods Off and go play again!
Carl KM1H Only 262 DXCC on TopBand and 311 on 80
=====
From: W8JITom@aol.com
Subject: TopBand: Slinkys impedance
In a message dated 97-01-09, you write:
>3. I use 5 of them here and stretch them a total of 175'. At the far end
>I terminate with a 600 Ohm resistor (not critical, I've used 470 to 750
>Ohms) to an 8' ground rod.
When the distributed series inductance of a longwire is increased, the
impedance increases while the velocity of propagation decreases.
Slowing the velocity of propagation increases directvity of a longwire,
up to a limit of perhaps vp = .50 . When vp is slowed beyond the rate of
about .50 freespace pattern becomes a mess.
I have no idea of the distributed inductance of a slinky (it would
depend
on how far you stretched it out), but the surge impedance would be MUCH
higher than 600 ohms and would be critical. Since C remains the same,
the
more L per length, the higher the impedance.
If the antenna has F/B ratio without proper termination, it is only
because
the antenna has so much transmission loss termination is not critical.
I've done the same thing with ferrite coating, strings of beads on a
wire,
and lumped inductors. Four or more evenly spaced inductors will do the
same
thing as a slinky. In ALL cases, surge (and proper terminating)
impedance
went up into the thousands of ohms. If terminating (and feed[point)
impedance does NOT go up, you didn't change (electrically lengthen) the
antenna.
Tom
From: W8JITom@aol.com
Subject: Re: TopBand: Slinky availability
>A 9:1 balun xfmr kit using the larger FT114-61 toroid will sell for
>$3.50. You get the core, wire and instructions. The plastic case,
>connector, etc. can be purchased at Rat Shack. The case is optional
>anyway. I built one on some PC board scrap and it was in use for 7 years
>before the antenna took a lightning hit. I've built others inside
plastic
>plumbing caps.
>
>Add $5 to any of the above for S/H.
Why go through all that mess and expense when lumped inductors every 1/8
wl or so provide the same or better results?
Tom
=========================
From: W8JITom@aol.com
Subject: TopBand: Slow wave antennas
Let me describe quickly what the helical winding or lumped loading does
to the antenna, and what to watch out for.
All any method of loading does is slow the wave in the antenna antenna
down. It reduces the velocity of propagation. If the velocity of
propagation is slowed to 1/2 freespace, the antenna pattern looks more
like the pattern of an antenna twice as long. It creates nulls broadside
to the antenna.
There is a limit to how slow the wave can be made before the pattern no
longer improves, and it is generally at about 1/2 free-space speed.
Slower than that, or faster, and the pattern deteriorates. With too much
slowing, the pattern deteriorates AND sensitivity of the antenna
decreases. In either case the resulting pattern will not be optimized.
If
an error is made it is generally best to keep the antenna's current
propagation on the faster side of 1/2 freespace.
Like a regular Beverage, a slow wave structure wants to receive away
from
the feedpoint in the direction of lagging phase or termination.
The helical winding of the slinky mainly adds distributed inductance, we
all know series inductance retards current flow. The same slow wave
effect will occur with a thick dielectric surrounding the wire (it
increases shunt capacitance), a string of beads, or conventional
inductors in series with the antenna and spaced every 1/4 wl or less.
Any of these methods are just as effective, so the method used is a
mostly matter of personal choice. There is no "magic" caused by cramming
500 feet of wire into a 200 foot area, it's all current distribution and
phase. You will still have a 200 foot long antenna, just a bit better
one
if the phase and current is correct. If the phase and current is
distribution wrong, it will be a poorer antenna.
I used seven lumped inductances placed about every 1/16 wl on a 250 ft
wire. As I recall the best value was about 400-600 ohms XL, and
termination was about 1000 ohms with a number 12 or 14 wire eight feet
high.
I adjusted the inductances to the correct value for 160 meters. I did
this by exciting the antenna with RF and measuring phase shift from end
to end. Instead of terminating the antenna, I returned the far end
through a step down transformer via equal lengths of coax to a phase
meter.
Knowing that it is worse to slow the wave too much as not enough, it
seems unlikely a slinky stretched ransom amounts would provide optimum
performance. It would be pure blind luck if it was, and likely not
reproduced by the same luck in other installations unless the original
"inventor" made measurements of Vp and winding pitch and diameter, and
the installation was duplicated exactly.
I'm open to any technical correction on this. My experiments were done
in
the 70's, and my recollection is vague. But page 72 of Antennas and
Transmission Lines by Dr. John Kuecken seems to confirm what I recall.
Slow wave antennas will not work as well as a simple phased array
occupying the same physical area, but they are capable of being better
than a conventional terminated wire the same length.
Tom
===============================
From: "dhagert@mn.uswest.net" <mn.uswest.net@mpls1.mn.uswest.net>
To: <topband@contesting.com>
Date: Sat, 2 Aug 1997
I have been following the discussion on using the slinky for a beverage
antenna. I do not profess to being an antenna expert, but I always find
it easier to put the antenna up and do "on the air" testing before I
draw
any forgone conclusions from the "experts" that have never erected one.
Theory on paper is just that.
I went to the local Target store and found they have the 3" diameter
ones. After purchasing them, I found they are 90 turns @ 2.84" O.D. ,
which equates to 67 feet of wire per slinky.
I would like to find out where the orginal article was published so I
can
install them per the article for comparison. Any help that can be made
available will be appreciated.
Dale W0IR
Dale A. Hagert
3881 Serpentine Circle
Eagan, MN 55122 612-688-7155
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