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Author Topic: Slinky Antenna Ideas Offered and Wanted!  (Read 2173 times)
XE1UFO
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« on: March 09, 2004, 03:16:16 PM »

I just finnished building a couple of portable Slinky doubletts for some friends and one for me. All have 30-50 feet of 300-ohm television twinleed for feedline. My last one has two Slinkys on each side, because I want to try 80-10 meters.

Here are a few things I have learned about Slinky antennas.

1. Slinkys will rust if not protected. What you need to do, as with most metals (other than stainless steel, brass, copper or aluminum) is give your Slinkys a couple of coats of automotive-type spray paint. Then they will last a long time out of doors.

2. To join two Slinkys end to end, take your thumb nail and push the crimps around until they slide off. (They are not as tight as they at firts appear.) Once you get the crimps off, force a small screw driver or other objct into each crimp to open them up a bit. Then slide the TWO crimps onto ONE Slinky, and then feed the SECOND Slinky into the two crimps. I like to have at least one half turn overlap between the two Slinkys. Then I use an electrician’s crimping tool or a pliers to re-crimp the two together, and then solder them together.

3. You can get the Slinky to take solder if you do a light sanding of the metal first.

4. 4 Slinkys end-to-end are used as a long-wire by Dave, N9ZRT, with success.

5. Also, don’t just think horizontally. Slinkys can be used as shortened helical-mode verticals. Think: a 40-meter vertical 15 feet long.

6. Though technically a Slinky has about 63 feet of wire, a quarter wave on 80 meters, if you stretch it that long, it is no longer posssible to return it to its condensed form. In other words, you would destroy the Slinky. In that case, just use regular wire.

7. Rule of thumb is:
a. 1 Slinky: 40-meters and higher, at 15 foot stretch.
b. 2 Slinkys: 80-meters and higher, at 30 foot stretch
c. 4 Slinkys: 160-meters and higher, at 60 foot stretch
* These dimensions are for quarter-wave vertical, or PER SIDE on a dipole or doublett.

8. Backpack portability protection: Find two plastic jars, at least 3 inches-wide mouth, and at least 5 inches deep. (peanut butter, etc. Hint: Remove peanut butter first!) Glue the LIDS back to back screwthreads away from each other) Use this as a center for your portable Slinky dipole. Fasten the Slinkys with tie-wraps through both lids. When not in use, compress
the Slinkys and the internal support line that runs through them and the lids (20# fishing line or other) screw on the plastic jars for in-transit protection. Now you have a nice 11-inch tube in your backpack or car trunk. Or try something with PVC end caps? Attatch the feedline with aligator clips or use your imagination.

9. Slinkys have also been used as loading coils for portable hotel-room verticals. Stretch the Sinky 4 to 5 feet up a PVC or wood dowel support and connect the top to a 5-foot telescoping whip from Radio Shack. Use at least one 16-foot counter poise. Use aligator clip to select number of turns needed.

10. Inside the XE1RCQ Radio Club building, we have
some very noisy flourescent lights. Any inside antenna picks up lots of noise -- EXCEPT the Slinky dipole hung directly under the lights!! Amazing!!

Hope this wakes up some ideas out there!! Any more
Slinky ideas?

Steve, XE1UFO
xe1ufo@hotmail.com
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WS8E
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« Reply #1 on: March 21, 2004, 10:20:15 AM »

   I was in a discount store yesterday afternoon and bumped into a display of Original Slinkys....a little voice inside my head said ....loooowwww baaaaannndss  ..... so I picked up a couple thinking I might figure out a way to string them up in my attic and load them up on 80 mtrs or at least 40....
    When I got home I started counting coil turns (86).  I wanted to calculate the overall length of the conductor.  I got stymied when I realized I'd have to hunt up a ruler or something to measure the diameter of the spring.....Then it hit me!  I am probably not the first one to think of this....a few key clicks later one the ARRL web page and I was  reading a copy of an October '74 QST Article by W7CZB.  The article is based on a Slinky Junior.

I also found this short paper:

http://www.njqrp.org/meetings/09-28-01/slinkette.pdf

Neither paper is very technical and I'm wondering:
 
1. Why did W7CZB choose Slinky Junior instead of the Original?
 
2.  How important was/is the amount of stretch?  How did W7CZB arrive at 3 slinky Jrs per leg?  Trial and error?  

3. Your post suggests 1 slinky is 1/4 wave at 40 mtrs or 10 mtrs.  However, my measurements and calculations (diameter = 6.8 cm * Pi x 86 turns) indicate that a standard slinky is about 18.372 meters of wire.

4. Has anyone developed any design equations?

5. Is the inductance of a streatched slinky low enough that it can be thought of as essentially a wire?

6. What is the speed factor of slinky steel ?

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AF6WI
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« Reply #2 on: December 01, 2004, 01:47:32 PM »

See also
http://www.nonstopsystems.com/frank_radio_antenna.htm
for a 2-slinky dipole. I've just finished it, but I haven't yet had the opportunity to string it up.

Phil
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XE1UFO
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« Reply #3 on: December 30, 2004, 09:57:28 AM »

Right now I am working on a 4-Slinky per side doublett for 10-160 meters.  Let's see: this would be 60 feet total length, and fed by 300-ohm twinleed.

For hotel balcony work, I have two Slinkies in series, which I stretch up a 12-foot telescoping fishing rod ($9.99 from Wally World). The pole is usually at a 45-degree angle. I connect to the middle (just one Slinky) for 40-10 and the bottom for 80.  Have a 20-foot #18 cable for the ground side, with a large clip to connect to the  copper plumbing system of the room. (Most older hotels here use copper).  These clips are sold also at Wally World (99 cents for two).  The blister pack says "Replacement battery charger clips".  These are just the right diameter for copper pipe.

Blessings for 2005!

Steve, XE1UFO a.k.a. KA5SUT
Santiago de Queretaro, Mexico
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WA8MEA
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« Reply #4 on: March 15, 2005, 08:11:05 AM »

If portable operation is the goal, there are these gadgets, too:

http://www.eham.net/reviews/detail/2363

73, Bill
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XE1UFO
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« Reply #5 on: May 13, 2005, 11:04:05 PM »

To Tom WS8E:

Yes, Tom, you are absolutly right: An original toy metal Slinky contains the equivalent of APROXIMATELY 1/4 wavelength of wire at 80 meters (You will notice that Slinkys have plus or minus a few turns.)  But if you check out any good antenna book or the ARRL handbooks, you will see that for any helically-loaded antenna (such as the Slinky) the rule of thumb is you start with TWICE the necessary quarter wave of wire for a quarter wave antenna.  The capacitive coupling between turn has the effect of shortenning the antenna electrically.  Hope this helps!

Steve, XE1UFO    
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DD3LY
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« Reply #6 on: February 18, 2006, 12:01:56 AM »

Slinkies are by far NOT resonant where we would like them to be! The stray capacity between the edgewound metal strip prevents this. Therefore I recommend another way: You may use a spiral spring door which normally used for electric fences. This is a zinc plated steel spring which is self supporting /hence does NOT need a rope for supporting like the Slinky does), does not rust and is really CHEAP: Here in DL I bought a couple for 14.ooEuro including shipping.
These springs do the same job as good as the Slinkies do with less effort (mechanical and financial).
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DD3LY
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« Reply #7 on: February 18, 2006, 10:24:59 PM »

Searching the web I found such door springs for electric fences in the US too. Some offered were even longer (each up to 7m) and there was one offered which was made from stainless steel! The Slinkies I have seen were made from simple carbon steel which rusts within ONE rain if they were not protected by a varnish. But I have found a gold plated Slinky too in the US for some 90 bucks, hi ;-))
Anyway, a Slinky has not enough mechanical tension to stay straight by itself. It needs a rope for support. A door spring for an electric fence IS self supporting, it has a higher mechanical tension. With three insulators made from epoxy circuit board or even from short pieces of monofilament fishing line and some meters of ladder line you have an antenna which is strung up within seconds. Use your balanced Z-match or maybe your SGC-autotuner and start working. It's a real emergency antenna too...
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XE1UFO
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« Reply #8 on: September 08, 2006, 11:06:16 AM »

Dear Friends,

We just moved.  At the moment, my only up-and-working antenna at home is:
--a 40-meter dipole in inverted V fashion, about 20 feet at the vertex on top of a one-story house, using a crappie pole as a support.  The ends are only about a foot off the cement roof, which has lots of rebar in it.  The lot here is too short for a horizontal dipole for 80.

Well, Wednesday night I needed to check into our Mexican 80-meter SSB national emergency net (Red Nacional de Emergencia) on 3.690.  While my antenna matcher would tune out the SWR, nobody could hear me.
 
So in utter frustration, I opened my junk box and I found ... a bunch of Slinkies!!   So I grabbed a couple, and soldered an alligator clip on one end of each of the Slinkies, twisted the opposite end into a loop to tie a rope to.  Then I clipped them onto the ends of my 40-meter dipole and stretched them out about 8 feet.

My MFJ-269 Antenna Analyzer tells me that the dipole alone is centered at 6.873, with another pronounced dip on 21.448 Mhz.  I am sure all the rebar in the roof is detuning it considerably from the center of 40 meters.  
 
But with the Slinkies, I have now good dips at: 2.999, 4.200, 9.800 and 18.060.  I am getting very good signal reports from around Mexico tonight. (I am using my Dentron Jr. Monitor antenna matcher.)

So now I am dreaming.  I am almost finished rebuilding my 40-foot mast.  Then change out the 40-meter dipole for an 80-meter version.  Change out the coax for a length of 450-ohm ladder line which I found in my storage.  Then add TWO Slinkies at each end and ... 160-10 meters?

If you think I am half-crazy, that is because you only half know me!

73's.

Steve, XE1UFO KA5SUT
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XE1UFO
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« Reply #9 on: September 08, 2006, 11:23:34 AM »

In my original post, I wrote:
===============================
7. Rule of thumb is:
a. 1 Slinky: 40-meters and higher, at 15 foot stretch.
b. 2 Slinkys: 80-meters and higher, at 30 foot stretch
c. 4 Slinkys: 160-meters and higher, at 60 foot stretch
* These dimensions are for quarter-wave vertical, or PER SIDE on a dipole or doublett.
==============================

For the very first time in my life in the last three minutes, I made a mistake.  The measurements are for the TOTAL length of your doublet.  The rule of thumb should be approximately 7-8 feet PER SLINKY in you antenna design.  

Hope some more people will post some Slinky antenna ideas!
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DD3LY
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« Reply #10 on: May 25, 2007, 01:21:04 PM »

Let's think about the Slinky as a type of an emergency antenna:

- Any SHORT antenna has a low efficiency and LONG (halfwave) antennas have a sufficient efficiency.

- Short (or small) antennas HAVE a small usable bandwidth and their resonant frequency is NOT calculatable in most cases.

Concerning a spring loaded antenna (the spring to load it mechanical and electrical) I recommend to use NO slinkies, as their pull force is much too low for unsupported application. So called "door springs" for electric fences are about as cheap and self supporting.  You can find them in the US in farmers shops or you ask a farmer where to buy them. Two pieces of  bungee rope from your DIY shop will do the rest to the next tree, house or mast, even in a storm.

What you really NEED if you feed a slinky or ANY other short antenna (dipole or monopole), which ARE a short compromise antennas, is an antenna tuner with a high efficiency. A US ham (AG6K) wrote an article in the QST named "A balanced balanced antenna tuner" ( you can find it in the web: http://www.somis.org/bbat.html), which shows how to build such a high efficient antenna tuner for the high bands. Surely you will be able to build it for the lower bands too, with different parts. The famous Z-match with its "desperate" multiband circuit makes many compromises. All these compromises are added and sudenly you lose most of you power and make QRPP. Anyway, I recommend VERY much to feed such a short loaded dipole by using ladder line, NOT via coaxial cable.

For a really good emergency antenna for professional services I see a magnetic loop which is really small, has NO dead zone, is NVIS capable and needs absolutely NO supporting points (maybe it needs a rotor, hi).

The slinky IS a just something to PLAY with, in my eyes, if you have free space under your roof and an SGC antenna tuner and you local authoroties forbid outside antennas. But there are several other good ideas for such a case, just search the web for "stealth antennas. There is even a mailing list for this topic in YAHOO.

I always wonder how MANY fantastic results and astonishing reports are given for "miracle antennas" and if you take a closer look you can see that the inventors have made theirs contacts with modes which you can't compare (e.g. voice/SSB versus PSK31) as these modulation types have VERY much different requirements for signal/noise ratio. That's NOT honest! Such manufacturers simply wnat your best: YOUR MONEY!

So you need to THINK!
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WA4LDA
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« Reply #11 on: August 03, 2008, 10:45:33 AM »

Well, for what it's worth, I have a four-slinky doublet stretched about 33 feet, end-to-end, in my attic, and have had good results with it on 80, 40, 30, and 20 meters.  I feed it with 300-ohm open twin-lead (insulated, but with openings, so it is kind of like a cross between ordinary flat wire, and ladder-line), coming out of an MFC VersaTuner II.  No idea what the mismatch between the feedline and the antenna is; I assume it's probably horrible.  Regardless, I've worked SSB from here in Virginia to Italy (the other guy had a world-class antenna array, however), and both CW and SSB all over the continental US.  Judging from my contacts, it would appear to radiate off the sides on 20, off the ends on 40, and every which way on 80.  But that's just a guess and might reflect more about when I operate those bands than anything else.

With 100 watts from my Yaesu FT-897 (and from a Kenwood TS-430 before that), I tend to get a lot of S6-S7 reports on both modes within 1000 miles, when conditions are good.  Out towards the west coast, about 2000 miles, I hear more S5-S6.  Not going to win any contests with this thing, but it was cheap, easy to construct, covers several bands, and actually works.
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M3WIU
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« Reply #12 on: March 03, 2009, 02:35:32 PM »

Sir
Can u help, i have mounted a slinky in a room, wich i got from u. But when i use a z11 pro ATU on 20 meters i get a high swr over 3.0 and when i work 15 meter on the slinky i get a swr of 1.5 buy i can not be heard and i can not hear a guy from just over the town.....?
Do u know what i can be doinhg wrong? Any help .
Thank you


Any help any one please.

robertlewis2000@hotmail.com
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M3WIU
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« Reply #13 on: March 03, 2009, 02:38:58 PM »

Sir
Can u help, i have mounted a slinky in a room, But when i use a z11 pro ATU on 20 meters i get a high swr over 3.0 and when i work 15 meter on the slinky i get a swr of 1.5 buy i can not be heard and i can not hear a guy from just over the town.....?
Do u know what i can be doinhg wrong? Any help .
Thank you
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G8JNJ
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« Reply #14 on: March 04, 2009, 03:23:51 AM »

Hi All,

Slinkies are a bad idea for several reasons.

They have a high resistive loss, the capacitance between turns can result in unfavourable self resonances and the feed impdance varies with movement.

When fed with a tuner, a simple length of wire is usually 2dB more efficient.

Take a look at the bottom of this web page.

http://g8jnj.webs.com/compacthfantennas.htm

Martin - G8JNJ

www.g8jnj.webs.com

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