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Author Topic: Slinky for 10 Meters and other bands when...  (Read 1308 times)

Posts: 76

« on: March 23, 2007, 04:41:33 PM »

I get my general in a few months.

I'm thinking of this guy:

On two 20-30ft masts on the roof.  1. To pickup sporadic E on 10 meters and for when I pick up my general ticket in a few months and grab an IC-718.

I couldn't find alot out about this dipole on the web other then it's a good idea to run a rope through it to support it mechanically.

What I'm curious about is how does one set the band for this guy? (Not trusting the manufacturer for a minute that it's "magic") Is it all done in the tuner or is it the actuall length that you stretch the slinky out? If you think about it a slinky is the same length of wire regardless of how far you strecth it.

As always your views are appreciated.

Posts: 17482

« Reply #1 on: March 23, 2007, 05:50:00 PM »

If you can put that up between two masts on the roof, you have room
for a real wire dipole for each band you want to operate.  I think you'll
be happier with that.  If they don't fit between the masts (or hanging
from one mast as an inverted vee) then run the center of the antenna
as far and as straight as possible, then bend the ends to run out to
corners of the yard or whatever you have to do to make them fit.

It is true, folks HAVE used slinky dipoles before.  And with a tuner and
balanced line, I'm sure it radiates.  The resonant frequency will depend
on how far out you stretch it and how the coils are arranged.   Here
is an example:  say that you tie the end off to a particular length and
bunch all of the coils by the feedpoint - this will make a center-loaded
antenna and you can get a good idea of the resonant frequency by
calculating the coil inductance (from the number of turns, diameter and
length of the coil) and the total length of the antenna, since the few
turns in the rest of the antenna won't have much effect.  Now if you
move all of the turns to the middle of each side of the dipole you have
the same inductance, but the antenna will resonate at a higher frequency.
If you move the turns to the end is will resonate even higher.  So by
moving the turns around on the wire you can vary the resonant frequency
by some amount - perhaps as much as 2 : 1.  But you may find that,
unless the Slinky is made from bare metal so you can short turns together
to remove them from the circuit, it is difficult to get it to resonate as
high as 10m.  And moving the coils around isn't a convenient thing to
do whenever you want to change bands, especially if it involves
climbing up onto the roof and lowering one or both masts.

I think you'll be a lot happier with wire dipoles.

Posts: 4283


« Reply #2 on: March 23, 2007, 06:13:14 PM »

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