Re: My Thoughts on a Slinky Stretched-Out on an Eight Foot Long PVC Pipe
- From: nm5k@xxxxxx
- Date: 30 Oct 2005 16:57:28 -0800
>MK - I like this phase " dummy load on a stick. " :o)
It's no joke though. The "super resonator" hustler coils are
the worst. The 80m version is an exhibition in excess coil
loss. They did this on purpose. To make it easier to "match".
Add enough loss, and anything will look good as far as a
match. Same principal used as the B&W antennas that
use resistance to acheive wide bandwidth. In "small"
antennas, wide bandwidth is actually undesirable as far
as efficiency. The best mobile whips will use very high Q
loading coils.
The silly part is it's very simple to match any short mobile whip.
A single small coil at the base will do the job just fine.
With helical, or even lumped coils, the "matching" coil can
actually be wound into the base of the helical whip, or, can be
a portion of the lumped coil used. The best helical whips will
use a "lumped coil" winding scheme. *Not* a constant wind.
Winding the bulk of the loading coil into the upper section of
the whip improves the current distribution, which in turn directly
effects the efficiency also. Also, take a look at most "hamsticks"
, CB firesticks, etc, etc... Most will wind the matching coil into the
base of the fiberglass stick. Thats what those few turns at the base
are for. You don't need the external matching coil in that case.
Also note that the better sticks wind the bulk of the loading coil
towards the top, and then add a stinger as the needed capacitance.
>OBTW - Slinky Antennas are the most popular
>Antenna 'type' that is sold on eBay.
I imagine cheap "fake" strats and telecasters also outsell
the real deal fenders. That doesn't automatically mean I need one.
BTW, here is another pix of the beam on ground, but assembled.
http://web.wt.net/~nm5k/fd01b028.jpg
It's a full size yagi. Those are traps only, not loading coils.
The reflector is a full 32 ft span. It's a cushcraft A4S that I got
free for yanking a tower down one time. It's a pretty good design.
You see 4 elements, but it's actually a 3 element yagi. The element
spacing is more optimum vs a smaller beam using the same
reflector. The "short" 2nd element is actually the 10m reflector, and
that is the "back" reflector side of the beam. It gives "near" full
size performance on the three bands. "20,15,10". You think that
thing won't hear a knat fart in Africa on 19m? Hummmmm...:)
You'd never wanna use a slinky again...:(
The erection process...
http://web.wt.net/~nm5k/fd01b032.jpg
The tower is tilt/crank, and we just uprighted it in that pix.
It is then cranked up. It's 31 ft at the top. Not real high, but not
bad for a tower that collapses to only 7 ft.
That base is *very* heavy ship steel cut at a shipyard with a
CRC plasma cutter bed. That tower *and* beam stands up by itself,
even cranked up. Out in a field. No slab! It's a stout boy...
The guys are only backup protection. I'm crazy, but I ain't no fool.
BTW...No grounds were used in this apparatus. At all.
It's a complete antenna. The feedline is decoupled
using a coiled coax choke at the feedpoint.
MK
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