Jeff wrote:
"m II" wrote in message news:_0Rqd.20232$VL6.6397@clgrps13...

Rob Mills wrote:

I've always had good luck with the Slinky. I've used them indoors in both
vertical and horizontal configurations. Looks to me as a helical wire
(slinky) stretched over, lets say 20 ft would have a whole lot more capture
area than a 20 ft wire.

Ok, it could be the equivalent of a longer wire, but I doubt it. The
induced forces in the slinky would tend to cancel each other out when
the coil is going in opposite direction.

Say the signal is coming in from the side. It will induce a current in
the first half face of the slinky. When the signal hits the far side
face of the slinky, about three inches away, the wire is basically
going in the direction opposite to the first side. This would tend to
cancel out the current in the first half.

I'm just guessing here, but I would think only the (in this case)
horizontal component, not the vertical, of the slinky would add
anything significant to the usable radio signal.


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Wrong on both accounts. Go back to basic electromagnetism
and study its effects on a coil of wire. This basic a.c. generating principal.
i.e. a revolving coil in a magnetic field. The reason why in ac the current
is alternating between + and - is the reversal of magnetic poles. RF by
its very nature is somewhat of a very high speed a.c. RF is actually
electrostatic rather than electromagnetic. There is no way an electrostatic
signal is going to cancel itself in a helical antenna. Helical antennas have
been used by NASA and other Govt agencies for years. They are a very
good antenna for signals that come down from the ionosphere at virtually
any angle in relation to the horizon. There is a company called RF Systems
that make fairly decent vertical antennas using this principal. The inside
of the pvc tube is a helically wound antenna terminated with a MLB.
I have one and it works very well,,, one of the most quiet antennas Ive
ever used. The instructions that come with it list the ratio of horizontal
to vertical surface,, I just dont remember what the numbers are. A
slinky with a MLB on one end should make a very decent antenna as
long as its stretched out and not all bunched together.


I'm tempted to think the helical wind may contribute more to the
actual tuning than the capture area. I've always understood 'quieter'
to mean an overall reduction in signal level. In my opinion, it's the
radio's job to cut out the noise, not the antenna's. Directional gain
notwithstanding, of course.

We have to be careful not to inject the signal in the same direction
as the end of the winding. It may start resembling a coil in a
generator, with the wire crossing the lines of flux at roughly ninety
degrees. I can't see why a coiled antenna should act any differently.


The stretched out slinky would tend to validate my position. As you
make it longer horizontally, the more signal it can pick up. The
slinky is the same length of metal whether it's pulled out two feet or
ten feet. if your statement were correct, it should work as well at
EITHER length. It doesn't, so I remain unconvinced.

I did say proper measurements would be in order to get a real
evaluation. Does someone have access to an RF signal generator and a
radio with a real, working S meter? We could find out in no time.

Broadcast a signal at 5 MHz and measure signal at, say, four lengths.

Repeat, going up the frequency scale in even increments.

The proximity of the rf generator may well mess this up, though.

Graph radio response.



mike