In article , starman
wrote:
John Doty wrote:
In article ,
wrote:
So what would you think the relative 'resonant frequency' of the small
diameter and shorter Slinky Jr. be ? ? ?
One of the peculiar things about a small diameter helix is that over a
rather wide range of pitch angles and diameters it resonates at
approximately twice twice the frequency that it would if it were
stretched out straight.
Is there a formula that applies to a Slinky?
Not hard to calculate this with a helix of at least three turns will
result in an impedance of ~ 140 ohms:
Wavelength = WL
Diameter of a turn .35 WL
Circumference of a turn 1.1 WL
Pitch ~ 13.5 deg
Spacing between turns WL tan 13.5 deg (about 1.35 WL)
Seen from the side the helix should look like a sine wave proportional
to the size of an EM wave it is made for in air. From this you can
probably guess how it works.
A typical slinky would work in the microwave range.
I consider the helix to be a basic antenna in that it emulates the way a
wave travels in space. A reference dipole is like space terminated to a
passing wave.
--
Telamon
Ventura, California