[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Longitudinal Wave Experiment
Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>
> >> I would venture further and say that radio waves cannot be detected along
> >> the ground (or at least they will be severely diminished.)
> > Not sure what you mean by that, but ground wave transmission is the
> normal mode for ALL commercial BC stations.
> I'm talking about the ground plane, not the ground. The ground plane for a
> quarter wave antenna is the surface between the earth and the atmosphere,
> not the earth below the surface. By definition, the ground plane is zero
> volts wrt a resonant quarter wave antenna.
I am talking about the same ground plane. Not quite sure what you mean
by your definition, or that last sentenc, .but a grounded vertical
antenna (or one fed between the base and the ground) has an equivalent
image in the earth, fed with the opposite current polarity. Input
impedance and reactance are exactly half those of an isolated half-wave
dipole. The radiation from the vertical antenna is vertically
polarized, and the maximum field strength is at the ground level (or
angle, if you prefer). Along the same lines, a TC is equivalent to a
very short vertical helical radiator with capacitive top loading, and
will excite the same currents in the ground.
> >> How many HAM operators do you see trying to receive HF with antennas
> lying on the ground?
> > A number of people have used them quite successfully. It's easy,
> particularly where the soil conductivity is as low as it is in most places
> on land.
> This isn't the same thing. Lying an antenna on the ground is different from
> burying an antenna or sinking a ground rod. When I say "lying an antenna on
> the ground," I mean literally lying the wire right on the surface of the
So do I. Right on top of the ground, weighted down with bricks or
No ground rods, no aerials, nothing is buried. The wire is flat on
> the ground.
The reason this sort of scheme can work is that since the "ground" is
by no means a perfect conductor, the equivalent ground plane is below
the surface of the ground and is not a perfect "short"; there can be a
voltage drop along the surface which permits reception of
horizontally-polarized signals. If you lay an antenna on top of a
perfectly conducting surface there can be no horizontally-polarized
signal present. As is the case of the vertical antenna, there is an
image antenna just below the surface and its field will exactly cancel
that of the one just above the surface.
> I've put this experiment to a friend of mine. We're going to get two 20
> foot lengths of 4.5" OD plastic pipe and tape two 40 foot long wires to the
> pipe 4.25" apart. In the middle of these wires we will use the half wave of
> a nearby 1390KHz radio transmitter that happens to be in the line of site
> from my yard. The long pipes will lie directly on the ground and we will be
> able to turn them to test for angular alignment with the radio station.
> A crystal radio will be placed across the two wires in one test to see if
> there is demodulation. Then the pipes will be lifted as high as possible to
> see if there is a change in performance. I'll also measure voltage at the
> ground level and at a higher level. We will also conduct these measurements
> with the pipes rotated in different angles wrt to the transmitter.
You are making a horizontally-polarized antenna and, in principle, is
should have zero output when it is oriented perpendicular to a line to
the transmitter, whether or not there is a ground present. When you
rotate it to be parallel to that same line there will be some signal,
because there will be some voltage gradient present in that direction
due to the relatively low conductivity of the soil. Single-wire
antennas of this sort were designed and build by Harold Beverage around
the end of WW1, and used for directive reception (maximum output for a
VERTICALLY polarized signal was along the length of the wire). This is
the well-known "Beverage Antenna" and principles of its operation are
given in any good antenna handbook such as that by Henry Jasik. Take a
look at one you'll get a better idea of what is going to happen in your
experiments if you conduct them very carefully to avoid spurious results
due to unbalanced connections, etc.
> I will also cut three metal pipes. One will be 3 times the wavelength of
> the half wave, one will be three times the length of the full wave, and one
> three times the length of pipe where the nodes are spaced equal to the half
> wave of 1390KHz. If there is a longitudinal component to this wire
> arrangement, it will cause these pipes to mechanically resonate.
You're talking about over 1000 feet of pipe. Good luck and high
ambition! By the way, why will the longitudinal wave excite the pipes
to vibrate and how are you going to observe any mechanical resonance of
those long and mechanically lossy (friction with the earth and the wire
> The purpose of this experiment will be to see if there are any clear
> indications that longitudinal waves are present.
What will be the manifestation of the longitudinal waves that you are
looking for, and how will you tell if you've observed it? Waiting for