Topband: Beverage Length

[Ford Peterson]

Late last winter, I was curious about the optimum length of a beverage.  I
set out to decipher why the length was so important.

Schroedinger (the physicist) discusses the traveling wave phenomena.  While
reading Schroedinger's Kittens and QED, I theorized that the optimum length
of the beverage had to do with the way the traveling wave in air added (or
subtracted) from the traveling wave in wire.  I prepared an Excel
spreadsheet to investigate.

The spreadsheet places a 1.830 (or whatever freq is being investigated)
waveform in cells of the spreadsheet--one cell per foot.  Likewise, on the
spreadsheet, the same wave in wire is delayed by the vf of the lineand
again, one cell per foot.  The only place the two signals are in perfect
phase is the starting point--the termination.

I theorized that the electrical charge along the wire was being added to by
the traveling wave in air as it passes.  If the wave is advanced, it added.
If retarded, it subtracted.  If not in alignment with the axis of the
beverage, the phases became so confused as to be insignificant.  The bottom
line is that there are optimum points where the electical charge at the
feedpoint is at a maximum.  Coincidentally, these "optimum" lengths
confirmed within feet of other experimenter's empirical evidence when using
"apparent" ground depths that were very believable.

Clearly, knowing the vf of the line is very important to this type of
analysis.  The velocity of propagation is difficult to estimate because the
apparent ground return path of the antenna has nothing to do with the
physical height above the earth.  Real ground may be 3 feet beneath the
surface and it may be 30 feet beneath the surface.  The notion of placing
the beverage at 10' is optimum is only a guess at local ground conditions
compared to those conditions at test sites that determined 10' to be best.
Many variables at play.
To estimate my ground conditions (loamy black soil, miles of open corn
fields, etc.) I laid a 500' piece of #12 insulated wire on the ground in a
large loop.  Both ends terminated near a 10' ground rod outside the shack.
I used an HP606 signal generator to feed signal into one end and measured
the time delay to reach the other end (using a 250 mhz scope).  Given the
known length, I had my vf when laying on the ground.

I further figured that the beverage is just a transmission line with the
apparent ground being the return path.  Using transmission line formulas, I
attempted to determine my ground depth.  After much screwing around, I now
believe my apparent ground at 1.8mHz to be about 3.5' in the area of the
beverage.

There were many interesting observations from my experiments.

First, the apparent ground was not the same over frequency.  The vf of the
loop went from 50% at 500kHz to about 80% at 40 meters.  160 was about 60%.
(remember, this is with the wire laying on the loamy ground).

Second, the length of the beverage can be cut at a point where the desired
signal is many db down from what is possible under "optimum length"
conditions.

Third, the termination impedance should be predictable once the apparent
ground depth is known.

Fourth, controlling the depth of ground by laying down a pair of wires (like
a transmission line) should allow one to control the vf along the length.

And finally, by placing 349 degrees of phase shift into the line every 1/4
wavelength (in air), the traveling wave in wire can be shifted into optimum
(advanced) condition, thereby alowing an unlimited length of beverage to be
used.  Normally, the absolute maximum length of a beverage is somewhere
around 1200 feet as I recall--depending on height, ground conditions, etc.
In my model, after about 2 wavelengths the "optimum" signal level never
repeated and in fact went down--this has been confirmed by many published
experimenters.

I hope this isn't too long and confusing.  If you are interested in my tests
or the spreadsheet, email me direct.

Ford-N0OQW
ford@cmgate.com


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