For what it is worth, I pulled up the spreadsheet again and identified some
"optimums"
However, it is important to note that the optimums located are for 160 only.
I have not tried to integrate use on 80 as well. There are compromises with
any antenna, the beverage is no exception. Most guys want it to work on
both bands and will sacrifice performance one way or another to get it.
If you want the spreadsheet, I'll be glad to share it. However, it is over
426K in zip format and over a megabyte unzipped. Let me know what version
of Excel you have. I use Excel 97 as part of the office suite. If you have
a newer version, you should be OK. An older one and I'll have to save it to
an older format.
I must caution that none of these antennas have been built side-by-side for
comparison tests. I have only one 5 acre farm in central Minnesota and
would need 10 more twice as big and at various locations to test over
different soils.
There should be about 50 pages of fine print here but what the heck...
Frequency 1.832 mHz
Vp .98 .95 .90 .85 .80
1st 135 137 141 145 149
2nd 406 413 424 435 447
3rd 678 688 706 725 745
4th 949 964 989 1016 1044
5th 1220 1239 1272 1306 xxxxx
These are in feet and are based on velocity of propagation in the line.
I received several good comments about the distortion of the wavefront
itself right at the surface of the earth due to Vp alone. I have not
attempted to compensate--only to assume that the beverage would be low
enough to make the differential between the "air" and "wire" wavefronts
identical.
Tom Rauch questioned the formula for incorporating "tilt" into the equation.
No attempt was made to measure or compensate in any way for tilt.
With that being said, let me suffice it to say this: The so-called
"optimums" are mathematical optimums. In practice, the model indicates that
you don't need a micrometer to find a good beverage. Plus or minus 20 feet
doesn't seem to matter much. Second, the Vp of your line is damn near
impossible to measure in nature--how to you get channel A and channel B of a
scope at both ends of the beverage at the same time! Third, it is difficult
to model the effective charge contribution per unit length the wavefront in
air contributes to the wavefront in the wire. The spreadsheet looks only at
phase relationships along the length of line for signals arriving in line
with the antenna.
The bottom line is this... if I were to put up a beverage, I would start
with lengths reported in the ON4UN book--particularily the compromises
between 160 and 80 lengths.
Let me know what version of excel you have if you are requesting a copy.
Ford-N0OQW
ford@cmgate.com
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