Tom Sevart ...

^ "Frank" wrote in message
^ news:01c3fa02$2154f3c0$0125250a@rbhbhnosfpwihvvg.. .
^
^ 75/120 = 0.625 meters
^
^ Or, to put that in American, L in feet = 468/MHz.

I did use Amurican. Amurica is part of the international community and the
meter is the international standard measurement of length. Besides, it's much
easier to measure 0.625 meters on a bilingual yardstick, or meter stick, then
it is to measure 2.05 feet. It's also easier then doing the additional math
that you suggest.


^ 468/120 = 3.9 feet. This is, of course, the length of the entire dipole.
^ For each leg, you'd use 234/120 = 1.95 feet, or simply divide the 3.9 by 2.

Note that the formula I gave produces the length of each leg. The
relationship is that electromagnetic energy travels at three hundred million
meters per second (300,000,000 m/s) and a megahertz is one million cycles per
second (1,000,000 1/s). To find meters (the length of one cycle) divide
3,000,000 by the frequency in MHz:

300,000,000 m/s
-------------------
120,000,000 1/s

The seconds divide out and 'm/1' becomes just 'm', and the resulting value is
the length of one wave in meters. Note that the 000,000 also divides out so
the math can be abbreviated as 300/120. To find a half or quarter wavelength
it is generally easier to first divide the 300 by two (150) or four (75),
which are easily remembered, then it is to perform the second division on the
resulting value.

To be more precise the resulting value for a quarter wavelength would be
multiplied by the velocity factor of the wire being used, but since these
antennas are normally intended for receiving a wide frequency range such
precision is generally wasted effort.

Frank