First Measurements

Today we measured the actual height and the resonant frequency of the big vertical for the first time since it’s been installed. Amazingly the resonant frequency is exactly what it was designed to be, 2.9 MHz and the impedance is an ideal 35 ohms.   These measurements were taken with the tuner out of the circuit.

Height   56′ 3″

Resonant Frequency   2.9 MHz

Impedance         35 ohms

The top hat consists of the first 16 feet of the top guy wires.  We are assuming the effective area of a drooping top hat is a function of the sin of droop angle.  If so, a nominal droop of 45 degrees provides a factor of .707 effective area (.707 is the sin of 45 degrees).  A resonance of 2.9 MHz indicates the vertical is electrically 80.7 feet tall (468 div by 2 = 234.  Divide 234 by 2.9 = 80.7 feet.).  Subtract the actual height of 56.25 feet from the electrical height of 80.7 = 24.45 feet.  Compare this to the actual top hat diameter of 32 feet and multiply it by .707 which equals 22.6 feet.  Our assumption proves to be pretty close, off by only two feet which could be accounted for by the difference of the actual slope with the estimated slope. Or it could be just dumb luck, who knows.

The main purpose of today’s site visit was to restore the vertical to it’s original height.  Two sections had slipped down inside their adjacent sections by about 18 inches and the tuner could no longer find a match for 160 meters.  It’s hard to tell any difference with the naked eye but here is the restored appearance.  The tuner is able to once again resonant on 160 meters as well as all other bands.


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