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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Additional Batteries

Three deep cycle marine batteries were just not providing enough reserve capacity.  They charged quickly and on sunny days were fully charged by 9am even in the winter.  After dark, they drained quickly, too. Time to upgrade. Research showed a good battery for the money is a golf cart battery.  They are rated at 215 AH, 6 volts each, and sell for $89.99 at Batteries Plus.  We purchased two pairs and wired them in series/parallel to provide a rating of 430 AH capacity at 12 volts.  We didn’t run out of juice nearly as early at night but the first snow storm proved we needed still more.  Running without recharging for 3 days was impossible even with 430 AH.  Next purchase was a Morningstar Sunsaver Duo solar controller to replace the Sunsaver SS-20L.  The new controller allows two banks of batteries, meaning we can combine the golf cart batteries and the original deep cycle marine batteries.  We’re waiting for the next snow storm to see if this was the correct decision. Here’s a current peek inside the shed.  The batteries are on the floor on the right hand side.

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The Sunsaver Duo controller comes with a bonus.  It has a data port that provides information about the battery’s state of charge.  An adapter has been added that provides Web access and we can now see how much battery capacity remains any time.

After a few weeks of operation the new battery arrangement seems to be a success.  The radio bank and the peripheral bank both reach float before noon on a sunny day and neither bank has dropped below 12.0 volts during stormy spells.