Variables will mess up your test results. You can't begin to compare two antennas installed at different locations no matter how close. Even if both antennas are on the same lot, there are variables. One antenna must replace another in the exact same spot, power output, and even differences in time add variables. I disagree with the 5/8 wave having 2 Mhz bandwidth while the Sigma has 1 MHz. My tests on 11 meters shows the exact opposite when compared to a Maco V-58. I get 1 MHz on the Maco 5/8 and 2 MHz at 1.5:1 or less on the Sigma. This made a big difference in the ability to work both 10 and 11 meters off the same vertical.
The exception to the bandwidth rule is when you run these antennas far outside of the intended band. The gamma match on the Sigma with it's shunt feed will not resonate well outside of the bandwidth even with an antenna tuner. Then the 5/8 waves matching network works better with a tunner on other bands like 15 meters where the Sigma will not. The upside for the Sigma is it radiates less out of band harmonics then the 5/8 wave. That's just harmonics not RFI. The Sigma on HF can be worse then the 5/8 wave in terms of RFI without a balun.
Some of you know I rescaled the Sigma for FM broadcast use 15 years ago after testing many 5/8 waves for FM. Having great results with the Sigma on 11 meters I knew this antenna could do the same on FM. Working with it on FM gave me the ability to conduct many tests with calibrated field strength meters like the FIM-71. Accurate gain, ERP, and signal contours were extremely important to us since all my FM customers would be adjusting their transmitter power according to the antennas gain to meet their licensed ERP level.
Here are some basic facts. In order for an omni directional vertical antenna to have gain, it must lower the angle of radiation with respect to the antenna it is compared to. For one antenna to have a stronger signal then another means it's radiation angle is lower. The lower the angle of radiation, the stronger the signal will be on the horizon. This is the case at 10 miles, or 50 miles. It just becomes more evident as distance increases. The only exception to the rule of lower angle radiation equaling more signal close in would be when the two stations are at extremely different heights.
For example if the transmitter antenna is located on a 6000 foot mountain and part of the desired coverage area is almost directly underneath the antenna. In this case most of the signal will pass way overhead. In the FM broadcast market we use beam tilt to refocus some energy downwards. This doesn't present a problem with the average 11 meter installation. Even if it did, as soon as you get out several miles the effect tends to diminish.
We had an engineer at two of our first LPFM installations that was kind enough to perform some tests for us. The stations were told by Ramsey that the Comet 5/8 wave would double their ERP. Sounds like a real 3 db increase, except they overlooked the 5/8 wave wasn't compared to the standard 1/2 dipole. They bought the FCC certified 50 watt transmitter and the Comet 5/8 wave thinking they were going to get 100 watts ERP. The Comet is a real 5/8 wave with full 1/4 wave ground radials.
We came up with about 1.8 db5/8. That's a new term. it means 1.8 db over a 5/8 wave. Below are the real world results of what happens when the ONLY VARIABLE is going from a 5/8 wave to a Sigma design from the company that installed the antenna on the towers for the clients. Keep in mind these were early tests designed to confirm the claimed 3 dbd in order to determine the appropriate TPO to reach 100 watts ERP after coax loss. The engineer reduced the transmitter to 20 watts at 35 feet. Later the stations increased to around 50 watts TPO at 100 feet with significant range increase. I removed the name of my product because I'm not advertising, I'm educating.
Donald,
Antenna received, tested and shipped to our client, they are going to be delighted with this system:
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Lightly populated urban area flat horizon most rooftops below 30 feet:
Comet 5/8 wave @ 35 feet AGL and 20 watts TPO: Signal verge 4 miles best - 3 miles radius - 4 - 5 miles poor reception then fade out.
--------- .82 wave @ 35 feet AGL and 20 watts TPO: Signal verge 6 miles best - 5 miles radius - 6 - 7 miles acceptable reception then fade out.
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Rural area mostly farm land without obstruction flat horizon:
Comet 5/8 wave @ 35 feet AGL and 20 watts TPO: Signal verge 6 miles best - 4 miles radius, 6 - 7 miles poor reception then fade out.
--------- .82 wave @ 35 feet AGL and 20 watts TPO: Signal verge 11 best miles - 9 miles radius, 11 - 12 miles acceptable reception then fade out.
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I used the Comet 5/8 wave as a comparison because both antennas offer similar vertical radiation properties. The efficiency of the --------- .82 wave speaks for itself, it delivers almost double the performance of the 5/8 wave, there are no questions left to answer except "where is your --------- .82 wave"?
