It was the fall of 2003. I had just completed the 40 meter and 80 meter networks, and finally had time to turn to 160 meters. This band would be different.
Even though the elements were nearly 50 feet tall, there was very little mutual coupling between elements at 1.83 MHz. This meant that the feed point impedance value of each element would not change due to the presence of the others. That's good news, since several steps in the normal design process could be skipped. To the down side, the self-impedance of each vertical, before taking into account ground loss, is approximately 1 - j 350 Ohms. When directly connected to 45 feet of RG-213 transmission line, the loss across the line is around 12 dB. While that is a tremendous amount of loss, the result is a signal level which is still near the level of a long Beverage antenna. This is a fine receiving antenna, but way too much loss for transmitting. That's not a problem, however, since reception was all that I was after on 160 meters.
I built a network that included trimmer pots for setting the current magnitude ratios (more loss). All of the components were rated for low power use. Smaller toroids and silver mica capacitors were used. The whole network was built on a piece of perfboard, and placed within my standard enclosure. As the weather was becoming colder and wetter, I found a good day, and headed for the array with the long extension cord, signal generator, and oscilloscope. The network was adjusted until the desired 160 meter current ratios were achieved. I went back into the house, and looked forward to listening to the array on 160 meters.
Sadly, the performance was poor. This defied my experiences on 40 and 80 meters, where the same procedure resulted in symmetric performance between transmission and reception. What went wrong here? My initial guess was that although I measured the desired current ratios at the base of the six verticals, I was not measuring all of the radiating elements. Perhaps the transmission lines had become part of the antenna? Signal was leaking out of some unexpected and undesired point, degrading the pattern.
Here is a picture of the initial network. Please click on the picture for a larger view.
Winter has now descended, and outside work is on hold until the spring of 2004. I'm quite curious to pick up where I left off, and solve the mystery.
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