REQUIREMENTS ANALYSIS

The beginning

    The concept for my new tower system began in early 1991 when Frank, W3LPL, was at my house and commented: "Bill, your A4S at 55 feet on a crank-up tower doesn't even approximate an 'average' contest station, much less a competitive one."

    "Well", I said, "What do you suggest?" That started the ball rolling, and it hasn't stopped yet. Frank then used a small pad of paper and a pen and drew a plan of attack for me to pursue (the proverbial "Sketch").

The new antenna sytem had meet certain requirements

  • Incorporate stacked antennas where possible
  • Be able to handle a full size 3-ELE 40 meter beam, either initially or in the future, without modification of the structural design and/or implementation.
  • Incorporate PacketCluster(TM) node vertical antennas at 120 feet or higher.
  • Be as tall as possible, given the physical dimensions of the property and given a design goal of 90% guying with 6 foot elevated guy anchors. [90% guying means that the distance from the base of the tower to the guy cable (extended) entry point into the ground be no less than 90% of the distance from the base of the tower to the topmost guy point on the tower.]
  • Incorporate antennas for the following bands: 160M, 80M, 40M, 20M, 15M, 10M plus 144 MHz and 432 MHz bands for packet.

That led to the following specifications

  • From Frank, W3LPL, the initial antenna propagation specification was obtained: The 20M beam must be located at a height of 100 ft. This became the specification that drove the rest of the system design. This 100 ft 20M spec became the determining factor in ALL of the other antennas loactions on the tower, including the tower height itself.
  • The tower, because of the 90% guying requirements needed to be guyed no higher than approximately 140 feet. This was necessary due to the physical constraints in the property. With a gas pipline right-of-way and a septic building restriction line, the tower would need to be designed and implemented with precision.

The design proceeded

    With the 20M antenna at 100 ft and 90% guying limited by property restrictions to approximately 140 feet, the next specification that could be determined was the lower antenna in a 20M two-stack: 50 feet. This particular spacing was a solid performer at W3LPL's station, so it became the 2nd spec we "fixed". The models looked very good:
    Then, I decided to install CushCraft 40-2CDs initially, rather than design and build a 40M beam myself because I had never designed and/or built a beam antenna from scratch. The upper 40M antenna would be at one wavelength above ground (134 ft) and the lower 40M antenna at 67ft. The EZNEC model looked pretty good for the 2/2 stack:
    Now that 40 and 20 had been decided, that meant that the tower must be at least 134 feet high. Now what about 160, 80, 15, and 10? I still had plenty of real estate on the tower, so the decision on those locations would need to wait for the determination of the guy wire locations on the tower so as to not interfere with the beams. As far as rotating the beam antennas, I had a choice between side mounts or Ring Rotors - a decision that would be made later.

    Much of these remaining decisions about antenna placement on the tower will need to wait for other design decisions to be made. The Tower decision would be next.

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