I was off this reflector for the two weeks after Dayton. Someone may
have mentioned some of what follows. Cushcraft showed up with two new
tribanders, the X6 and X8, which they say will be available in limited
quantities for July 1997 delivery. They seem to be "log cell" driven
element designs, with no trap reflectors and trapped directors..
But that's not the reason I raise the subject. As a volunteer counsel, I
found several interesting things in the spec sheets.
1. The photos, upon close examination with a magnifying glass, seem to
have been retouched by computer to make it possible to see the elements.
If I were in front of a zoning board, I might point out that these
antennas are so hard to see that retouching was deemed necessary by the
manufacturer to avoid being unable to see the elements in their publicity
photo.
2. The patterns are shown at a height of one wavelength at 20 meters.
Again, in front of a building inspector or zoning board, I would argue
that one wavelength (66-68 feet) is NOT "high," but rather "a height
chosen as typical." As a service to ham radio, I hope that Cushcraft
will choose to include a footnote: "Height of one wavelength chosen as
a minimum for optimum performance at 20 M." I am forwarding a copy of
this suggestion to them.
3. The X8 is specified at a maximum wind survival of >100 mph, with a
1.25 safety factor. My town requires 86.6 mph (30 psf) and no safety
factor is specified in the MA building code. However, as a way to
frustrate hams who wish to put up antennas, some towns are now getting
cute about requiring higher windspeeds. For example, I recently ran into
a situation where Rohn's 86.6 mph spec was insufficient. However, Rohn
specifies 86.6 with a safety factor of 3. I would therefore imagine that
it will handle greater winds, if the safety factor goes down to 1.25. A
while back, I asked W1NA (ex-KA1BQ/I8CZW), a structural engineer
specializing in foundations, what safety factor he uses in commercial
work. He replied that with steel in this application he feels
comfortable at 1.25 to 1.5. Thus, I would hope that other antenna
manufacturers would take a hint from the field experience of this
volunteer counsel and specify their antennas in the future at a safety
factor of 1.25, so that we can put the best foot forward to the building
inspector or zoning board.
CQ-Contest relevance statement: Contesters put up the biggest antenna
systems. Therefore we receive the greatest scrutiny from building
inspectors.
Disclaimer: I have no financial interest in, or relationship with,
Cushcraft.
Fred Hopengarten K1VR
617/259-0088
Six Willarch Road
Lincoln, MA 01773-5105
permanent e-mail address: fhopengarten@mba1972.hbs.edu
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