Roger Cox wrote:
> I was able to find a Rohn catalog dated Apr 1993 (although the inside cover
> said 1991). It looks like the numbers in the ovals should be used, as
> these specify "allowable projected area (sq. ft.) for round member
> antennas". I only see guying diagrams for 70, 90 and 110 mph, though.
> These tower designs are in accordance with ANSI/EIA-222-E-1991. The TH7DX
> at 11.5 sq. ft. projected area should be useable on guyed Rohn 25G, heights
> 40'-190', at 70 mph (13.0-18.4 sq. ft. allowable). The TH7DX at 11.5 sq.
> ft. is too much, however, for guyed Rohn 25G with 90 mph or 110 mph basic
> wind speed.
>
> The TH7DX at 11.5 sq. ft. projected area should be useable on guyed Rohn
> 45G, heights 40'-180', at 70 mph basic wind speed (11.8-18.8 sq. ft.
> allowable). The TH7DX at 11.5 sq. ft. projected area should also be useable
> on guyed Rohn 45G, heights 40'-160', at 90 mph (11.5-18.0 sq. ft.
> allowable). The TH7DX at 11.5 sq. ft. is too much, however, for guyed Rohn
> 45G with 110 mph basic wind speed (5.8-10.8 sq. ft. allowable).
>
> The above numbers assume "no ice". The basic wind speed for your county is
> listed in EIA/TIA -222-D,E,F. Steve K7LXC is sending me a more recent Rohn
> catalog, so I can see if anything has changed wrt 222-F.
>
> 73 Roger WB0DGF
> Telex Communications, Inc.
> http://www.hy-gain.com
Hi Roger & All,
I agree with all of what Roger said, with one exception. Note 4 on the 45G
guying diagrams says the designs include 8.0 SqFt for side arms. If we aren't
using them, we get to add 8.0 SqFt. to the value in the oval outline. That
would allow the TH7DX at 11.5 SqFt go to 110 Mph basic speed.
The 25G doesn't get to take advantage of this.
Another thought about Roger's listing for the Hygain antennas. Think what you
could put on the tower if you always kept the smaller area pointed at the wind.
The differences are pretty dramatic for everything except the 10M & 6M
antennas!
73, Kurt
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