It has been mentioned that if you could only put up 1 tower, that 100 foot
would be ideal.
Why not higher ? I helped with the design of a 190 foot rotatable tower for a
buddy
just south of me. Yagis for 80-6m..including 17+12m..but no 30m. 2 x
Stacked yagis on
15m..and also 40m. 3 yagis used on 20m. All ants pointed in the same
direction at all times.
He is a dxer...not a contester. I designed the LC box for 20m and also 40m.
All 3 x 20m
yagis driven in phase at all times..and ditto with 40m.
On 40m, I designed the BIP-BOP mod, using vac relays built into the 40m LC
box. 40m yagis
at 90 foot and also 180 feet. The BIP-BOP for 40m was a huge disappointment.
Only once on 40m,
during the day, was BOP louder...and that was while listening to a group in
Ore, 280 miles south.
BIP reigns supreme the other 99.9999 % of the time. That’s day or night,
any direction, any time,
and day of the year, short path, long path, local or dx..... for the last 3
years.
I was expecting a lot more from the 40m BIP-BOP box. It was triple checked
too. An electrical half wave
was switched into the bottom yagi for BOP mode.
The LC boxes are simple. Just a shunt C..made from NPO caps on the input,
with a series L made from
copper tubing, then either 2 or 3 paralleled output coax connectors. 50
ohms in and 25 ohms out..on 40m.
50 ohms in and 16.66 ohms out on 20m. Equal length coax to each yagi .
A lot of this tower height argument will depend on available real estate.
City lot or acreage.
In typ city suburbs, homes can be as high as 30 feet. Typ utility poles are
as high as 40 feet, then the
steel support above that, so perhaps 41.5 feet...then the 12.5 – 14.4 kv line
strung between poles at the
41 foot level.
Put the yagi up at 35-40 feet..and imo, you are wasting your time. You are
not even clearing the power lines, trees,
homes on the high side of you etc. Even at 50 feet, you are barely clearly
this stuff. 75 feet is a good compromise
between 50 and 100 feet. When I increased height from 48 ft to 67 ft, the
difference was apples and oranges.
On 20m, a yagi at 100 ft has a huge null at 20 degs. Same yagi at 50 ft has
max gain at 20 degs. Put the same yagi
at 75 ft...and max gain is at 15 deg..and no need for a high-low switching
setup. If 100 ft is too high on 20m,
sure come down a bit..but not down to 50 ft. At least here in the pacific
north west.
Jim VE7RF
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