All kinds of good possibilities with 70 feet. Great height for 10-20 m.
Works for 80 m quarterwave slopers. Not bad for 160 meter inverted L. Good
for a 40 m bent vertical dipole array or with a husky mast, 2 elements on 40
at about 80 feet would play quite well.
Gene / W2LU
---- Original Message -----
From: "Drax Felton" <draxfelton@gmail.com>
To: "Steve Dyer" <w1srd@yahoo.com>
Cc: "Jim Thomson" <jim.thom@telus.net>; <towertalk@contesting.com>
Sent: Thursday, August 01, 2013 1:56 PM
Subject: Re: [TowerTalk] How High is enough
When I looked into crank ups it doubled the price to go from 90 to 120 ft
That last 30 feet is mightily expensive compared to the benefit.
Sent from my iPhone
On Aug 1, 2013, at 12:41 PM, Steve Dyer <w1srd@yahoo.com> wrote:
I suspect that's why ~70 feet is the sweet spot for crank-ups. Get's you
a 1/2 wave on 40 and full wave on 20.
The big question is always, what is the incremental gain for the $$
spent/extra effort over a baseline.
73,
Steve
________________________________
From: Jim Thomson <jim.thom@telus.net>
To: towertalk@contesting.com
Sent: Thursday, August 1, 2013 8:36 AM
Subject: Re: [TowerTalk] How High is enough
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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