[TowerTalk] How High is enough

[Steve Dyer]

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 at telus.net>
To: towertalk at 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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