Topband: Re: Feeding the tower

[Richard Zwirko]

 "Andrew Chesnokov" <ua3ab@dateline.ru> wrote:
> Hello, Reflectees.
> So this questions might be a common to reflector, I need advise on how
> to make my tower to radiate on 160.
> 
> Tower #1 is 42m (140 feet) high with 3 el short Yagi (Force12 Mag340N)
> atop it, Another antenna 5m(15feet) above it is 3 el 30m short Yagi
> (Force12 EF330).
> 
> Another tower is 26m(90 feet) high with 6 el 20m and 6 el 15m Yagis atop
> it. May be this is a better choice?
> 
> What I'd like to have for radials is a kind of elevated radials
> arrangement, 3-6 radials 4-6m high is what I can afford for winter
> season.
> 
> Your input will be appreciated.
> 
> 73, Andy UA3AB

- - -
Andy,
  I'd use the shorter of the two towers. At the K1HTV QTH the tower is
about the same as your smaller one. Mine is about 25 meters high with
about 5 meters of mast on top. It also has large (5el) monoband 20M & 15M
yagis which top load the tower.  The extra metal at the top is enough to
make it look longer than an electrical quarter wave.  The tower is shunt
fed at the 50' point using 3/4" alumininum jacketed CATV cable as the
shunt wire. It is fed at the base with 50 ohm cable with an  Omega match.
All radials (around 16 of them) are on the ground, with most of them a
little less than an 1/8 wavelength long at 160M.

If you use elevated radials on your tower a couple of meters high
the antenna will probably look more like a quarter wave in length
where it could be fed using a Gamma match.  Maybe someone with one 
of the antenna modeling programs could verify the optimum height to
feed it and to connect the elevated radials.

The vertical in use at this QTH is within 3 meters of an apple tree and
within 20 meters of a number of trees which are as tall as the tower.
But even with this less than optimum setting 186 countries have been
worked with 100 Watts, so I can say that this vertical performs very well.
So, I'd recommend using the shorter of your two towers. Hopefully you
will have similar success with it.

73 de Rich - K1HTV
dz@voa.gov