[TowerTalk] NVIS Placement & Beam Separation

[David Colburn]

Al:

   Thanks for your comments!  I visited L.B. Cebik, W4RNL's
site http://www.cebik.com/ and he appears to recommend .2 wl
up (35 feet for 80 meters).

   I was interested to visit
http://www.ci.san-jose.ca.us/oes/races/hfradio.htm
again because I think that is where I got the idea that a real low (8 feet
above grade) NVIS would work well ... think I should have interpreted
it as "will function", not necessarily "well" compared to 20 feet up on
their
test frequency of 40m.  ;-)

- Thanks! & 73, DavidC  K1YP in Hudson, FL

************************************************************************

> Back to this posting--I just spent about 30 minutes with EZNEC modeling
the
> subject NVIS (i.e. 150' each side at 8') at 3510khz.  Naturally the major
> lobe was
> straight up, but I was surprised to find considerable variance in strength
> with
> changing the length of the antenna.  A change from +- 150' to +-250
resulted
> in a 20db difference in signal level.  I used a good ground for the
> model--not perfect.
>
> Also NVIS articles suggest optimum heights between .1 and .2 wavelength
with
> the gain dropping off pretty sharply below .1 wavelength.
>
> 73 k7puc

> >NVIS QUESTION:
> >
> >I am about to run a 300 foot NVIS Doublet (fed with 450 open line).
> >
> >The NVIS would run at 8 feet (above grade) atop wooden fence posts.
> >The utility lines are about 30 feet up.
> >
> >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  (Electric 150ft long, 30ft high)
>
>...........................................................................
> .
> >......  (CATV 150ft long, 30ft high)
> >---------------------------  (Phone 75ft long, 30ft high)
> >
> >
> >
> >````````````````````````````````````````````````````````````````````
> >(Doublet 300ft long, 8 ft high)
> >
> >Should I have any concerns about running parallel with the power and
phone
> >lines at this spacing?
> >
> >(Note: The CATV line is unused and sags some at points, the electric
power
> >cable
> >sags much less.)
> >
> >********************************************************************



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