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[Antennaware] Re: NVIS -- modeling, mininec vs nec-2 disparity

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Subject: [Antennaware] Re: NVIS -- modeling, mininec vs nec-2 disparity
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Date: Sat, 8 Jun 2002 03:33:03 EDT
In a message dated 6/7/2002 5:28:53 PM Pacific Daylight Time, 
> Subj:Re: [Antennaware] Re: NVIS -- modeling, mininec vs nec-2 disparity 
To: <>
> Date:6/7/2002 5:28:53 PM Pacific Daylight Time
> From:<A HREF="";></A>
> To:<A HREF="";></A>, <A 
> HREF="";></A>, <A 
> HREF="";></A>
> Sent from the Internet 
>      Here is the information about the NVIS Antenna.
> Also this link is excellent:
Bob N3DOK> 
>               Why use an NVIS antenna?
> To work the Skip Zone {out to about 1000 miles}.
> Areas behind obstructions and in dense foliage.
> To hear the near in stations just beyond ground wave range.
> Great for Field Day and contesting as a "Gap Filler" antenna.
> Easy antenna for HF mountain topping and camping trips to get RF out of 
> deep
> canyons.
>                                 Limitations
> Must work frequencies below the Maximum Usable Frequency (MUF).
> This is not a DX antenna.
> Needs to use an antenna tuner for good match.
> Power Limited to about 200 Watts.
> Beverage Mode Losses limit achievable gain.
> ______________________________________________
> Antennaware mailing list
Bob:  Very good summary.  Why the benifits of NVIS antennas have evaded so 
many I don't know.  I really like the horizontal quad loop as a NVIS antenna 
as the Rr is about 3-4 times higher than a low dipole, it's quieter and a 
more balanced pattern than a low dipole.  I plan to run some tests when I get 
moved to SD where I will have 3 sets of 2 horizontal quad loops cut for 
160,80/75&40m over regular ground and then over quad loops on the ground of 
varying length to give good grouind reflections and compare them.  I have 
room for this. The ground or loops act as a reflector and gives 4-6 dB gain 
straight up.  It reflects off the ionosphere and comes back to earth not 
touching any ground on the way to the receiving antenna at first contact.  
The RF gets there with the least loss and no skip zones.  It does great 
during the day also.   At about .1-.15 WL the normal single loop Rr is 
lowered to around 50-75 ohms.  It's a great antenna.
    I have a way using a 80/75m quad loop on 160m to get a 50 ohm load at the 
end of open wire line of a certain length with the same pattern (1/2 wave on 
80/75m-1/4 wave on 160m).  I will write this up for one of the mags soon.  
There is a simple way also to get a very low SWR over the whole160m band (or 
use a 40m quad loop over the whole 80/75m band).  I used the 80/75m loop also 
on 160m 20' high in the late 40's to 1956 in SD, in 1998-99 in SD and the 40m 
quad loop on 80-75m 20' high in Seattle from 1956 to the present.  I call it 
my "Slam Dumk Antnena."  One of my best reports has been been "every time you 
come on with that damn Slam Dunk Antanna, you knock the papers off my table." 
 I have some radials under it also here.  It's a great Net Control Antenna 
    If you operate a 2F, 3F, 4F etc and higher, the pattern is "End Fire" 
with progressively more gain all the way around on each band.  CQ about a 
year ago had a write up of this antenna cut for 160m mounted on 50' poles fed 
with open wire line and a tuner is needed to match the Z at the end of the 
feedline.  For ease of matching with a tuner at its end, I'd suggest an open 
wire feedline 136' long.  An 80m loop is resonant with a low Z on all bands 
above although the Rr does rise.
   It's a great Field Day Antenna.  A suggestion is to use the poles on 
Fooball Fields.  Use a kite with 2 strings to drop a string over the poles 
and use that to pull a rope over them to support the ends of the quad loop.  
It can be a square or triangle but make it horizontal.  71' on a square side 
for 80-6m or 140' on a square side for 160-6m.  Vary the height from 25-100'.
    I'd also like to try the "K7GCO 2X Magnum Model."  It will be cut 284' on 
a square side (full wave on 900 KHz).  On 160m it will have a couple dB gain 
end fire in a clover leaf pattern in free space and the additional and normal 
ground reflection gain on 160m.  Mount this at the top of the poles.  This 
should be a great 160m antenna to cover the US.  Have this mounted on one end 
of the Football Field and the normal 160m quad loop 141' on a square side on 
the other end of the footbal field for dual coverage.
    The 2X model will have even more progressive gain on each higher 
band--all the way around.  A better antenna just doesn't exist.  
   Another wrinkle is to have an all band vertical like the GAP mounted in 
the middle of the loops--for complete coverage.  I've done this.  There is a 
way to feed them together in phase or 90 degrees out for the Turnstile 
affect.  I'll build this in SD again and report on it also.  I was hoping to 
be there for field day this year.   
    A "Semi NVIS Antenna" is a 2 element quad or Raibeam at 30-40' high for 
20-10m.  The vertical pattern is about 50 degrees to the half power points 
and it fills in the higher angle Reflection Factors as a result.  It gives 
optimum coverage 1000-3000 miles at a low cost of $$$ and headaches.  The 
next step up for performance is a 5-8 element beam 75-100' high at many times 
the cost.  k7gco                 

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