I have been experimenting with NVIS on
40 meters. Last weekend I compared an
inverted vee with 60 foot apex, 90 degree
apex angle to an inverted vee with 30 foot
apex, 120 degree apex angle. They were
indistinguishable except for stations within
about 100 miles, in which case the lower
one was a few dB better. I also compared
them to a ground mounted vertical. Although
the vertical was about the same as the vee's
for DX, it totally sucked within 1000 miles.
Many stations that were S9 on the vee's
were inaudible or nearly so on the vertical.
I was expecting some difference, but am
amazed it was so drastic.
I'd like to try the ground wire test, but the
question is what do you use? A wire laying
on the ground, cut for 1/2 wave in free space?
Or recut for correct resonance while laying
on the ground? Or elevate the wire 6 feet and
tune for resonance? Or do you need a whole
grid of wires? The ARRL antenna handbook has
a graph showing that a perfect ground is worth
2 dB or so vs an average one at typical NVIS
angles.
I could put a half wave wire under the antenna
with a relay in the middle of it to "deactivate"
it so I could A/B the system with and without
the wire. Does this sound reasonable? On
the inverted vee's, there are relays that
disconnect the unused vee from the coax
so that it turned into two floating 33 foot
wires. Hopefully, this makes it invisible to
the vee under test, allowing me to use a single
support and feedline without mutual coupling
errors.
BTW, I also tried the vee's on 15 meters (they
loaded up beautifully on the 3rd harmonic).
The 60 foot high vee totally trounced the 30 foot
high one, at least during the weird band
conditions on Sunday.
Rick Karlquist N6RK
richard@karlquist.com
www.n6rk.com
www.karlquist.com
> -----Original Message-----
> From: towertalk-admin@contesting.com
> [mailto:towertalk-admin@contesting.com]On Behalf Of Chris BONDE
> Sent: Wednesday, June 05, 2002 11:03 AM
> To: Al Williams
> Cc: towertalk@contesting.com
> Subject: Re: [Towertalk] NVIS antenna--reflector addition
>
>
> From what I have read, the use of the reflector makes the
> ground part much
> better. There are a few site that explain this. Search on
> NVIS. Does
> EZNEC use a perfect ground? What will your ground be?
>
> I used, long time ago, an end fed antenna. I found that it
> worked better
> just after my wife watered the garden. So I put a wire,
> acctually, the
> rest of the aluminum clothes line wire, under the end feed
> under the gound
> and tied the one end to the grounding rod. Worked better
> than after water
> the garden and lasted longer, even on rainy days.
>
> Just some thoughts.
>
> Chris opr VE7HCB
>
>
>
> At 10:33 AM 2002-06-05 -0700, Al Williams wrote:
> >Our club is planning to have an NVIS antenna for 80m
> >and 40 meters during Field Day. However:
> >
> >The World Radio Books publisher's "Near Vertical Incidence
> >Skywave Communication" book purchased from ARRL
> >contains two articles (by the same author) showing an
> >NVIS wire reflector added to the driven NVIS wire element.
> >
> >Because the ground itself is a reflector, and because
> >EZNEC confirms that adding the reflector is superfluos,
> >we do not think a reflector will help.
> >
> >Agree?
> >
> >k7puc
> >
> >
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>
>
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