The ground is a reflector, but it is a lossy reflector.
Best 75 degree numbers I can get for a dipole using earth as reflector
are around 6 or 7 dbi.
I'm not sure what figures you were using for an NVIS antenna, but try
this out (7.025 MHz)
Upper wire = 67.5 feet long, 47.7 feet high
Lower wire = 68.4 feet long, 7.4 feet high
I get 11 dbi at 75 degrees with 11.4 dbi straight up.
The maximum NVIS signal I can get for a single wire = 67.3 feet long,
14.3 feet high. which is just under 8 dbi straight up.
That's 3 1/2 db extra signal from the reflector, unless you consider
3.5 db superfluous.
And I suspect you didn't have the program which would search out the
maximum for the single wire NVIS
The two wire is a very doable 40 meter NVIS antenna.
73, Guy.
----- Original Message -----
From: "Al Williams" <alwilliams@olywa.net>
To: <towertalk@contesting.com>
Cc: <ead@arrl.org>
Sent: Wednesday, June 05, 2002 1:33 PM
Subject: [Towertalk] NVIS antenna--reflector addition
> 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
>
>
> _______________________________________________
> Towertalk mailing list
> Towertalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
|