Fw: [Milsurplus] What is NVIS?

[windy10605 at juno.com]

Very interesting.....  I have an 18ft military multisection antenna on my
pickup which I operate on HF (80m and 40m) in the down position while
driving and in the up position when needed (no spring). I thought an 18ft
whip, curving over the cab, would be better than an 8ft whip vertical
whip blowing in the wind. Didn't know about NVIS.

73 Kees K5BCQ


--------- Forwarded message ----------
From: Brooke Clarke <brooke at pacific.net>
To: milsurplus at mailman.qth.net
Date: Mon, 31 Jan 2005 10:39:12 -0800
Subject: [Milsurplus] What is NVIS?
Message-ID: <41FE7B50.2050901 at pacific.net>
References: <20050131051806.49708859C94 at mailman.qth.net>

Hi Robert:

NVIS is an acronym that stands for Near Vertical Incidence Skywave.  I
think the term came about during the Vietnam era, although the mode has
always been there.

HF antennas, like a 1/4 wave whip, have a pattern where most of the
energy is radiated at low angels.  For HF the coverage is good out to
maybe 90 miles, then there is a "skip zone" that may be many hundreds of
miles where there's no signal, then the first bounce from the ionosphere,
conditions permitting, allows reception.

If the antenna sends the energy nearly straight up (
Near Vertical Incidence) and the frequency is low enough, then it is
reflected back down. The coverage is continuos from the transmitter site
out many many hundreds of miles and does not require much power.  From
Northern California I can work all of the state and Eastward a few
states, but not anywhere near the Mississippi or East of there.  This
frequency has many factors that cause it to change like time of day,
location, etc.  To see an almost real time map have a look at: 
http://www.spacew.com/www/fof2.html - world map
or
http://www.w0ipl.com/ECom/NVIS/NVISprop.htm - localized to a single
continent.  The North America map at 10 am today is showing frequencies
between 3 and 8 MHz.  This mode does not work at 30 Mhz.

73,

Brooke Clarke, N6GCE

-- 
w/Java http://www.PRC68.com
w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
http://www.precisionclock.com

>Date: Sun, 30 Jan 2005 23:13:33 EST
>From: WA5CAB at cs.com
>Subject: Re: [Milsurplus] tank radio skip?
>To: milsurplus at mailman.qth.net
>Message-ID: <c1.50f4c1de.2f2f0a6d at cs.com>
>Content-Type: text/plain; charset="US-ASCII"
>
>Group,
>
>What's "NVIS"?  
>
>In a message dated 1/30/2005 7:49:45 PM Central Standard Time, 
>kargo_cult at msn.com writes: 
>  
>
>>>A vertical antenna makes a very bad NVIS antenna.  I suspect the
antenna 
>>>is indeed a NVIS antenna.
>>>
>>>      
>>>
>
>Robert Downs - Houston
><http://www.wa5cab.com> (Web Store)
><wa5cab at cs.com> (Primary email)
><wa5cab at houston.rr.com> (Backup email)
>
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