On 10/12/2015 12:21 PM, n8de@thepoint.net wrote:
> Many have previously noted that the lack of a good radial system
> produces 'too high' a radiation angle ...
Lack of a good radial system only causes the low angle performance
to suffer while typically not impacting the high angle performance
as much.
For "close in" stations - even NVIS - one is better served putting a
horizontal antenna between 1/4 and 3/8 wave above ground and making
the "ground" as good as possible. Then 1/4 to 3/8 wave height is
the point at which the first lobe is the strongest (only) lobe and
ground losses decrease (efficiency increases) with height. Going
above 3/8 wave will result in two lobes with a greater share of the
radiation in the lower angle lobe - as long as one is talking about
a dipole. Using a directional antenna (e.g. yagi) will attenuate the
high angle lobe due because the directional antenna reduces the
radiation straight up/down to start with.
The low NVIS antennas have become so popular because it is much
easier to erect a single 18 - 25 foot high center support than to
put up an 80 foot center support and two 50 foot high end supports.
The higher antenna will outperform the low antenna on all paths and
all conditions due to the significant ground losses of the lower
antenna (approaching 10 dB with poor soils).
73,
... Joe, W4TV
On 10/12/2015 12:21 PM, n8de@thepoint.net wrote:
I haven't read all the responses to this original question.
My suggestion is: put up a 1/4 wave vertical for the band of interest,
but DO NOT put in an efficient radial system.
Many have previously noted that the lack of a good radial system
produces 'too high' a radiation angle ... seems perfect for the stated
purpose.
73,
Don
N8DE
Quoting Stephen Davis <sdavis@davisrf.com>:
I was indicating what my actual results are, regardless of what
software indicates. Also, if I had looked at software first, I
might still have done the NIVIS based on other practical experience
noted by others in the research I did. Lastly, without software or
others' experience, I still would have tried because my high water
table (in the ground) is 2 - 2.5 ft below grade for a few months in
late winter to spring, and otherwise right about 5.5 ft below grade
(tested when required by town for building an addition, we are on
wells and septics thus the requirement.) I only wish I had a way to
add salt to the water HI.
Hey, it works well for me, maybe not well for others and I don't
disagree with Jim's assessment of the software results. And again,
it is so easy to erect that maybe worth a try where you are.
Steve K1PEK
On Oct 12, 2015, at 12:00 PM, towertalk-request@contesting.com wrote:
Today's Topics:
1. Re: Omnidirectional antenna for domestic contests. TowerTalk
Digest, Vol 154, Issue 16 (Al Kozakiewicz)
----------------------------------------------------------------------
Message: 1
Date: Mon, 12 Oct 2015 14:15:42 +0000
From: Al Kozakiewicz <akozak@hourglass.com>
To: "towertalk@contesting.com" <towertalk@contesting.com>
Subject: Re: [TowerTalk] Omnidirectional antenna for domestic
contests. TowerTalk Digest, Vol 154, Issue 16
Message-ID: <1444659342663.92755@hourglass.com>
Content-Type: text/plain; charset="iso-8859-1"
I'll see your argumentum ab auctoritate and raise you a post hoc
ergo propter hoc and a misleading vividness.
Inefficient wasn't the criteria. Omnidirectionality was. I have an
80 meter inverted V hung from the peak of a one story segment of my
house. The peak is maybe at 16 or 20 feet.
Compared to my very narrow banded vertical, it does quite well
during November Sweepstakes, which is the only time it is used. The
horrific loss makes it quite broad banded which I compensate for by
running 1500 watts 8-)
I'd call the results "good" if by results we're talking about QSOs
in a contest. On the other hand, if by results you mean ERP at
various radiation angles, probably not so much.
Al
AB2ZY
________________________________________
From: TowerTalk <towertalk-bounces@contesting.com> on behalf of Jim
Brown <jim@audiosystemsgroup.com>
Sent: Sunday, October 11, 2015 4:08 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Omnidirectional antenna for domestic
contests. TowerTalk Digest, Vol 154, Issue 16
On Sun,10/11/2015 12:06 PM, Stephen Davis wrote:
A very easy to put up, with good results to a distance of 400 miles
(at least from here in MA) , omni directional , is a NIVIS.
This is VERY wrong. See http://k9yc.com/VertOrHorizontal-Slides.pdf The
major characteristic of the very low dipole you describe is poor
efficiency at all vertical angles. The polar plot done by modeling
software makes it LOOK like its good at high angles, but it isn't --
most of the TX power is lost in the earth.
73, Jim K9YC
73, Jim K9YC
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