Jim,
Are you really measuring what DXers are really after when comparing vertical
antennas at different heights above ground and ground mounted.?
A DXer is really interested in the signal that leaves and arrives at the
antenna at angles varying from 5 degrees or so and higher above the horizon.
- and in the case of 40 and 80 metres, quite high angles of arrival and
departure.
Surely what is really required is for the measurements to be taken at an
angle above the horizon, such as a distant hill far enough away to be out of
the Fresnel zone and high enough to be looking at the signal above the
horizon.
Measuring a vertical at another location 5 miles away, but at the same
relative height is really measuring the ability of the vertical antenna to
couple to the ground to produce a vertically polarised ground wave.
I seem to remember some W6 stations doing this sort of measurement at
significant angles above the horizon many years ago, using a nearby mountain
range, but they were evaluating vertically stacked horizontally polarised
arrays, not verticals.
Cheers
Peter VK3QI
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Jim
Brown
Sent: Thursday, 14 November 2013 12:42 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] HF2V Elevated or On Ground
On 11/13/2013 12:48 PM, James Setzler wrote:
> Anyone else have experience with the HF2V mounted up using elevated
> radials versus ground mounted with limited on-ground radials.
Over the summer, I did extensive modeling (NEC) of vertical quarter-wave and
vertical dipole antennas, comparing performance on the ground and at typical
roof heights. A report on that work is on my website in the form of a pdf of
the Power Point for a presentation I did at Pacificon last month.
http://k9yc.com/publish.htm
The executive summary -- for all vertical antenna types and almost all soil
quality, roof mounting outperforms ground mounting. The advantage of roof
mounting is greatest for the poorest soil, varying from as much as 8 dB for
very poor soil to a dB or so for extremely good soil.
I did one series of signal strength measurements on a real antenna -- a 20M
vertical dipole that was first measured with the base at ground level, then
at 10 ft, 20 ft, 30 ft, and 40 ft, and finally with the center on the ground
and the bottom half horizontal (at W6GJB). The difference between 0 ft and
40 ft was 10 dB over a 5 mile path (to a vertical antenna at my QTH). The
soil at his QTH is quite poor.
73, Jim K9YC
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2014.0.4158 / Virus Database: 3629/6817 - Release Date: 11/07/13
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|