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Juan,<br>
There is one solution that will work in the license free bands, but
it is not cheap. The interference you speak of can be reduced or
eliminated by using very high gain antennas. this works better at
2.4Ghz than 900 Mhz because of practical considerations. CERI
operates a 17 mile link over a heavily populated portion of Memphis
TN. normally this type of link would have a 2ft dish on either end
and have plenty of fade margin. When we installed it I put a 6ft
dish on the Memphis end of the link in order to restrict to beam
width of the received signal. this dish has a beamwidth of only a
3-4 degrees, and while pointing considerations require a firm
support for a dish this size (to minimize mis alignment) it has the
effect of removing most of the locally generated interference from
wifi hot spots. In effect our signal is confined to a very narrow
cone that travels about 100 ft above the house tops. rejection of
unwanted signals varies from 30 to 50 dB. There are dishes that have
even narrower beamwidths that uses shrouds around the front of the
dish. these shrouds limit the size of the back lobe of the antenna.
a 6 ft dish is around $1600 and needs to be placed high enough that
its aperature does not include any ground area capable of containing
an interfering signal. Shrouded antennas can be seen on crowded
microwave repeater towers.Parabolic dish antennas can also be
polarized either vertically or horizontally. while this doesn't help
with removing omnidirectional noise sources, it can help with
removing multipath reflectors. as a rule of thumb, use vertical
polarization over large flat reflective sources and horizontal
polarization in cities with tall buildings that tend to be good
vertical reflecting surfaces. hope this helps. Also Happy New Year
to everyone.<br>
Greg Steiner<br>
VLF Designs<br>
<div class="moz-cite-prefix">On 1/3/2014 6:00 AM,
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Today's Topics:
1. Seismic Network Communication Systems (Juan B Lugo Toro)
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Message: 1
Date: Thu, 2 Jan 2014 21:06:39 -0400
From: Juan B Lugo Toro <a class="moz-txt-link-rfc2396E" href="mailto:juanb.lugo@upr.edu"><juanb.lugo@upr.edu></a>
To: <a class="moz-txt-link-rfc2396E" href="mailto:anss-netops@geohazards.usgs.gov">"anss-netops@geohazards.usgs.gov"</a>
<a class="moz-txt-link-rfc2396E" href="mailto:anss-netops@geohazards.usgs.gov"><anss-netops@geohazards.usgs.gov></a>
Subject: [ANSS-netops] Seismic Network Communication Systems
Message-ID:
<a class="moz-txt-link-rfc2396E" href="mailto:CAPP+csSkLFu3ck4VC47WZpgMRzGC7AZgk=YUKTg-0xy9rfxmWg@mail.gmail.com"><CAPP+csSkLFu3ck4VC47WZpgMRzGC7AZgk=YUKTg-0xy9rfxmWg@mail.gmail.com></a>
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First Happy New Year for all !!!!
We remember the old days where our seismic network communication system was
VHF and UHF. It was not so bad as soon as we found a good place to install
repeaters. The FCC assigned us frequencies that no one else can use. But
now we have better digitizers and we need more bandwidth. The problem now
is that we share the frequency spectrum with so many people and I am
talking about the open 900 MHz, and 2.4 GHz. that we are using. At the
beginning of the project you do your homework and test the path everything
was good. After a few months you start receiving interference and your
communications problems start.
I will like to suggest a communication section where we can share data
about problems, experiences and or suggestions of equipment that can be
used.
Thanks
Juan Lugo
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