[ANSS-netops] ANSS-netops Digest, Vol 53, Issue 1

[Greg Steiner]

Juan,
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.
Greg Steiner
VLF Designs
On 1/3/2014 6:00 AM, anss-netops-request at geohazards.usgs.gov wrote:
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> Today's Topics:
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>     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 <juanb.lugo at upr.edu>
> To: "anss-netops at geohazards.usgs.gov"
> 	<anss-netops at geohazards.usgs.gov>
> Subject: [ANSS-netops] Seismic Network Communication Systems
> Message-ID:
> 	<CAPP+csSkLFu3ck4VC47WZpgMRzGC7AZgk=YUKTg-0xy9rfxmWg at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"
>
> 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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