[SBE] Looking for possible interference when siting a dish --
mlangner at swcp.com
Tue Feb 24 15:31:08 EST 2009
Hello all !!
Potential C-band interference thread --
All good answers.
"Out here in the west" before we site a dish we do an RF survey of the site.
Usually we use a sheet-metal horn and a spare LNB from the shelf hooked into
a spectrum analyzer.
Since this microwave stuff bounces so well, even if you have a company do a
search for terrestrial microwave paths, you likely wouldn't find out about
the bounces off tall buildings, etc.
Another not uncommon C-band interference source impossible to predict -- but
that you can measure -- is certain kinds of radar altimeters from aircraft.
Here in Albuquerque, NM, one station's "look" goes right across the approach
to Albuquerque International Sunport (Airport) for planes landing headed
east. Made us crazy several years ago, since it was so intermittent. But
one day a staff member was listening to the air signal outdoors, and
observed it disappearing as a Southwest Airlines plane was right in line!
A passive C-band filter ahead of the LNB "fixed" the problem.
Still, one TV station here several years ago had no option but to shield its
receive dish. They shielded it, all right! They dug a 10 foot deep hole in
their back parking lot and stuck the dish down in the ground. Poof! No
more TI (terrestrial interference.)
You can also get absorptive panels with with to ring your dish if you have
TI coming in pretty far "off axis."
Last I knew we shared out C-band allocation with Ma Bell and whatever
carriers have come along since.
Moral of our little story? Ya gotta measure it! Then license it to protect
yourself from new potential TI problems as the spectrum continues to get
more and more users.
Good luck !
Mike Langner, CPBE
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