On Mon, 01 Mar 2010 15:42:24 -0600, Dr. Gerald N. Johnson wrote:
>many went back to their VHF channels, more high VHF than low
>but there are a few stations still on the low VHF channels and
running
>digital.
There are VERY FEW broadcasters still using the low VHF channels (2-
6) (most are in the great plains and Michigan). That is by choice --
those originally licensed to Ch 2-6 were given the choice of their
newly assigned channel or a high-band VHF channel. In addition to the
antenna bandwidth issues (which were just as much a factor with
analog TV), the primary reason is IMPULSE NOISE, which is
significantly higher on those low VHF channels, and DTV is quite
susceptible to problems from impulse noise.
W1RH, Chief Engineer for several major TV stations around Sacramento
and formerly CE of WBZ-TV, told me a third reason why VHF is iess
used is that the FCC allocates less power to VHF DTV as compared to
UHF (even taking propagation into account).
You can find the RF channels, antenna locations and heights for all
US TV stations by plugging your lat/long coordinates into the search
window at
http://www.fcc.gov/fcc-bin/audio/tvq.html
I repeat my bottom line -- a low pass filter on a ham transmitter is
NO LONGER IMPORTANT in preventing TVI. The far more common causes of
problems are leaky cable systems, pin 1 problems in receiving
equipment (including assoicated audio and A/V system), and poor
shielding of receiving equipment.
73,
Jim Brown K9YC
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