On Fri, 23 Jan 2009 17:32:54 -0500, Roger (K8RI) wrote:
>There's a lot of channel switching around, but I think you'll find the
>low VHF including channel 2 will still be widely used and are not going
>away. They certainly are not being reassigned to other services. The
>only reassignments to other services are channels 56 and up.
That's in conflict with what I'm seeing. One piece of info that came to
me in response to my initial question was a report showing DTV to be
quite susceptible to interference from impulse noise and documentation
showing that impulse noise is much stronger on low-band VHF channels (2-
6). Broadcasters were given the option to stick with their low-band
channel for DTV or switch to the higher channel assigned them following
the transition. Most low-band stations have chosen to move to higher
channels, and most mfrs of TV antennas are now building VHF/UHF models
that cover ch 7-52.
To learn what is happening in your area, go to the link below and enter
either your lat/lon coordinates and search for DTV stations within a
radius, or search for the call letters of your local station.
http://www.fcc.gov/fcc-bin/audio/tvq.html
For each station, you'll see listings for LIC (licensed), STA (Special
Temporary Authority), or CP (Construction Permit). TV = Analog, DT =
Digital
I just did a quick check of SF, LAX, NYC, Chicago, Detroit, Kalamazoo.
All of the low-band VHF stations are moving to either high-band VHF or
UHF channels.
>From my study of the FCC website, it looks like some DTV stations will
be using a bit more power post-transition than they were initially.
However -- it has been shown that DTV makes a perfect picture at a
signal to noise ratio of only about 16 dB (and then drops off the cliff
with QSB). That's at least 30 dB better than analog, and is one reason
that broadcasters are typically licensed for about 10dB lower power on
their DTV rigs than an analog TX on the same channel. Also, remember
that VHF and UHF broadcast licenses are ERP, which is TX power plus
antenna gain minus losses in transmission line and antenna combiners.
BTW -- many thanks for all the info folks have sent me. For those
interested in this matter, I'm getting the impression that DTV is less
susceptible than analog on the same channel, and the fact that ch 2-6
are going away will help even more.
By the time the DTV transition is complete, TVI coupled into the input
stage of TV receivers is likely to be almost a thing of the past, and
we'll be left with RFI to the audio/video systems (including those the
TV sets are hooked up to), RFI to telephones, computer speakers, etc.
most of it coupled by pin 1 problems.
73,
Jim K9YC
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