[mythtv] ATSC uscable channel range?
gary.buhrmaster at gmail.com
Thu Jul 1 20:52:03 UTC 2021
On Thu, Jul 1, 2021 at 8:13 PM Klaas de Waal <klaas.de.waal at gmail.com> wrote:
> I am currently looking at an USA/ATSC cable channel scan done with mythtv-setup and a HDHomeRun tuner.
> The HDHomeRun gives an error on tuning of channels T-7 to T-12 (8.75 to 38.75MHz) and channel 159 (1005MHz).
> According to the WIkipedia https://en.wikipedia.org/wiki/Pan-American_television_frequencies channels T-7 to T-12 are valid but channel 159 does not exist; channel 158 is the highest channel listed.
> Would it be a good idea to remove channels T-7 to T-12 and 159 from the scanning range or are there reasons to keep them?
TTBOMK, no existing cable provider uses the sub-band
T-x channels (there are a lot of good RF and practical
engineering reasons why that part of the spectrum is
considered unusable on real world cable systems), but
specific corporate in-house (not cable provider) uses
may exist (as the HDHR is intended for consumers,
not corporate in-house use, it does not support the
sub-band T-x channels).
AFAIR channel 158 (999MHz) is the highest assigned
TV cable channel.
In practice, even channel 158 is problematic, as the
frequency of 999MHz is often used as a "magic"
value placeholder by many solutions for meaning
that the channel is dynamically assigned (aka SDV),
or IPTV, but there is nothing technically wrong with
a cable system choosing to use it for a QAM channel
(although the number of 1+GHz cable plants is
currently small(*), so the number of systems where
you could even use the 999MHz frequency is small
(all the 1+GHz systems I know of use those higher
frequencies for HSI (typically OFDM due to its far
better efficiency and impairment tolerances).
Again, specific corporate in-house solutions could
broadcast QAM on higher frequencies (a very good
RG-6 cable can transmit with acceptable losses
out to 3 GHz or so, at least for shorter distances),
but those are not a consumer product.
I would think that removing the T-xxx and 159
channel from scanning should impact nearly
no one (and if one has some in-house tuner
and broadcast facility, they can still get that
into their system(s) if they really need to).
(*) Many plants still top out at around 850 or
750MHz (and there are still a few ancient systems
that top out lower) although with ESD, more plants
may be extended to higher frequencies, but that
will be used for HSI, not linear QAM (linear QAM
is mostly considered a legacy product at this
point, and while it will be continued (by many)
for a time, it is only being contracted by most).
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