[opendtv] Re: VHF vs UHF coverage
- From: "Dale Kelly" <dalekelly@xxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Mon, 25 May 2009 22:23:17 -0700
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-----Original Message-----
From: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx]On
Behalf Of Richard Hollandsworth
Sent: Sunday, May 24, 2009 5:17 PM
To: opendtv@xxxxxxxxxxxxx
Subject: [opendtv] Re: VHF vs UHF coverage
If you remove the sync energy (the primary component of the
video carrier), you no longer have
an analog signal, so I can't comprehend what you think you are
comparing.
My original statement:
The average power of a 5 MW analog transmitter (minus the sync
energy) is somewhat comparable to the average power of an 1 MW 8VSB
transmitter
I was comparing average power levels for those portions of the
transmitted NTSC Analog and 8VSB Digital signals that actually contain video
and audio intelligence:
The transmitted analog signal requires significant peak power
overhead for Sync. Also, a major chunk of the 6 Meg channels bandwidth is
used to accommodate the higher power FM audio carrier (higher than average
video power).
The 8VSB transmitted signal does not have such significant
power overheads. It combines video, audio and sync into one data stream and
with the use of a Data Randomizer, while it can contain peaks, does produce
relatively stable power levels across the channels bandwidth.
(FWIW), Many complex analog production chains utilized
encoded non-composite video systems (no integrated sync pulses). Of course,
video signals generated for wide area distribution and transmission require
the use of a composite format but analog video does exist in the absence of
a composite sync signal.
Since a real analog picture is somewhat more black than white
(to prevent bloom), a "typical"
on-air signal would have a long term PAR of about 4 dB, which
is 3 dB LOWER than DTV.
Hence a 5 MW (peak) analog transmitter would be closer to 2 MW
(long term) average power.
holl_ands
A "real" analog picture does not exist and test patterns are
atypical. Analog program material is dynamic and represents the needs of the
TV programs creator. It varies from very dark to very bright and every thing
between. A darker video requires more transmitter power than does a brighter
video. (which you know but a few others on this list may not)
BTW, I believe the NTSC 2 MW longer term average power figure
seems high, 1.25 to 1.5 MW is likely more accurate.
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