[opendtv] Re: New Thread: What becomes of Legacy Analog Equipment
- From: "John Willkie" <johnwillkie@xxxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 28 Nov 2007 08:48:30 -0800
Ken;
When you make these measurements are you capturing transport streams? Are
you able to discern if there are dropped packets (continuity_counter
errors)?
I ask this because that's one of the basic criteria that I use to determine
good reception, and it is a level of detail that stb and tv set users cannot
answer.
Once you know you are getting all the packets, the next step is to measure
jitter of the program clock reference. The MPEG-2 specification requires
this to be +/- 500 ns. In the station I'm most familiar with, last time we
measured, pcr jitter was 400,000 ns. Because my customer is experiencing
missing packets, the slew rate bothers me, because 400,000 ns is enough to
slip a packet.
"Some" of the reception issues are actually simple, basic, MPEG-2 errors on
the transmission side. Once you know the transmission is within
specification (8-VSB is more critical here than DVB-T) then you can move on
to receiver issues. Depending on other issues, I know from recent
experience that some receivers are better at rendering out-of-spec
broadcasts than are others.
I suspect that some reception issues are actually signs of stations not
having good enough test equipment, or not measuring the signal at the
appropriate points.
John Willkie
-----Mensaje original-----
De: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx] En
nombre de Hunold, Ken
Enviado el: Wednesday, November 28, 2007 7:32 AM
Para: opendtv@xxxxxxxxxxxxx
Asunto: [opendtv] Re: New Thread: What becomes of Legacy Analog Equipment
Well, "proven" requires a bit more rigorous test, but I have two
different types of off-the-shelf tuners (USB-style, not integrated into
receivers) that I routinely use at my desk in the "canyons" of NYC and
in random locations in hotels in almost two dozen cities, so far. They
work fine. Anecdotally, I would venture a success rate of greater than
90%, and in most of these locations cable TV has been the only
alternative for tolerable NTSC reception.
I recently checked an older, first generation tuner and it still didn't
work any better at my office than it did about seven years ago, so
nothing has "improved" on the transmission side (power, location, etc.)
My guess is that the improved ability to deal with signal reflections is
the reason that these new tuners work so well, but other improvements
might have been put in as well.
I should also add that I don't do these tests just to check the
performance of the 8VSB system. However, I do need to receive the
signals to perform other measurements.
Regards,
Ken Hunold
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