[opendtv] Re: It's Not Just The Antenna

  • From: "John Willkie" <johnwillkie@xxxxxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Tue, 23 Dec 2008 11:34:09 -0800

I'm not sure what that means, Barry.  Indeed, having sub-channels can rob
performance of both channels if the bit-budget exceeds 19.39 mb/second. If
somebody is telling you this, they basically don't know what they are
talking about, since having null packets to spare is a good thing.


However, it's important to know what is happening.  


Dan installed an external antenna and experienced macroblocking and some
lockups at channel changes.


Given his conditions, he might try to insert a 3- or 6-dB l- or t-pad into
his antenna line and see if too much power is the problem.  It usually is.


Lockups at channel changes could be cause by too much power, or could be
caused by bad PSI/PSIP mismatch (some of the middleware stacks in mid and
low cost receivers haven't implemented this properly or in a way that deals
with real-world situations.) It can also be caused by overshooting the bit
budget, in inartfully designed receivers.


A spectrum analyzer might help diagnosing power issues, but a PSI/PSIP
analyzer will help (someone with knowledge) diagnosing any mismatches.


PSI/PSIP problems are still quite common.  And, FCC fines can result; PSIP
and PSI are mandatory, and it's somewhat rare to have everything okay.  I
can safely say that KYES-DT Anchorage Alaska has near-perfect PSIP.  The
"big issue" right now is System Time Table jitter.  The STT should be issued
at least once per 1000 ms.  Every once in a while, it comes out to 1006 ms.
The error isn't cumulative (hence, jitter, not offset) and I am trying and
testing various tweaks to eliminate it.  


John Willkie



De: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx] En
nombre de Barry Brown
Enviado el: Tuesday, December 23, 2008 9:45 AM
Para: opendtv@xxxxxxxxxxxxx
Asunto: [opendtv] Re: It's Not Just The Antenna



On Dec 23, 2008, at 12:23 PM, dan.grimes@xxxxxxxx wrote:

 And one of the sub-channels (NBC 3.2, Weather) doesn't display at all. 


In my area of Virginia, some of the broadcasters maintain sub-channels
without video to preserve the performance on the main DT channel.


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