[opendtv] Re: Zoran, Thomson team on digital TV reference design

  • From: Richard Hollandsworth <holl_ands@xxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Mon, 28 Nov 2005 16:46:37 -0800 (PST)

Have you read A/74???  It's a bunch of Guidelines....with few real "spec" 
requirements.  It is more of a test description, rather than PASS/FAIL test 
criteria.
   
  It "suggests" some multipath performance profiles for static pre-echo and 
post-echo with varying Desired to Echo ratio.  The text only "suggests" a 
"typical" performance range of  -10 to + 40 usec, which is shown in Fig 4.3 for 
D/E > 6 dB.  The so-called "zero echo" (<1 dB) case is limited to 0 to 5 usec 
post-echo and the next step up (< 2 dB) case only covers -5 to +10 usec.
   
  Larger values for pre-echo and post-echo are also shown on the chart, with 
increasing ratios for tolerated D/E.  But it appears that these are outside the 
"suggested" range.  So when a manufacturer claims that they "meet" A/74 
Guidelines, which of these test criteria were met???  My guess would be only 
-10 to +40 usec range....
   
  There are a set of Laboratory Test Ensembles, some of which require varying 
the SNR.  However, the PASS/FAIL level is not stipulated in A/74
   
  A/74 also contained some captured Field Ensembles (including those from 
Brazil tests).  Most reported test results stipulate the SNR required to 
operate with minimally acceptable performance for these Field Ensembles.  But 
again, the SNR for PASS/FAIL was not stipulated in A/74....so presumably the 
A/74 test would be conducted without any additional noise insertion.
   
  Refer back to earlier discussion where I pointed out ATI claiming that their 
THEATER ATSC Decoder "meets" A/74, but their submission to SHVERA docket 
clearly shows that they operated error free on only 34 out of 50 Field 
Ensembles....and indeed "special" processing procedures were required to work 
around 9 Field Ensembles that had sample dropouts:
  //www.freelists.org/archives/opendtv/10-2005/msg00285.html
   
  Note that the prototype Zenith and Linx STB's had a variety of problems and 
very clearly did NOT meet those A/74 Guidelines that are somewhat clear, such 
as sensitivity and single signal overload:
  //www.freelists.org/archives/opendtv/08-2005/msg00139.html
                           <holl_ands>
   
  //////////////////////////////////////////
  "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx> wrote:

  Dale Kelly wrote:

> I, like Mark, was very involved in the A74 process.
> Let me be more direct; knowing what we knew at the time,
> the recommended practice was very marginal. Add to that
> the body of information contained in the studies
> published by Charley Rhodes, A74 is simply unsatisfactory.

Sounds like we need an A/74bis, which includes more
discussion of the analog front end itself. If the main
problem now is what Rhodes was analyzing.

Without paying extra special attention to the front end, my
sense is that A/74 gives you receivers which work well in
most cases, but need window placement in the Schubin
apartment.

Still, the unacceptably high sensitivity to pre-echo and to
antenna aim seem to have been solved with A/74.

Perhaps we really need both a tuned RF amp stage and dual
conversion IF, to solve the strong adjacent channel and
IM3 problems simultaneously.

Bert

                
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