[opendtv] Re: COFDM and equalization
- From: "John Shutt" <shuttj@xxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 21 Apr 2004 21:16:49 -0400
----- Original Message -----
From: "Doug McDonald" <dtvmcdonald@xxxxxxxxx>
> The REAL penalty in that single anecdotal test
> you mention is that a crappy 8-VSB receiver was used.
Doug, we have at our station the latest commercially available Zenith and
Samsung 8-VSB receivers, and neither one of them could duplicate the
demonstration that Mark Aitken performed at those July 2000 hearings. He
held a Radio Shack single bowtie antenna connected by a long wire to a COFDM
receiver, and walked from the back of the room to the front witness table
without losing lock once. Neither our Samsung or our Zenith receivers can
even tolerate anyone walking near the indoor antenna without losing lock,
let alone trying to pick it up and move it.
> You keep mentioning anecdotal tests, and never
> the TRULY SYSTEMATIC grid-based ones ... THAT WENT
> ALL THE WAY OUT TO THE FAR FIELD, which 8-VSB
> always won.
The 1999 Baltimore tests included far field tests, and there was no
measurable difference in performance between the two, with the exception
that 8-VSB had a narrower angle of acceptance for it's antenna orientation
to the transmit antenna.
> This includes both Brazil and Australia,
> by the way ... remember that the Aussies did an
> incorrect scaling of 8-VSB from 6 to 7 MHZ, and
> their mistake is still repeated over and over,
> even by the BBC.
Including those tests conducted by the MSTV using a COFDM modulation
monitor? Even that crippled unit outperformed 8-VSB with simple antenna
outdoors at 6 ft., where the front end of the modulation monitor was least
likely to be overloaded.
http://www.dtg.org.uk/news/archive/mstv.pdf
It is time to declare that all future tests of "next generation" 8-VSB
chipsets be conducted in a Sinclair-like by side test with COFDM. Same
transmitter, Same antenna, Same peak power available from that transmitter
(a handicap for COFDM) and only the exciters change. What 8-VSB receiver
manufacturer or chip maker would take on such a comparison? NONE!
A newest generation COFDM receiver will still blow away the performance of
any miracle chipped 8-VSB receiver in all real world reception conditions.
I would even bet that the original 1998 vintage Nokia receiver used in the
Sinclair Baltimore tests, with it hacked front end modified for 6 MHz
channels, would still outperform any 8-VSB receiver on the market today.
It has been 5 years since Baltimore, and in spite of promises and measurable
advances, 8-VSB still is nowhere near the real world performance of COFDM.
But even more alarming is the fact that ATSC is nowhere near achieving the
sophistication and flexibility of DVB-T.
John Shutt
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