[opendtv] Re: 7" ATSC TV

Dale Kelly wrote:

>> 8-VSB is here to stay, and that suppliers of tuners and
>> demods for ATSC have come up with some very viable products.
>
> Please see the recent FCC test results of eight current model
> "5th Gen" type receivers. None met the minimal A/74
> recommendations: two were close while the others were poor.
> However, none performed nearly well enough for the packed
> spectrum environments existing in most metropolitan areas.
> They are be particularly vulnerable to interference from the
> new unlicensed services which will operate in "white spaces"
> between existing DTV channels.
>
> Given that this performance short coming is related to poor
> RF front end design I know that you won't be surprised at
> the findings since you have recognized and discussed this
> potential problem in the past. It seems to me that to undo
> all of the excellent and costly work done to improve VSB
> processors by using a cheap front end, is unconscionable.

You took the words out of my mouth. I read (quickly) through the report,
and that was my reaction to it also. Strange thing is, this urge to use
cheap tuners is not unique to ATSC. Some time ago I compared A/74 to
Nordig, and A/74 is more stringent in many instances, in terms of tuner
parameters.

> There are a number of off-the-shelf tuner designs which
> would prevent such problems if used and the additional cost
> would be small when manufactured in mass.

It's probably the nature of CE design, to make things just good enough
to be workable for the average joe. But I don't have a lot of faith that
this unlicensed use of white spaces will work without creating lots of
headaches for OTA users. The basic problem is that the unlicensed device
will scan the spectrum, might find in its specific location that a
frequency channel appears free, and then begin radiating. However, the
unlicensed device may be a signal null, and even if low powered, it will
clobber any nearby receiver tuned to that channel. This is painfully
predictable, and no tuner design will solve the problem.

Still, products like the new Samsung STB with ATI Xilleon demod seem to
be quite decent.

Bert
 
 
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