[opendtv] Re: Microtune MT2130 Tuner

  • From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Wed, 6 Dec 2006 13:15:01 -0500

John Shutt wrote:

> Unlike most of my previous posts, I did not mention the
> "D" word in my last one.
>
> You said a single carrier tuner should be easier to
> implement than a multiple carrier tuner.  To wit:
>
> "So this would imply that for equal spectral efficiency,
> single-carrier modulation schemes are easier for the tuner,
> seems to me."

Easier for successful reception with IM products lurking around. If you
have IM products in the IF stage, they will eat into the C/N margin. So
a system which needs less C/N margin for successful reception, all else
being equal, should be able to withstand somewhat louder IM products.

E.g., if you need 15 dB of C/N margin, the IM products in the tuner can
exist with no problem if they, combined with other noise sources, are at
least 15 dB lower than the signal. If the C/N margin is 18 dB, the IM
distortion combined with other racket would have be to half as powerful
to achieve reception. So with respect to IM distortion alone, the single
carrier scheme should have an easier time of it.

> I replied that the single carrier tuners thus far offered
> commercially do not meet the performance standards of the
> LG prototype.
>
> Since it was the very existence of this LG prototype that
> caused others in our industry, including Sinclair, to
> declare the modulation wars were over, I think it is fair
> to continue to point out that even LG cannot (or will not)
> offer a commercial product that matches that one prototype's
> performance.

Again, you are basing all your thinking on reception in Mark Schubin's
apartment.

Let's say you tried a DVB-T STB cum cheap tuner in Mark's apartment,
with 64-QAM and 1/16 GI and 3/4 FEC, and it failed. Would that make you
conclude that DVB-T is a failure? As long as you haven't tested this
out, I have to conclude you must be extremely skeptical about DVB-T.

It is very likely that receiver manufacturers all over decide that the
RF difficulties in Manhattan can better be solved with placing the
antenna on the window sill, rather than force everyone else to buy a
more expensive tuner just for the sake of antenna-over-TV placement in
certain special circumstances.

Again, assuming the tuner explanation is the correct one.

Bob Miller's mobile experiment is another matter. It was outdoor
reception and it was mobile. Which means more than just tuner issues are
involved now. Now you're adding in dynamic echo tolerance, which has
nothing to do with the tuner. And it was outdoors, which is even better
than placing the antenna on the window sill. And I don't know what
spectral efficiency was set. I would compare that with A-VSB reception,
where you get much more comparable training and adjustable spectral
efficiency. Hey, nothing to do with tuner issues!

Bert
 
 
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