[opendtv] Samsung results
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Fri, 16 Dec 2005 18:45:32 -0500
By the way, since the Samsung measures quite a bit
better than the LG in the CRC tests, I can only guess
either of two reasons why it didn't do as well in
Mark Schubin's apartment as the LG prototype:
1. This test unit wasn't the same one measured by the
CRC, or
2. They also failed to use as good a tuner as
evidently LG must have done.
And on that last point, with the article from Digital
TV Design Line in mind, I will guess that the tuners
of all these "decent but not great" performing units
do not have both the tuned RF amp stage and the "active
image rejection," or perhaps a functionally equivalent
dual IF stage, that the article calls for.
To repeat that important paragraph:
"Ideally the tuner should achieve a minimum image
cancellation across its operation range of 72.5 dB and a
minimum of 68 dB. This is extremely challenging using
standard tracking filter techniques. To meet the requirement
will either compromise the desired channel filter flatness
or require additional tracking filter stages to achieve
additional image suppression. Neither of these are desirable
since the former may render the tuner performance
unacceptable for other distribution means such as analog
terrestrial or cable and the latter will involve additional
design complexity coupled with increased manufacturing cost.
These issues are potentially compounded when aging and
temperature variation effects are considered. A solution
overcoming these disadvantages is to apply active image
cancellation within the tuner by using image reject mixer
technology in the MOPLL section. With this approach it is
feasible to achieve typically 30 dB of image suppression,
which will ease the tuner tracking filter requirement to
42.5 dB. This helps lower manufacturing costs and is also
far less susceptible to environmental aging."
<http://www.digitaltvdesignline.com/howto/showArticle.jhtml?articleID=3D1=
7
3601582>
or
http://tinyurl.com/74ma2
(Sorry, but the tinyurl doesn't seem to work forme. Oh well.)
Bert
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