wajo
11-28-07, 10:19 AM
I ran across some very interesting, but way too technical, stuff on interference in DTV and loss of tuning... which many people are experiencing with various new SDTV recorders.
For the technically inclined, here's a link to several articles by Charles Rhodes (http://www.tvtechnology.com/pages/s.0072/t.p0001.html), an industry consultant who has been writing and warning about the coming problems with DTV interference.
One key statement by Rhodes might tell the story about our current DTV tuners when he comments on some recent test results ("D/U" = Desired DTV Signal Power/Undesired signal):
"My interpretation of this data is that these receivers [30 ea. 2005-2006 digital TVs] did not meet the ATSC guidelines.
My further comment is that these ATSC guideline D/U ratios for the tested D = –68 dBm do not provide adequate protection to DTV reception, but more on that later."
Many times he mentions how various signal sources can cause DTV interference, adjacent channels, of course, but even "the guy next door who turns on his unlicensed minitransmitter...."
Rhodes' articles are way too technical for most people. Only DTV engineer-types will understand ANY of it. However, Rhodes does point to a March 30, 2007 FCC report on interference rejection testing of thirty (30) 2005/2006 consumer DTV TVs (http://www.fcc.gov/oet/info/documents/reports/DTV_Interference_Rejection_Thresholds-03-30-07.pdf), and he says "It may be the most important technical document from the FCC ever."
Rhodes predicted that the interference problem studied by the FCC will get worse in Feb 2009:
"In other words, the interference can be blamed on poor [TV*] receiver design. Furthermore it is not harmful because no FCC rule has been violated.
This is another new and unanticipated form of interference confronting broadcasters. It will become chronic when unlicensed transmitters become popular. They will become available to the public within 21 months or even less."
To summarize for us humans, the FCC report on 30 consumer DTV TVs makes this statement on pg 15-3:
"The interference rejection test results in this report are presented as signal levels at the threshold of visibility (TOV) of picture degradation—i.e., the point at which picture degradation (in the form of pixilation, image freezes, or dropouts) becomes visible. Increases in interfering signal level above this point result in further degradation—and ultimately complete loss—of the TV picture."
So, the problems we've been having with digital channel loss may well be the "analog interference" mentioned previously by Philips to someone asking about his loss of digital channel tuning in his recorder's NTSC/ATSC/QAM tuner.
Apparently, according to Rhodes, the inteference problems he's been warning about for years are just beginning, and will likely get worse after Feb. 2009, but at least important people are starting to take notice.
For the technically inclined, here's a link to several articles by Charles Rhodes (http://www.tvtechnology.com/pages/s.0072/t.p0001.html), an industry consultant who has been writing and warning about the coming problems with DTV interference.
One key statement by Rhodes might tell the story about our current DTV tuners when he comments on some recent test results ("D/U" = Desired DTV Signal Power/Undesired signal):
"My interpretation of this data is that these receivers [30 ea. 2005-2006 digital TVs] did not meet the ATSC guidelines.
My further comment is that these ATSC guideline D/U ratios for the tested D = –68 dBm do not provide adequate protection to DTV reception, but more on that later."
Many times he mentions how various signal sources can cause DTV interference, adjacent channels, of course, but even "the guy next door who turns on his unlicensed minitransmitter...."
Rhodes' articles are way too technical for most people. Only DTV engineer-types will understand ANY of it. However, Rhodes does point to a March 30, 2007 FCC report on interference rejection testing of thirty (30) 2005/2006 consumer DTV TVs (http://www.fcc.gov/oet/info/documents/reports/DTV_Interference_Rejection_Thresholds-03-30-07.pdf), and he says "It may be the most important technical document from the FCC ever."
Rhodes predicted that the interference problem studied by the FCC will get worse in Feb 2009:
"In other words, the interference can be blamed on poor [TV*] receiver design. Furthermore it is not harmful because no FCC rule has been violated.
This is another new and unanticipated form of interference confronting broadcasters. It will become chronic when unlicensed transmitters become popular. They will become available to the public within 21 months or even less."
To summarize for us humans, the FCC report on 30 consumer DTV TVs makes this statement on pg 15-3:
"The interference rejection test results in this report are presented as signal levels at the threshold of visibility (TOV) of picture degradation—i.e., the point at which picture degradation (in the form of pixilation, image freezes, or dropouts) becomes visible. Increases in interfering signal level above this point result in further degradation—and ultimately complete loss—of the TV picture."
So, the problems we've been having with digital channel loss may well be the "analog interference" mentioned previously by Philips to someone asking about his loss of digital channel tuning in his recorder's NTSC/ATSC/QAM tuner.
Apparently, according to Rhodes, the inteference problems he's been warning about for years are just beginning, and will likely get worse after Feb. 2009, but at least important people are starting to take notice.