Doug Lung /
06.26.2009 02:25 PM
Possible Vizio DTV Tuner Problem Reported
I received an interesting e-mail from a cable operator doing the right thing and trying to make it easier for subscribers with ClearQAM DTV sets to receive unencrypted programming without a cable box by grouping clear channels together and providing useful PSIP data.

In the communication, he mentioned that he found that the Vizio DTV sets with ClearQAM tuners they tested can't tune in QAM signals lower than 135 MHz or higher than 615 MHz. Analog reception was reported as fine over the entire channel range.

It seems very odd to me that a popular DTV set manufacturer like Vizio would limit their QAM tuning range to such a narrow band, when there is no obvious technical reason. The cable engineer discovered the problem after getting calls that some subscribers who were not seeing all the unencrypted ClearQAM channels. Sets with ClearQAM capability from all other vendors had no problem decoding all the channels being sent in the clear.

I've seen cases where small PSIP errors such as inconsistent data between tables, can cause problems on some DTV converter boxes, but not others. However, I've never heard of a case where PSIP restricted the frequency span of the tuners.

I'm asking readers who have Vizio DTV sets and cable TV (a digital subscription should not be required) to e-mail (dlung@xmtr.com) me if they can receive ClearQAM channels outside the 135 – 615 MHz band. As many cable operators put unencrypted signals at the upper end of the band--above 700 MHz--so it should be easy to see if this is truly a problem with Vizio's tuners.

Please note the tuners don't have a problem receiving all analog and 8-VSB channels. The reported problem is with QAM modulation only. I'll report the results next week.



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1.
Posted by: Brian Smith
Tue, 46-01-2009 07:46 PM Report Comment
Below is the since this article was posted. -Original Message- From: Doug Lung [mailto:dlung@xmtr.com] Sent: Wednesday, July 08, 2009 10:43 PM To: Robert Cc: Ryan; Michael Subject: Re: Vizio and Clear QAMs Hi Robert - Thanks for the detailed reply. I've got a short article in this week's RF Report updating the Vizio situation. One of your subscribers also talked to Ryan, who suggested a different channel clearing process that cleared the bad channels and apparently allowed all the ClearQAM channels to be received. My guess is this cleared out the encrypted channels, allowing more space for the ClearQAM channels. I also heard from readers who had no problem with Vizio sets receiving ClearQAM channels. In every one of these cases, the TV sets displayed the station's major/minor channel numbers exactly the same as the broad major/channel number (i.e. 4.1 showed up as 4.1 or 4.01 on the screen, as did 4.2 and 4.3, etc.). This is what I saw on the LG set at my brother's house in Hagerstown. Did you have a chance to dig into the ATSC A65/C link I sent you? I haven't as I've been on the road working on antenna and mobile DTV projects and with the need to handle corporate email and requests in the evening after I get back from the job site I haven't had much time for personal or second job (TV Technology) emailing. That's why I'm typing this at 1:42 AM on Thursday morning in Washington DC! (My computer is still set on L.A. time, so that's what will display in the timestamp.) Regards... ...Doug Robert Gessner wrote: > Dear Doug: > > I saw your article in TV Technology. I apologize if I sent you on a > wild goose chase about Vizio tuners. I believe I sent you an > about our findings after working with Vizio, but I want to be certain. > Ryan at Vizio was very helpful in finding the > solution to this question. It required a lot of tr




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