Are ATSC Tuner Performance Specifications or Comparison Tests Available? - AVS Forum
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post #1 of 24 Old 12-13-2008, 09:58 PM - Thread Starter
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I would like to buy an LCD TV based on the performance of its ATSC tuner as well as it's picture. I've just discovered that there are apparently large differences between brands and perhaps even between models within a brand. The sensitivity and the ability to reject reflected signals are two critical parameters and there may be more. But so far I haven't been able to find any data from the manufacturers or any comparative test results from third parties. I'm hoping that I just haven't found the right places yet and that someone can point me there.

I'm looking for this data because I accidentally discovered that I have widely different OTA reception performance from a $60 DTV converter and a $500 HDTV. Unfortunately, it's the converter that wins hands down. The HDTV is now about 4 months old and it's almost always unwatchable on at least one, usually two, and frequently all four local network affiliate channels. Usually it's due to rapidly fluctuating signal strengths that, up until now, I've blamed on reflections. At times I also get "no signal" or "weak signal" messages on the HDTV that I haven't known what to blame for sure. So far, I've spent a lot of time experimenting with different directional antennas and configurations with little or no improvement. I was about to give up on OTA. But a week ago I connected the DTV converter I had purchased for our analog TVs. Surprise, surprise- IT works great. I now have my OTA antenna signal split and feeding both TV's. The converter and analog TV work great, the HDTV is bad. Unfortunately, it looks like I accidentally bought a converter with a good tuner and a HDTV with a poor one. I'd like to avoid buying another bad one and save others from the same bad experience.

For the record, the converter is a Digital Stream DTX9950 converter and the TV is an AOC Envision L32W761 LCD TV. I have a good directional vhf/uhf antenna with a very good mast-mounted preamplifier mounted on my roof. The directions to the four transmitters are all within 3 degrees. Thanks.
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post #2 of 24 Old 12-13-2008, 10:39 PM
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Welcome to the forum!

Great question. It would be great if there were a third party evaluation. If you go to the URL below, you will see a listing of converter boxes and their ATSC tuners. The channel master 7000 has a great rep for having a sensitive digital tuner. Your box also has a good rep as well as the current LG tuners. Knowing which tuners have a good rep is a start...

http://en.wikipedia.org/wiki/Comparison_of_CECB_units
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post #3 of 24 Old 12-14-2008, 12:44 AM
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If you want the best possible DTV tuner, buy an LG.

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post #4 of 24 Old 12-14-2008, 02:02 AM
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Even if such a data table existed it may still not properly predict the performance in your particular location. What you discovered is that the TV's ATSC tuner is probably 1 to 2 generations behind that in the CECB. From anectodal evidence it seems like the major TV makers are just now (08 models) getting the 6th gen tuners (which the CECBs have) in their TVs. Some lower tier makers are still using older gen tuners. The only way to really tell is to buy the TV and check it out in your place. If it doesn't work as well as a CECB, return it. You may also ask around in the neighborhood (and perhaps your local HDTV thread) to see if other folks have done these comparisons.
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post #5 of 24 Old 12-14-2008, 07:50 AM
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Since your $60 DTV converter outputs only in 480i I am surprised that you get better PQ of true HD broadcasts(those without sid pillers) then with the ATSC tuner in your TV
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post #6 of 24 Old 12-14-2008, 08:13 AM
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A steady picture without breakups in SD usually looks better than no picture or a lot of breakups in HD.
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post #7 of 24 Old 12-14-2008, 08:23 AM
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Quote:
Originally Posted by ken h View Post

if you want the best possible dtv tuner, buy an lg.

+1
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post #8 of 24 Old 12-14-2008, 09:52 AM
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Quote:
Originally Posted by Ken H View Post

If you want the best possible DTV tuner, buy an LG.

I sure wish they'd make another standalone HD tuner. Seems as a small market many OTA viewers (CECB's aside) are getting left out. Maybe after the transition there will be some movement along these fronts.
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post #9 of 24 Old 12-14-2008, 10:00 AM
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I am also one who wishes that the people/organizations who review HDTVs would do some sort of test of the receivers. In general, the HDTVs are tested as if they were HD monitors. The receiver functions are not even mentioned.
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post #10 of 24 Old 12-14-2008, 10:38 AM
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I would not be surprised if one or more vendors announce new stand alone tuners that will accept either OTA ATSC digital or QAM using Tru2Way cable cards at the CES in Vegas early next month.
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post #11 of 24 Old 12-14-2008, 10:40 AM
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Quote:
Originally Posted by Ken H View Post

If you want the best possible DTV tuner, buy an LG.

Absolutely - LG bought Zenith, which was the leading light in the creation of the 8VSB (ATSC) DTV system. To this day LG are considered the "stewards" of ATSC chipset development. In fact LG manufactures the ATSC chipsets for most HDTVs out there on the market, so electronically most ATSC TV tuners are the same. How they usually differ in their ATSC reception is in their software implementation, and in that area LGs are excellent.

If you are looking at models try to find out which generation of ATSC chipset is being used. I would not buy anything older than Generation 5, but I would search for sets with Generation 6 ATSC chipsets. You might have to email or phone the companies to get a direct answer to that question since that info is seldom seen on website specifications.
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post #12 of 24 Old 12-16-2008, 02:26 PM - Thread Starter
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Thanks everyone. It's mighty annoying that these specs aren't published. I'm planning to start a campaign. The first thing I'm going to do is write the manufacturers and request their specs- to see if they give me any. Do any of you know the names of the specific critical specs I should ask for?
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post #13 of 24 Old 12-16-2008, 03:39 PM
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ckbckb, I've got the smaller brother of your AOC, the Envision L26W761, and I bet the guts of both sets are pretty much the same. Had very similar problems on our "flying saucer," pre-amped antenna in the attic once last spring rolled around. Better antennas and no pre-amp solved all issues, so I believe this HDTV is rather susceptible to front-end overload.

Try this experiment: Bypass the pre-amp and power injector and feed unamplified signals directly from the antenna to the L32 (barrel-connector splices are OK, but not the splitter). If things improve, your antenna is fine, but local signals are too strong for the pre-amp you're using, causing overload. The solution would be a lower gain pre-amp -- or maybe none at all.

We're happy with this set. As with a lot of cheapo HDTVs, though, I suspect AOC's designers cut corners knowing that roughly 17 of 20 buyers would connect the tuner to a cable or satellite service. On the other hand, CECB engineers knew that every last converter box would get signals from an antenna, many of them rabbit ears, and so they made sure their tuners would be more robust in the face of overload, multipath interference, weak signals, etc. I've installed a few DTX9950s for older neighbors hereabouts (rabbit-ears users all!), and I have to agree with you that it's got a better tuner than my L26.

Good luck trying to get anything more out of AOC than what's on the spec sheet. I emailed them a couple of times to ask about parameters such as minimum signal-to-noise ratio and minimum sensitivity to achieve digital-signal lock. No answer. I read an FCC paper not too long ago in which they bench-tested a total of about 30 HDTVs and CECBs for comparison. All the specs anyone would want are in there, but naturally, they wouldn't identify anything by brand and model, only by price range (in the case of HDTVs).
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post #14 of 24 Old 12-16-2008, 03:51 PM
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The problem with a receiver specification or even a set of specifications is that there is no perfect design for all conditions. Some parameters can be traded against each other to give equal performance such as conventional channel definition filter shape factor and D/A converter dynamic range. Others work better in one case but worse in another such as the best time constants that allow a digital filter to properly process weak signals with reflections, cause the a stronger signal to be "lost" when the conditions change. A lot of these parameters have been selected using test signals probably both simulated and recorded and are considered to be prioritary so would not be released. Also these would mean little without an understanding of the processing design. This includes just about everyone including me.
That said as experience has been gained newer designs tend to work better than old ones.
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post #15 of 24 Old 12-17-2008, 10:32 AM
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I had a similar situation. And, just returned the Vizio (VO32LFHDTV - 32" 1080p).
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post #16 of 24 Old 12-19-2008, 10:34 AM - Thread Starter
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Quote:
Originally Posted by Don_M View Post

I believe this HDTV is rather susceptible to front-end overload. ... The solution would be a lower gain pre-amp -- or maybe none at all.

Great idea Don! When I read your post, I was sure that was it. It would also explain some other peculiar behavior I've seen. Unfortunately, nope. But the experiment results are interesting. With no amp at all, the Digital Stream converter still worked perfectly fine, no change at all. But ... the AOC went totally dark, "no signal" on every channel.

I've got a technical email exchange going on now with AOC. I'll post when it's finished.
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post #17 of 24 Old 12-19-2008, 01:57 PM
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Yeah, please do. I'd also be interested in whether your L32 has the same software as my L26; if so, any advice they give you should be applicable to my set as well. There is a way to view software version and date in the calibration panel with the following procedure:

1. With the set turned on, run the VOLUME all the way down to zero using the remote.

2. Press the MUTE button.

3. Enter 9-8-7-6 on the numeric keypad.

4. When finished, press EXIT to close the dialog.

If the version is 396-1088, time stamped Sep 11 2007 14:40, it's the same as mine. The panel includes several adjustments, but I just leave those alone as I have absolutely no idea what the labels mean.
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post #18 of 24 Old 12-21-2008, 09:02 AM - Thread Starter
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Quote:
Originally Posted by Don_M View Post


If the version is 396-1088, time stamped Sep 11 2007 14:40, it's the same as mine.

Mine is 396-1120, Dec 17 2007 10:54. PDC (?) ver is 0504 TPV. I'm curious- how did you find the magic formula to get into the factory menu? Clever.
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post #19 of 24 Old 12-21-2008, 11:01 AM
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Originally Posted by ckbckb View Post

How did you find the magic formula to get into the factory menu?

A post on a competing HDTV forum which shall remain nameless.
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post #20 of 24 Old 10-21-2011, 10:17 AM
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I'm trying to find a 22 to 24 inch HDTV with a great tuner (like the Zenith and Insignia CECB converter boxes). Short of buying and returning TVs that don't measure up, is there any way to determine which TVs have great (gen 6) tuners?
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post #21 of 24 Old 10-21-2011, 10:49 AM
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Quote:
Originally Posted by robandjeanne View Post

I'm trying to find a 22 to 24 inch HDTV with a great tuner (like the Zenith and Insignia CECB converter boxes). Short of buying and returning TVs that don't measure up, is there any way to determine which TVs have great (gen 6) tuners?

Not really.

You could try to post questions in the LCD forum for specific units, to see what others have found. Most brand name sets have decent ATSC tuners these days.

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post #22 of 24 Old 10-21-2011, 12:28 PM
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Agreed. Years ago my Sony CRT was HDTV-ready which meant I had to purchase an HD STB. At that time, I bought the LG LST-4200A for OTA reception (it was a gen3 I think) and it worked beautifully. At 60 miles away from the towers reception was always solid except when they were doing tower maintenance. With that in mind, when we bought our first LCD in January, I looked first at LG, and then decided on them for that and other reasons. Reception (with the same antenna) has been perfect. But yeah, I would think that nowadays, most major manufacturers have good ATSC tuners.
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post #23 of 24 Old 10-21-2011, 05:40 PM
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LG owns all the original patents and research from Zenith, who invented the ATSC broadcast modulation standard 8VSB.

Their products have always been at the top of the class for over-the-air Digital TV reception.

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post #24 of 24 Old 10-21-2011, 10:33 PM
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Quote:
Originally Posted by Ken H View Post

LG owns all the original patents and research from Zenith, who invented the ATSC broadcast modulation standard 8VSB.

Their products have always been at the top of the class for over-the-air Digital TV reception.

Thanks. Nice to know that my research years ago paid off and I made the right choice for my current set, then and now.
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