TVs with best reception OTA - Page 3 - Canadian TV, Computing and Home Theatre Forums

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post #31 of 41 (permalink) Old 2017-09-23, 08:50 AM
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So of your 3 TVs, the only one that would be of any use for troubleshooting IMD problems
would be the KDL32R400A, because like I said nearly all consumer devices max out too early to be of any use. The odds of another user here having that exact model TV at their disposal is pretty slim. So IMO it is much cheaper and more convenient to just go out and grab a PC based tuner, such as the 955q, or the hdhomerun will work in a pinch as well.
Especially since the software tools used are free and open source.

We even have several images for the raspberrypi available with all the tools necessary already compiled/installed, so even a linux novice, could just install the image to an sd card, boot up the pi, plug the usb based tuner (955q) in to the pi, and they'd be in business. But that's another discussion..



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post #32 of 41 (permalink) Old 2017-09-23, 12:48 PM
 
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Rabbit. Thanks for the details concerning the Sony TV's. Do the newest Sony TV's still have the same kind of Diagnostic screens that the older Sony's have? If so, I may spring for a new Sony instead. Will just have to wait a bit while I save up some additional funds. The 2010 Sony I had would get a lock on signals at about 14 db on the SNR meter vs. 15 to a hair above that on my current 2010 Samsung.
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post #33 of 41 (permalink) Old 2017-09-23, 12:50 PM
 
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Major Tom. I will consider the tuner for a computer if I believe something for a Mac is going to be good. I don't have a Windows unit, only Mac these days.
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post #34 of 41 (permalink) Old 2017-09-23, 03:36 PM
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Quote:
Originally Posted by majortom View Post
Seems to work for me here, allowing me to aim straight at Grand Island, and still be able to receive a few of the stronger of stations from the distant CN tower, which is some 60 miles or so right in line behind Grand Island Transmitters. Could never do that before adding the extra attenuation, which for me was only about a 6 dB reduction in signal strength across the board. Previously would have to do that by aiming away from Grand Island. Like putting the welders goggles on to watch that solar eclipse...
That's a good example of how to optimize the SFDR of your equipment to match the signal dynamic range at your location. But, if the difference between the strongest signals and the weakest desired signal is too great, the attenuator technique fails because you run out of weak signal. The required SFDR is too great.

As you increase attenuation, the weak signal SNR improves because the noise floor drops faster than the weak signal drops. At first glance, it seems counterintuitive that you can improve the SNR of the weak signal by making it weaker.
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But as holl_ands would say could result in up to 18 dB reduction in Noise (IMD to be specific).
That is not exactly correct. If you are dealing only with IMD, then for every one dB of attenuation, the IMD spurs will drop the noise floor 3 dB, but you are also reducing your weak signal. This gives you a potential net SNR gain of 2 dB, not 3 dB.

I pushed some amplified signals into a CM7777HD preamp to produce IMD.
Code:

CM7777HD#1 Overload Test, LOW Gain Setting

Atten  SONY  Signal Noise*  SigTo  CH33Sig**  CH33Sig***
 dB    SNR   CH 45   CH43   Noise  into #1    out of #1
       dB    dBmV    dBmV    dB     

  0     0     5.0    -6      11     10 dBmV   26 dBmV(-22.8dBm)
  1     0     3.0    -9.8    12.8
  2     0     1.2   -12.2    13.4
  3     0     0.2   -13.8    14.0
  4     0    -1.0   -14.5    13.5
  5     0    -2.0   -15.8    13.8
  6    14    -3.0   -17.0    14.0
  7    15    -4.5   -20.8    16.3
  8    16    -6.0   -22.1    16.1 strongest CH 45 stable signal
  9    16    -7.0   -23.8    16.8
 10    16    -8.0   -25.2    17.2

CH 45 is weakest reliable signal here
* CH 43 is nearby unused channel to measure noise floor
** CM specs say MAX input to preamp is 10 dBmV
*** CM specs say MAX output is 34 dBmV. CH 33 is strongest 
   local signal. It, and 3 other strong channels (16, 29, and 40) 
   cause  the IMD.
I increased the attenuation in 1 dB steps until CH 45 was stable with an SNR on the TV of 16 dB.

As I increased the attenuation, the signal did get weaker, but the interference was reduced more rapidly. This is because the IMD is reduced 3 dB for each 1 dB of the attenuator, making the SNR net gain of 2 dB for each one dB of the attenuator. This is confirmed by the 20 dB drop in the noise for the 10 dB of attenuation.

There isn't a perfect correlation between the attenuator steps and the change in signal readings. This is because my OTA signals aren't as stable as I would like, and the noise floor here will vary because of the local electrical interference. In spite of that, I think the test is still valid.

If you can not measure it, you can not improve it.
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Last edited by rabbit73; 2017-09-23 at 08:23 PM.
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post #35 of 41 (permalink) Old 2017-09-23, 04:05 PM
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Quote:
Originally Posted by majortom View Post
[LEFT]So of your 3 TVs, the only one that would be of any use for troubleshooting IMD problems would be the KDL32R400A, because like I said nearly all consumer devices max out too early to be of any use.
I don't agree with that. When I am inserting attenuation when I suspect IMD, I only watch SNR, which all of my TVs have. I must admit, that I also have my signal level meter attached to the splitter to measure the strength of the weak signal, but even then I am not concerned about the strength of the strong signal because I'm not tuned to it, so the SS scale isn't saying MAX. If I was really concerned about that, I could insert an attenuator to find out how much higher than MAX it was.
Quote:
The odds of another user here having that exact model TV at their disposal is pretty slim.
Yeah, more like close to zero; I've never seen one like that model. The SS indicator is ordinarily derived from the AGC, which has a much smaller operating range than the dynamic range of the tuner. The engineer who designed that SS circuit must have used a RSSI chip instead. For the price of a TV, I got a TV and a signal level meter with one dB steps that matches the ATSC tuner specs from -8 dBm down to dropout.
Quote:
So IMO it is much cheaper and more convenient to just go out and grab a PC based tuner, such as the 955q, or the hdhomerun will work in a pinch as well.
Especially since the software tools used are free and open source.
It would be cheaper, but most users (like me) are not as proficient as you are with software modification, and are unwilling or unable to climb that learning curve.

I wasn't impressed with the software that came with my 850 and 950; I could only get it to work with one out three of my computers.

Viewers, like my wife, remember how easy it was:
Turn TV ON > Select Channel > Adjust Volume > WATCH TV

If you can not measure it, you can not improve it.
Lord Kelvin, 1883

Last edited by rabbit73; 2017-09-23 at 06:01 PM.
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post #36 of 41 (permalink) Old 2017-09-23, 07:04 PM
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Originally Posted by Billiam62 View Post
Rabbit. Thanks for the details concerning the Sony TV's. Do the newest Sony TV's still have the same kind of Diagnostic screens that the older Sony's have?
Probably, but I'm not certain without checking the menu in a set at a store. The smallest size seems to be 40". There are 32" models, but they are multi-system and don't have the right tuner for us. I bought my KDL40R350D in Dec of 2016. It is just a simple non-smart TV. It does have a Diagnostics screen, but I don't think the picture quality is quite as good as my 32" sets. My wife is happy with it because it is larger for our viewing distance and the closed caption lettering is bigger. I see a few left for sale.

There are a lot of good 32" Sony TVs on eBay.

I see a KDL40W650D smart TV at BestBuy, but I don't know what it will do. The manuals for the smart TVs seem to be harder to wade through to find what you want.

I'll try to do a screen shot and calibration of my KDL40R350D.

If you can not measure it, you can not improve it.
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post #37 of 41 (permalink) Old 2017-09-23, 07:46 PM
 
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Just installed the U4000 again but added four feet of height. At 21 feet now. Breakup is gone. In addition I am getting a reasonably good Signal Strength on 2, 7 and 22 (virtual channels) when the antenna is facing the house at 100 degrees. Picture is stable on each channel. Will tweak the system a bit in the weeks ahead. This does seem to confirm that using either the 4 or 8 bay is best at this location. Have the Titan 7777 pre amp in as well and I am not seeing any kind of overload now. The Televes DAT 790 Mix is a good antenna but this is not the right application for it.

I have a puny house and trying to use a 40 inch TV could present issues. Not much space at all. I will see if I can figure out a way to put in something larger than a 32 inch.
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post #38 of 41 (permalink) Old 2017-09-24, 02:43 PM
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Quote:
I have a puny house and trying to use a 40 inch TV could present issues. Not much space at all. I will see if I can figure out a way to put in something larger than a 32 inch.
I see a Sony KDL32W600D smart TV currently for sale at $299. The manual mentions Signal Diagnostic under Customer Support in the Menu.
https://esupport.sony.com/US/p/model...OC=3#/howtoTab

https://esupport.sony.com/US/p/model...ls#/manualsTab

page 32:
https://docs.sony.com/release//Manual_4584787121.pdf

It weighs 11.5 pounds and has a separate AC to DC adapter instead of a built-in power supply.

If you can not measure it, you can not improve it.
Lord Kelvin, 1883

Last edited by rabbit73; 2017-09-24 at 03:06 PM.
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post #39 of 41 (permalink) Old 2017-09-24, 04:38 PM
 
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Thanks. Just checking Craigslist right now. Found a 32 inch KDLBX302 nearby but the reviews on the Tuner seem to be mixed at best. Not on par with the model I had. I may be better off buying a new model because i can return it if the tuner stinks.
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post #40 of 41 (permalink) Old 2017-09-24, 06:17 PM
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One feature about the Sony that I really like, other than the Diagnostics Screen, is the ability to add a channel after a scan, which doesn't delete the previous channels picked up. Very useful if you have a rotator or more than one antenna system.

If you can not measure it, you can not improve it.
Lord Kelvin, 1883
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post #41 of 41 (permalink) Old 2017-09-24, 08:36 PM
 
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Rabbit. Yes, that was a feature in my 2010 Sony too. Great feature for DXing. Can't do that with the Insignia TV's since there is no way to add channels unless you do a complete rescan. LG allows you to add new channels manually without losing existing channels but it is a laborious process. Noted the new Vizio has a similar feature as the Sony. I do use a rotor of course and would not be able to get some of the channels well if I didn't especially out of Dayton. But even with the local Cincinnati stations there are times when I need the rotor.
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