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Anonymous Poster

New digital TV poor picture quality - any reason?

08/05/2008 6:07 AM

I'm in the UK, I've just bought a Full HD LCD TV and I'm very disappointed with the picture quality when viewing most 'Freeview' digital channels. A few channels are OK but in others the picture is very 'splodgy' rather like a 'paint by numbers' painting. Faces can be indistinct particularly if they are middle distance. In some channels the picture looks slightly out of focus as if the colours (particularly white) are bleeding across. The set is a Panasonic who have a reputation for brilliant clarity so I'm surprised.

Could the picture quality be affected by the quality of the signal from the aerial? I've had to put a signal booster at the TV end of the aerial as the signal quality has always been poor. The aerial is inside the roof space not mounted outside. I'm a Mechanical Engineer not an electronic or communications guy so I'm guessing at the cause. Could poor picture quality be down to some kind of signal distortion rather than a problem with the TV? Would installing cable help?

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Guru
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#1

Re: New digital TV poor picture quality - any reason?

08/05/2008 6:59 AM

The problem is almost certainly one of signal strength. Mounting an antenna inside the loft space cannot help. It is always better to mount a TV antenna outside the building.

Maplin (usual disclaimer) do a simple, inexpensive, box that can be used to assess signal strength and is handy for aligning an already-installed antenna provided safe access can be gained.

The type of cable between antenna and receiver is important, as is the absence of joints and branches in that cable - each one contributes a little to the loss of signal strength at the receiver. Electrical connections at plugs and antennae connections should be "clean, tight and bright". Make sure that the cable is suitable for the antenna impedance and the receiving equipment input impedance, measured in ohms. In simple terms, best results are obtained when all these figures are the same. If one of them is different then some loss of signal may be expected.

The type of antenna is also important. In low-signal-strength area a high-gain antenna is probably the better choice. High-gain antennae are highly directional, and being "off-beam" by a few degrees either vertically or horizontally can seriously weaken the signal at the receiver. Maplins also do outdoor antennae that can be erected by the DIY enthusiast, as do many other suppliers.

As a last resort, the amplifier can continue to be used, though bear in mind it amplifies the background noise as well as the signal, which may give the receiving equipment a harder time in resolving the signal from among the noise.

If access is difficult for DIY antenna installation and adjustment, then it may be that the balance tips in favour of getting an acceptable outdoor antenna installed and aligned by a local professional installer; transferring the safety and liability issues involved with access along with the installation purchase might just be the right thing to do?

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Guru
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#2

Re: New digital TV poor picture quality - any reason?

08/05/2008 9:17 AM

I had exactly the same problem Guest, and rather than paying for someone to fix a rooftop aerial, I switched to cable.

Now the pictures are perfect. I'm sure it would be the same if you switched to sky satellite etc...

John.

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Anonymous Poster
#3

Re: New digital TV poor picture quality - any reason?

08/05/2008 10:38 AM

Thanks for the input.

Due to my lack of knowledge I had thought that a digital signal would somehow retain its clarity so long as the aerial signal was strong enough to be picked up by the digital TV. I now know that there is more to it than that.

Can anyone give me the technical explanation for this?

UK Guest

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Guru
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#4

Re: New digital TV poor picture quality - any reason?

08/05/2008 11:07 AM

I have had similar problems even with cable. While some channels will work others will not.

The digital HD signal uses a much wider bandwidth, requiring better quality and larger-bandwidth wiring, adapters, and splitters. I have had to remove as many splitters as possible to ensure all channels have good quality and reliability.

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Anonymous Poster
#5

Re: New digital TV poor picture quality - any reason?

08/05/2008 11:56 AM

Here in the US a few media pundits (Harry Shearer among them, I think) have enjoyed pointing out that with just a few months go to before the mandated switchover to all-digital broadcasting, researchers are apparently just now discovering (or admitting) that...oops...digital TV transmissions are subject to much more interference issues and have shorter working ranges than the old analog signals. So much for that static-free picture!

In fact, some of the more cyinical conspircy-therory folks have wondered if the whole push to digital wasn't really driven by media companies who plan to exploit the multitude of control-of-use methods & laws that digital media provides.

As for me? I'm sticking to good ol' monaural analog AM radio. It's cheap, doesn't wear makeup and knows how to get around.

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Participant

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#6

Re: New digital TV poor picture quality - any reason?

08/05/2008 11:09 PM

You were actually right at the beginning. The signal is DIGITAL - therefore if the reception is poor, you will get blocks / bits of the screen missing... NOT A LOSS IN PICTURE QUAILTY!! THIS IS THE WHOLE LOGIC BEHIND DIGITAL TV!! It is NOT analog transmission!

Firstly, you have to rememeber that Digital Tv is still compressed using MPEG-2 compression. This is why you see faces at mid distance looking very "smeared" as the MPEG compression has gotten rid of some of the data in order to make the data tansmission smaller. Why do some TV companies compress their images more than others? It's due to bandwith required, and ultimately money to them.

A signal booster or antenna will not change your picture quality one iota if you are not suffering from picture freezing and/or going blocky. To the guys that said a signal booster made his CABLE TV image better, that is correct as cable is ANALOG.

If you watch a full HD movie that the tv stations typically show at 8:30pm, (when they know familes are going to be watching) you will find that the picture quality is MUCH better!

On a side note though, a better set top box will more than likely give a *slightly* better picture, but that is not your problem.

Try my test with the 8:30pm movie and you will see what I mean.

Cheers.

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Anonymous Poster
#12
In reply to #6

Re: New digital TV poor picture quality - any reason?

08/06/2008 7:37 AM

Uh, slick All RF is analog. Just look at it on your handy dandy O'scope. You will seen nice beautiful SINE Waves. Yes Dear Hearts nice smooth sine waves. Gasp perish the thought, but try as they might the EE community still has not managed to kill of all of the analog engineers. This is due to the need for limiting the bandwidth of the signal. a true digital signal is a square wave and has harmonics that extend all the way to infinite frequency. Remember your Fourier series analysis?

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Participant

Join Date: Aug 2008
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#16
In reply to #12

Re: New digital TV poor picture quality - any reason?

08/06/2008 10:50 PM

Ahh maybe you missed what I was saying... just because it is using sine waves doesnt mean its not digital!!!

Eg. Take a sinewave with amplitude 0.1 centered at y=0 for 1 second, then moves it's centre to y=1 for another second. Gasp shock horror! You now have a digital transition from 0 to 1!!!

Please don't patronise me, I work as an electronic and RF engineer and have designed the contactless smartcard interface (ISO1443) that is used in many public transport systems you very possibly have used if you have been a commuter in Singapore, Seattle, Hong Kong, Stockholm, and also as of 9th June 2008, Beijing :)

By the way, we are past Fourier Analysis now... we are onto Wavelets ;)

Cheers.

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Commentator

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#7

Re: New digital TV poor picture quality - any reason?

08/06/2008 2:02 AM

As your signal is digital, your problem cannot be related to reception of the signal, but might have to do with resolution of the screen.

Most HD-ready TV-screens have a resolution of 1366x768 pixels, whereas the signal is configured for another resolution, this can be different from channel to channel. This explains the poor picture quality for some channels or at different times.

The same effect happens on your computer screen. Try changing the resolution setting of your graphics adapter (= signal source). For some resolutions the picture quality of your screen (= signal receiver) will be a lot more blurry than with other resolutions.

The same principle applies for your TV-screen.

Best quality is achieved when buying a full-HD TV set (1920 x 1080 px) and watching full HD-channels. There could be different HD-channels available on a satelite receiver.

I once saw such a TV with full HD-demo (from a DVD), result was awesome. Then the owner changed the signal source to a non-HD-station, the quality difference was enormous.

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#8

Re: New digital TV poor picture quality - any reason?

08/06/2008 2:46 AM

An antenna-mounted amplifier is much the better choice, as it amplifies the signal and not the noise which the lead-in picks up or generates. Power for the amp is delivered through the antenna lead.

It is best to view the picture while the antenna direction (azimuth) is adjusted for the best signal. I used to carry a little 9" B&W set onto the roof, but a purpose-built signal strength meter would also work, and would be easier to hike up the ladder. If the various channels are widely separated by direction, an electric rotator might work for you. In areas where there are hills or other obstructions, the location of the antenna must sometimes be changed, as no amount of twisting and turning the mast will give you a really good signal. You might obtain a topographic map of your area, and locate your house in relation to transmitters for the various channels. If the stations are sufficiently distant that the curvature of the earth is limiting your signal (both VHF and UHF are propagated essentially line-of-sight) then your antenna mast should be taller.

I have done all these things over the course of several years in the name of wholesome, inexpensive family entertainment. You will have to decide for yourself if what television currently provides is worth the trouble and expense. Be careful on the ladder, and good luck!

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Anonymous Poster
#9

Re: New digital TV poor picture quality - any reason?

08/06/2008 3:05 AM

Are you tuned to actual HDTV, not just DTV? Or even SD? You have to take the broadcast programming into account.

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Guru
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#10

Re: New digital TV poor picture quality - any reason?

08/06/2008 3:22 AM

You did not mention exactly what your digital signal source is, if it is DVBT for example, which has a lower resolution than satellite or cable HD signals, that alone can be your problem as many HD TVs show anything other than HD very badly. Tests done by magazines usually point this out for every model tested.

Also, some Sat & Cable digital programs are also not in HD either.

Here in Europe, most Digital TV signals are NOT HD......which is why I will personally, not invest any money yet in a flat screen TV as there is little advantage.

Also, there are still many LCD TVs which have a relatively low contrast and they still cannot display moving objects clearly!!!This is mainly due to the need of backlighting that LCD has, which also uses extra power......

Dolby will be bringing a "fix" out shortly that should improve the contrast ratio, but I doubt that it will get as good as OLED.....nor will it be as eventually cheap either....

In the next couple of years, more TV companies will be selling OLED TVs (only Sony at this time sadly and still small screens) with 1,000,000:1 contrast ratios and due to the competition, much cheaper......no shadows from movement either.

For anyone who has not yet bought a flat screen TV, my best advice is wait a few years till OLED, with its higher contrast, lower running cost, longlife ( in comparison to plasma for example) and brilliant colors with no shadowing is well worth a wait for....

Go and look at the Sony range of OLED screens and compare them to any other TV, except for the size, they leave all others standing. The size problem will also be fixed every shortly.....and by many different companies, so the price will drop dramatically.

If you had mentioned your location on this planet, we on CR4 could have given you even better infos than this.......

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Anonymous Poster
#11

Re: New digital TV poor picture quality - any reason?

08/06/2008 4:36 AM

Thanks for all the input.

To sum up in my simple terms: I need to ensure that my signal receiver and pipe (currently an aerial but probably will be cable in the future) is as good as I can get it in order to get the best picture. Some TV will be poorer quality because of the original source quality.

BTW the TV is a Panasonic TX-37LZD80, Full HD 1080p, Resolution is 1920 x 1080

UK Guest

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Anonymous Poster
#13

Re: New digital TV poor picture quality - any reason?

08/06/2008 9:12 AM

Part of the problem is that there are the same number of pixels in a larger screen area. thus the picture quality looks spotty. The larger the Screen the farther apart the pixels will be creating a lower quality picture.

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Participant

Join Date: Aug 2008
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#14

Re: New digital TV poor picture quality - any reason?

08/06/2008 9:48 AM

Well according to me if you are having a poor signal in your locality there may be this sort of problem. And sometimes the set inside the TV has a problem(the picture tube may vary). Once try mounting it outside.

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Guru

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#15

Re: New digital TV poor picture quality - any reason?

08/06/2008 4:15 PM

Just a thought because I do not know all the signal that might or might not be available.

My main screen interest is DVD movies. My intention is to buy a digital projector, run the DVD's on a PC DVD drive and feed that to the projector. It is also my intention to buy a PC TV card which also then can be fed to the projector.

For sound I already have a 200 watt amplifier and 12" 3 way standing speakers. The amplifier is fed, of course, from the PC.

That seems to be, for me, the least expensive and most flexible way to go allowing for future alterations as different modes become available.

As a bonus, no part of such a system is so complex as to be very expensive should there be equipment failure. What is it folks are paying for large screen TV's? A six hundred dollar projector can turn a whole room wall into a screen or can be the imaging element for rear screen projection.

j.

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Anonymous Poster
#17

Re: New digital TV poor picture quality - any reason?

08/07/2008 12:11 PM

I just got a HD TV also a few months back. plugged it into my cable I noticed that analog signal makes for a worse picture than with a analog TV. I notice on my HD that analog TV looks grainy and blurry whereas if i receive a digital signal the picture is crisp bright and colorful. Just a thought before you go spending a ton of money and time. Make sure you are receiving a digital signal as opposed to an analog one.


~Electron Oasis

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Active Contributor

Join Date: Oct 2007
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#18

Re: New digital TV poor picture quality - any reason?

08/16/2008 1:04 PM

I live in the South East of England in an area not covered by FreeView. To obtain a reliable digital signal I use a masthead amplifier and matching power supply unit. Philex and Televes being a couple of manufacturers. I am also aware that the tuners fitted to flat screen TV's do not seem to be as good as stand alone digital receivers.

I use an aerial mounted in the loft. TV's being Samsung and Toshiba. Even a Sainsbury Red Freeview receiver costing £20 gives a far more reliable reception than the TV tuner.

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Anonymous Poster
#19

Re: New digital TV poor picture quality - any reason?

02/09/2010 11:43 AM

Hi,

I've just purchased a full HD Panasonic TV: TXL37U10B. I was also very surprised at how bad the quality of all the digital channels were!! The analogue picture quality isn't great but it's ok...

On my old tv which was nothing flashy I got a great analogue picture and an even better quality picture through my digital freeview box. But this new t.v. is not a patch on my old one. The digital channels are so pixelated and unclear.

I am now a little confused reading everything above about signal strength and looking at installing new cables and aerials... then reading that all new t.v.'s show a poor digital picture unless it is an HD Programme you are watching or HD Sky, blue-ray etc...

What should I be looking at doing first, installing a new digital aerial which apparently will make no difference to what some of you guys are saying, or do I try something else? Am I going to have the same problem if I take the t.v. back and get a more expensive one??

Any help or advice would be great!!!!!!!

Thanks!

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