ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades TV Troubles

Yes, some models leave out particular sections of circuitry which are not applicable to the intended market. But these days so many parts of the set are in large-scale integrated circuits that the functionality is still there. For example, many modern sets use a multi-mode color decoder IC which supports NTSC, PAL, and SECAM by applying a selection voltage to the appropriate pin, so they just mask out the options that don't want you to see in the menu programming.

Trumpy,
The widescreen sets are a 16:9 aspect ratio. This is actually another thing which is bugging me somewhat. 16:9 mode is fine for watching widescreen movies broadcast in that format, but "regular" TV is 4:3.

So many of these sets have a default setting which stretches the normal 4:3 broadcast picture to fit a 16:9 screen, resulting in lots of fat-faced people and flattened circles and squares. Considering the huge amount of work in the earlier days of TV devoted to obtaining the best linearity and picture geometry possible, I find it ironic that many people now put up with this horrible distortion just to fill the whole screen.

Some don't actually realize that there's an option to switch to 4:3 mode for normal broadcasts.

*An aside: Early British broadcasts were actually 5:4 aspect ratio. The 4:3 ratio was standardized in the late 1940s.

The more expensive Widescreens, e.g. the top of the range Sonys etc do a much nicer job of "stretching" standard broadcasts to widescreen. I'm not 100% sure what goes on but I think they use software to apply the stretching to different parts of the screen so you don't just end up with noticable distortion.

It's often better to leave the TV in switching mode so when it's receiving widescreen it'll fill the screen and when it's normal broadcast it will remain square.

The problem is that applying digital trickery to stretch only parts of the picture still means that some portion of the image has to be grossly distorted.

AS you say, I think it's much better to just have a black space at the left and right of the screen when running in normal 4:3 mode.

Guys,
Check out this link!.
http://www.xtramsn.co.nz/technology/0,,7004-2649263,00.html

I've seen the plasma screens at some of the "Big Box" stores over here. I think a lot of people are getting interested in the idea of a flat-screen on the wall as being a neat idea (and the stuff of futuristic settings only a few years ago!).

I've not been at all impressed with the LCD screens for TV. I find the rendition to be very artificial-looking.

Or have I been conditioned by years of watching a regualr CRT?

cheaper ones produce that harsh look. Also very big screens fed from a digital source can look rather harsh. PAL and CRT often makes colours look more natural thanks to good old fashioned analogue technology

I think duplication of CRT-beam/phosphor image rendition is a ways off yet.

Yeah,
I'd agree with you there, Paul about the Plasma screen TV's.
I went to have a look at a TV reception problem yesterday and found that the signal level on VHF was too low and installed a new Log-Periodic Yagi aerial.
But, long story short, I could'nt get over how strange the picture on this TV screen looked, it looked more like a computer monitor than a TV set.

I had to go back to the house I mentioned at the top of this thread today.

The owner had moved the antenna (as I discovered later!) and rerouted a lot of the cables, running them down trunking to the sockets in the living room.

Then he discovered a problem. The strong RF signals from the VCR, DT (digital terrestrial) box and satellite receiver were fine all around the house. Two of the four off-air analog stations were of acceptable quality but not perfect, one was quite snowy, and the fourth very bad.

That was without the extra pre-amplifier in the attic on the downlead from the UHF roof antenna. When he'd connected the amplifier in line, the whole band was awash with spurious cross-modulation products, rendering even the strong locally-generated RF signals unwatchable. Not surprising considering there was 20dB gain on that amp, then a route through three diplexers in the various boxes, then into a distribution amp with another 16dB gain to each output.

Simple fact is that the signal strengths aren't too bad here, and with a 13-element Yagi array on the roof, a 20db pre-amp is just not necessary! Out it went.....

I checked that the signal coming in off the roof antenna was good -- It was.

Next step was to fix several bad joints -- Again! (Why do some people find it so difficult to install a coax plug properly?)

That improved the signal strengths no end. I then tossed out the cheap and nasty RF patch cords supplied with each box and installed replacements with decent coax cable. By this time I had all four UHF stations to acceptable quality around the house, along with all the VCR, DT, and satellite signals.

All seemed fine, until I'd began checking out the satellite receiver, then switched back to analog UHF and noticed that one station was now very poor again.

Cut a long story short (Too late! ), disconnecting the satellite dish feeder resulted in perfect UHF reception. Turning off LNB power from the receiver gave the same result.

It was only then then the subject of the mvoed antenna came to light, and when I went out and looked up on the roof, there was the UHF antenna sitting about 18 inches away from the LNB on the satellite antenna! Not surprisingly, the UHF antenna was picking up signals from the LNB which were desensitizing the receivers, especially with the 16dB gain provided by the distribution amplifier.

But why had it been all right earlier?

It was only as I was switching back and forth and turning off the LNB power from the satellite receiver menu that the penny dropped.

The universal LNBs used with most modern Sky Digi-boxes in the U.K. are dual-band. A 22kHz command signal sent up the feeder from the receiver switches the local oscillator in the LNB on the dish from low-band to high-band.

A few tests confirmed it: The UHF reception was poor only when the satellite receiver was on a channel which resulted in the LNB being switched to high band.

Moving the UHF antenna away cleared the problem.