Pal Video Tapes

[My names Turkish]

I have a video I want to send to a relative in Australia. I understand that they also use Pal but I was confused by something I saw on the internet. It refered to videos as UK Pal. I presumed that the PAL format is not split down into indivdual countries/regions aswell?

[Irish Steve]

PAL is different even between European countries, but a PAL video should work OK in another PAL region, as the way the data is put on the tape is the same, it's the way it's then sent to the TV that might be different.

The difference is the frequency of the sound part of the transmission, in the UK & ireland PAL-I is used, the parts of Europe that use PAL use PAL-BG. I hit this snag recently with a new DVD recorder, which was built in Europe and shipped to Ireland without the internal setting being changed, which resulted in it recording a picture OK, but no sound.

On the VCR, the sound data is recorded by one head, and the picture data by the rotating helical head, so the "difference" between the PAL settings has been removed by that stage.

So, a tape should be OK. If you took the VCR to another country, there is a very good chance that it would not work correctly in that country.

Hope that helps

[rustle]

Broadcast PAL does, VHS does not.

So don't buy a TV or videoplayer and send it either way, but send videotapes without a problem. :ok:

Edit: Obviously I am answering the first post, not the second ;)

[BEagle]

Australia uses PAL B/G which has the sound carrier 5.5 MHz above the vision carrier, whereas the UK uses PAL I which has the sound carrier 6 MHz above the vision.

As has been said, no problem playing a UK-recorded VHS PAL tape in Oz and vicky-vercky.

More here: http://www.mastervideo.com/videospecs.htm

[Loose rivets]

Thanks from me as well for the link. However, I'm supprised that SECAM is so near to PAL, I had it fixed in my mind that the french enjoyed an 800 odd line picture. Was it ever thus?

[criticalmass]

SECAM is like PAL in that a 64uSec delay-line is used to store a previous line of chroma (colour) information.

In SECAM, that remembered line is used to fill in the next line of colour information, thus halving the amount of chroma information that has to be transmitted and reducing transmitted bandwidth. There are more lines per picture in SECAM than PAL or NTSC, so they had to skimp on chroma bandwidth to preserve bandwidth for the Luminance (black and white) component of the picture.

The difference between PAL and SECAM lies in how that stored chroma information is used.

In PAL, the information stored in the delay-line is used to compare to the next line, and is able to substantially cancel any gross phase-errors in chroma information that inevitably arise from the vestigial sideband transmission techniques used for terrestrial TV brroadcasting.

In this manner, PAL TV receivers give very accurate rendition of colours without the need for a "Hue" control that used to be fitted to NTSC receivers.

The PAL Chroma signal is actually two components transmitted in one composite signal. Black and white information is called Luminance (abbreviated to Y). There are two colour-difference signals:- Luminace minus red, and Luminance minus blue. There is a third (Luminance minus Green), but if you know Luminance and you know the other two, this third colour difference signal can be mathematically regenerated in the receiver, which is exactly what happens (in a circuit called the PAL Matrix). In transmission, Luminance and two colour-difference signals are transmitted, all squeezed into about 7.5Mhz of bandwidth (in the Aussie PAL system at least).

The amplitude of the chroma signals determines the saturation of the colour, the phase (or timing with respect to a reference colour signal called the colour burst) determines which colour is displayed.

The purpose of the internally-generated colour-burst is to re-synchronise the chroma decoder at the start of each new scan-line, assuring accuracy in colour rendition. It is complex, but it works magnificently.

NTSC was the first colour system, and when it was designed, the engineers knew the principle of a memory holding the colour information from a previous line to compare it to the lext line and cancel phase-errors, but the actual physical device (the 64usec delay-line) didn't exist, making them unable to use the principle in their system.

So they cheated - a bit. They also used two colour-difference signals, but they went about it in a very clever way. Since the colour response of the human eye is very poor in the purple part of the spectrum, they deliberately "tilted" the vectors of the two colour difference signals (which they called I or "in-phase" and Q, the Phase-Quadrature signal which is 90-degrees out of phase with the "I" signal) about 33 degres into the purple part of the spectrum. By doing so, small phase-errors in chroma were hard to notice. When the phase errors were gross, the colours looked crook, to use a good old Aussie term.

NTSC receivers today seem to have done away with the "Hue" control, but if you were watching NTSC and the faces appeared grey, you went and tweaked the "Hue" control until the faces were a more pleasing pink, or whatever you wanted.

Of course, with digital terrestrial broadcasts, all this is now old-hat, but in its day it was a great technological achievement.

In TV broadcasting PAL jokingly stands for "Perfection At Last", NTSC stands for "Never Twice the Same Colour" and SECAM stands for "System Essentially Contrary to American Methodology". (This may explain why the Russians adopted it!) TYhere is a small grain of truth in these jokes actually.

In Argentina they use PAL-M...unique to that country. An Argentinian engineer I spoke to said it stood for "Pay A Little More" because all their sets seemed to cost more.

Hope this helps.

[Loose rivets]

Thanks for that.

Aaaah, the memories come flooding back. A quick reminisce for thems interested in these things.

I quit my C&G radio and T/V in the black and white days, to start the CPL, but a chance accident with a Sony broadcast quality camera renewed my interest many years later.

A BVP200 was dropped some 18 feet onto concrete, and when the insurance company had coughed up, I was given the bits. It stayed in a box for a year or so, until one night I had one of those epiphinal type moments. Somehow I knew that I could fix it.

The case was die-cast and ruined, but duct tape kept it together enough to hold the mother board and around 6 daughter boards in place. The half silvered prism had set screws that were bent due to the impact, yet the tubes had survived!! ( 90 degrees looking at the prism.) After some hours of neuro-surgery, all I had left was one minute L,, its wires torn right down to the windings. There was nowhere for it to go. At last I opened up the box surrounding the colour tube and there L9 was marked, with two holes. More detailed fiddling, and at 05:00 hrs, a picture of my pilot's watch filling the 27" screen. However, all the colours were bunched up into one corner.

Half an hour on a lathe, and some more fiddling, and everything was registered...I couldn't believe it.

The cost of having a case made was prohibitive, our airframe dept threw in the towel as soon as they saw it. At last I phoned Sony. I guy I recall well said no, there were no spare cases, but since this was last year's model, he had one complete camera that was going into the crusher tomorrow. I begged the case from him but he said I could have the camera for a grand. The lens was worth many times that alone. I had driven the hundred miles to his office by 08:00

I just don't know why I said it, but I asked I there was any way he could sweeten the deal. He said that there was a Camera control unit, out on loan somewhere, and if I could locate it, I could have it. By the most extraordinary chance, I had heard someone mention that Stanmore Video had such a unit and I phoned the boss. He said get Sony to telex him, and send him a tenner for the carriage, and it was mine. I did, and it was. It was worth about a years salary for most folk then.

If only I had DVD s then. Even so some of my home movies were pretty nifty but degraded by going onto VHS tape. Still, the lot sold to an Ealing Studios work shop, and the proceeds gave me my wages for the next year...which was just as well cos I spent about that time out of work.

[My names Turkish]

Thanks for the replies chaps, much obliged.