|
World
Analogue Video and Television Standards |
|
Topics discussed:
 Overview of world
TV standards.
Interfacing with
foreign Video and TV equipment.
Playing foreign
video tapes.
Sending video
tapes abroad. |
Introduction.
Analogue TV signals use a bandwidth compression scheme
(invented in 1932) called interlacing. This involves sending
two half-resolution pictures sequentially, and arranging them
so that the lines of one sit half way between the lines of the
other. The two half pictures are called 'fields', and a whole
picture, in keeping with cinema parlance, is called a 'frame'.
A Video standard is usually described by giving the number
of lines per frame, the number of fields per second,
and the method used for encoding the colour information. A full
television standard also needs to state the modulation
polarity used, where the sound channel lies relative to the vision
signal, and what type of sound modulation is used (i.e., AM or
FM). There may also be extensions to the TV standard; for text
or subtitling services, and stereo sound.
Countries which have a 60Hz mains supply (USA, Canada, Japan,
etc) generally use a video standard based on 525 lines, 60 fields/sec.
Countries which have a 50Hz mains supply (Europe, Australia,
Russia, etc) generally use a standard based on 625 lines, 50
fields/sec. There are many variants however, particularly in
the colour encoding method, the sound channel spacing, and the
channels used for transmission. The principal colour encoding
methods are called NTSC, PAL, and SECAM.
For the terrestrial Television standard used in a particular
country, see the World TV Standards
List, then return here for further explanation. |
Basic Monochrome Television
Standards (including
the disappeared).
The table below shows the basic monochrome TV standards on which
all current systems are based. They provide a wonderful example
of how countries and vested interest groups can cooperate to
produce standards - in this case they cooperated so well that
they were able to produce lots of them. |
|
System |
Lines |
Fields /sec |
Video Bandwdth /MHz |
Mod. Polarity |
Sound Channel /MHz |
Sound mod. |
channel width /MHz |
Broadcast
bands |
Main
countries |
|
A |
405 |
50 |
3 |
pos |
-3.5 |
AM |
5 |
VHF bands
I & III |
UK, Eire
obsolete |
|
B |
625 |
50 |
5 |
neg |
+5.5 |
FM |
7 |
VHF |
EU, Aus, NZ |
|
C |
625 |
50 |
5 |
pos |
+5.5 |
AM |
7 |
VHF |
Luxembg
obsolete |
|
D |
625 |
50 |
6 |
neg |
+6.5 |
FM |
8 |
VHF |
Russia, China |
|
E |
819 |
50 |
10 |
pos |
±11.15 |
AM |
14 |
VHF |
France obsolete |
|
F |
819 |
50 |
5 |
pos |
+5.5 |
AM |
7 |
|
France obsolete |
|
G, H |
625 |
50 |
5 |
neg |
+5.5 |
FM |
8 |
UHF |
EU |
|
I |
625 |
50 |
5.5 |
neg |
+6 |
FM |
8 |
UHF |
UK, Eire |
|
K, K' |
625 |
50 |
6 |
neg |
+6.5 |
FM |
8 |
UHF |
Russia |
|
L |
625 |
50 |
6 |
pos |
+6.5 |
AM |
8 |
UHF |
France |
|
M |
525 |
60 * |
4.2 |
neg |
+4.5 |
FM |
6 |
VHF,
UHF |
60Hz America |
|
N |
625 |
50 |
4.2 ** |
neg |
+4.5 |
FM |
6 |
VHF, |
50Hz S America |
* modified to 59.94 fields/sec for
introduction of NTSC colour.
More on TV
standards (EIA 525 and CCIR 625 systems) |
Colour TV standards:
Acronyms:
NTSC = American National Television Systems Committee.
PAL = Phase Alternating Line.
SECAM = Systeme Electronique Couleur Avec Memoire. |
525 Line colour systems:
|
System M |
Subcarrier / MHz |
notes |
|
NTSC |
3.579545* |
N America, Japan |
|
M-PAL |
3.58 |
Brazil only. |
|
NTSC 4.43 |
4.433619 |
Sony hybrid 625 VTR playback of 525 tapes. |
|
Hybrid PAL |
4.433619 |
625 VTR playback of 525 NTSC tapes |
625 Line colour systems:
|
System B-L, N |
Subcarrier / MHz |
notes |
|
PAL |
4.43361875 |
W Europe (not France), M East, Aus, NZ. |
|
N-PAL |
3.58 |
S America - to squeeze into American channels. |
|
SECAM V/H |
FM |
France, Russia, M East. |
|
NTSC-N |
~3.58 |
50Hz countries using American channels. |
|
Hybrid NTSC |
3.579545 |
525 VTR playback of 625 tapes. |
RF Input to TV set or VTR.
In general, if you feed a modern TV set with a signal
of the wrong standard, you will get a monochrome picture provided
that you can tune to the right channel, and the modulation polarity
is correct. 525 line TVs will lock to 625 line signals, and vice
versa, but you may need to adjust the Vertical Hold control (some
TVs have a knob, some need a screwdriver, and if its too modern
to need a V-Hold control, it will probably lock anyway). Most
systems nowadays use negative vision modulation. This is done
so that vehicle ignition interference comes out as black spots,
rather than white spots. France is a notable exception. If the
modulation polarity is wrong, you will get a negative picture
which will only remain stable with critical adjustment of Horizontal
and Vertical hold controls - this is amusing, but not very useful.
The sound channel is the position of the sound carrier relative
to the vision carrier (in MHz). You can tune sound channels independently
using a VHF/UHF scanning receiver (wide band FM required),
but the TV set treats the sound channel as a subcarrier, so you
will get no usable sound from a TV unless the sound channel offset
and modulation type are correct. Camcorder RF modulators often
have a sound system switch (eg., I-G for UK models), so you can
try changing that if there's no sound. Don't forget that you
can use headphones, or plug the camcorder into a Hi-Fi amp if
the TV sound won't work.
Before you can plug an RF modulator into a TV or VTR, the TV
tuner must be able to receive in the band the modulator uses,
and the aerial connector must be of the right type. The Belling-Lee
coaxial connectors used in the UK are not universal, and you
may need a 75-300W adapter. Britain
uses UHF only. Most parts of the world use both VHF and UHF.
Some sparsely populated countries use VHF only, and don't bother
with UHF because the range is too short.
More on
TV broadcast channels.
Video, S-Video and SCART connections.
Direct connection circumvents all of the problems relating to
sound channel, modulation polarity and transmission band, and
gives vastly improved picture quality (especially of S-Video
is used). Unfortunately, such inputs cost money, and may not
be provided on hotel TVs or older sets. Many modern TVs (Sony
and others) can actually work with a variety of 625 and 525 line
colour standards (check the product literature).
Video Tapes.
If you want to send video tapes abroad, or receive tapes from
abroad, your primary interest is the video line standard and
the colour system. Because of the proliferation of TV standards,
it is quite common for people in some parts of the world (esp.
Middle East and S. America), to own multi-standard equipment.
Additionally, if you are prepared to pay for the privilege, it
is possible to buy 625 line VHS VTRs which can playback 525 line
tapes (in colour on a 625 line TV) and vice versa - check the
product specifications.
Standard VHS tapes: You may encounter these recorded as
525-NTSC, 625-PAL, 625-SECAM, and 625-MESECAM. The two SECAM
recording methods are not the same.
S-VHS tapes: These can be recorded either as 525-NTSC
or 625-PAL. There is no SECAM recording format, the S-VHS (and
Hi-8) VTRs used in SECAM countries actually record the signal
as PAL. Don't forget that S-VHS machines also record and play
back standard VHS, and being expensive, are the ones most likely
to have playback facilities for the alternative line standard.
If all else fails, you'll need to take the recording to someone
who owns a TV standards converter. The process of converting
from 59.94 fields/sec 525 lines, to 50 fields/sec 625 lines,
and vice-versa, involves digitising the signal and storing several
frames (or parts thereof); so that complex spatial and temporal
interpolation can be carried out. The quality of the final result
varies according to the sophistication of the interpolation methods
used. Many companies offer standards and format conversion services,
but you must expect some quality loss. |
D.W.K. 2000, 2002 |
