Notes On The Troubleshooting And Repair Of Television Sets


  31.2) Some questions and answers about TV standards

(Responses from: Steve McKinty: (smckinty@france.sun.com))

    31.2.1) What are the most common TV standards in the world?

NTSC:        National Television Standards Committee
PAL:         Phase Alternate Line
SECAM:       SEquential Couleur Avec Memoire (Sequential colour with memory)

There are other differences though. Strictly they are just different
colour systems, but most countries which use PAL have 625 lines in
a picture and send 25 full pictures/second, most NTSC countries have
525 lines and send 30 full pictures/second (mostly for historical
rather than technical reasons). That complicates things.

    31.2.2) Who devised them, and when? and why? Are they as old as television?

The first serious TV experimenting was done in several countries around
the period 1900-1930, mostly black & white. The BBC started a regular
service in 1936, other countries followed soon after, but since the
technology was developing very rapidly there were always improvements
being made. The BBC started with 405 lines, the US started a service
a couple of years later with 525, by the time other European countries
started the technology allowed 625 lines. France even tried 819 lines.

All those system were black & white, but people wanted to have
colour. During the 1940's much of Europe was at war, and technological
development for entertainment slowed down, but in the US they
were able to continue and devised a colour system which was
compatible with the existing black & white one.

By compatible I mean that a black & white TV got a black & white
picture, a colo(u)r one got a colour picture. No need to make people
throw away their B&W TVs. This system was endorsed by the American
National Television Standards Committee, and was named after it => NTSC.

After the war other countries started to look at colour. NTSC was a
very clever system, but it had some flaws. Engineers in various
countries tried to improve on it, and Telefunken in Germany came up
with a simple modification which improved colour stability. It
was named PAL because they reversed the Phase of the colour signal on
Alternate Lines.

At the same time Henri de France, in France, fixed the same flaw in
a different way. His design (SECAM) needed a memory inside the set
which made it more expensive. PAL gave as good a result, so most
countries opted for that. France stayed with SECAM, possibly because
in the De Gaulle era of the 50's memories of German occupation were
still fresh, and dropping a French system in favour of a German one
would have been unpopular. Rumour has it that the French government
subsidized Thompson to make memory affordable.

Since Britain went PAL, France went SECAM, and the US went NTSC, any
colonies or dependencies of those countries tended to get the same
system. India/Pakistan got PAL, Algeria got SECAM, and since the
US helped rebuild Japan after WW2 it got NTSC, etc.

    31.2.3) What's the difference?

To squeeze a colour signal into the same space as a black & white one,
and stay compatible, the NTSC designers separated the colour and
brightness information. The human eye is less sensitive to colour, so
they were able to reduce the bandwidth of that signal (make it take
up less space in each channel), 'hiding' it at the high-frequency
end of the video. That meant they didn't need to make the channels
bigger, and incompatible.

To do that, they used the fact that you can represent most colours
with a combination of Red, Green and Blue. If you film a scene
with three cameras, one for each colour, then add all the
outputs together you get a black & white image. This signal
is called luminance, usually represented by 'Y'. Mathematically
Y = R + G + B.  (Actually, not all the contributions are equal).

They then transmitted the Y signal just as for a black & white TV,
and also transmitted the R and B in the extra colour signal. B&W TV's
only saw Y, and colour TV's got Y, R and B. Since Y = R + B + G, G can
be obtained as Y - (R+B), so they didn't need to transmit all three.

To get both R and B into one signal, they use a combination of
Phase and Amplitude modulation (think of it as AM and FM at the same
time). Its called quadrature modulation, and works very well, but is
susceptible to phase changes as it passes along cables, etc. If the
signal gets +10 degrees phase change the colour will visibly change,
which is why NTSC TV's have a tint control.

PAL overcomes that by sending R and +B on one line, then R and -B on
the next. That way a +10 phase shift on one line becomes -10 on the next,
and small differences will cancel out. PAL TV's don't need tint controls.
(Some old PAL sets may have a one, however).

SECAM doesn't send both R & B together, it sends R on one line, B on
the next. No fancy modulation, so no phase problems, but you need a
'memory' in the set to save up the signal from the previous line,
since both R & B are required together for processing.

    31.2.4) Why do you need different TVs?

Mostly because of the different numbers of lines. Its quite easy to
make one colour decoder which can cope with all the systems, but
making a TV which can do 625 and 525 lines, 25 and 30 pictures/second,
gets expensive. Consumers shop on price, no-one will buy a SECAM
TV in the USA even if it only costs $20 more, since there aren't
any SECAM channels.

    31.2.5) Why do you need different VCRs? Why can't one VCR record the same "output"?

Some can, but like TVs it costs more to make them adjust. The motor
speed varies with the number of pictures transmitted per second, for
example.   (This is covered in more detail in the document: "Notes on
the Diagnosis and Repair of Video Cassette Recorders".)

    31.2.6) Why did different systems evolve? Is one cheaper? Is one better?

When originally developed, expense was considered based on contemporary
technology.  As noted, politics may have been equally important.

As to which has better quality, its all rather subjective. The
625-line system adopted in Europe has better vertical resolution
than the 525-line US system, but some people find the 50Hz field rate
still produces some flicker. NTSC/PAL/SECAM are all equally capable
of excellent colour reproduction, but under poor signal conditions
NTSC can degrade more quickly.

    31.2.7) Are there other systems besides the ones I've mentioned? Why?

Some others, like MAC where the colour and luminance are completely
separated. That gets rid of interference (ever see the strange
colours which appear on very fine check patterns?) but is more
expensive and really only possible due to modern electronics.

    31.2.8) Are there going to be more or less systems in the future?

That is THE question! There are certainly going to be different
systems, more lines, better sound, etc.

    31.2.9) Is there any way to convert a PAL tape to NTSC or vice versa?

Yes. If the PAL tape has 625 line pictures and the NTSC one has 525 line
then you normally need a computer which can read in one format and
re-adjust things. Not cheap, but becoming cheaper, several companies
offer that sort of service.  Some PAL VCRs can do a half-conversion,
enough to fool most PAL TVs into thinking its got a PAL signal.

    31.2.10) Do they teach this stuff in electrical engineering courses?

Sometimes. Some of it, depends a lot on the course and school.

  31.3) Politically Correct TV Standards

(The following is from: Robert Rolf).

                Used by France and the former Soviet union.
                No tint control. No color control.
                Full socialism. The state knows exactly what color you
                should see, and how strong that color should be.

                Used by Germany & UK, Australia etc.
                No tint control. A color control.
                Partial socialism. The state knows exactly what color you
                should see, but you get a choice as to how strong it can be.

                Used in USA and Canada, Japan etc.
                A tint control, A color control.
                Uncontrolled socialism. The state lets you chose what color you
                see and how strong it can be. They then tax you regardless.

   Just another way of looking at it....

  31.4) Variations on a 'standard' - the PAL system

In the U.S., when PAL is mentioned, it is usually assumed to be 625 line/50 Hz
as used in the UK and man other places.  However, there are several variations
on the PAL system.

(The following from: Ed Ellers 

  31.5) What about PAL sets WITH a tint/hue control?

Here is one for the record books - a Sony PAL TV that really wants to be NTSC!

(From: Tony Duell (ard@p850ug1.demon.co.uk)).

Although this very old Sony set (KV1300) receives PAL signals, it's much
closer to an NTSC set inside. In fact it's one of the strangest PAL decoders
that I have ever seen. As you know, in the PAL system, the phase of one of the
colour signals is inverted on each line, and in the receiver there's a
bistable which switches at half the line rate to re-invert the colour signal
on alternate lines. Well, to avoid a patent, the Sony set only uses (say) the
in-phase colour signal that's received on alternate lines.  For the lines in
between it uses the previous line's colour signal (ignoring the incoming
inverted one), which has been stored in a delay line. 

This approach avoids the main patent on the PAL system. It also means that
this  set doesn't automatically correct for phase errors in the colour
signals - it's almost an NTSC decoder.  Hence the hue control (which is also
on my KV1320UB schematic).  It's just about the only set like that.

  31.6) TV, shortwave, power worldwide

(From: Mark Zenier (mzenier@netcom.com)).

A book, "The World Radio TV Handbook" published by Billboard that covers TV,
along with where all the world's shortwave radio transmitters are, and what
sort of power comes out of the wall plug all around the world.  It has a new
edition each year and costs around $25 to $30.

  31.7) Color television standards worldwide

(The following is from EDMUNDO, Design Engineer Ten-Lab.  This and additional
information are available at: http://www.tenlab.com/format.htm).

We at Ten-Lab have put together the following chart listing countries
and their  corresponding color TV standards. 

We are trying to be as accurate as possible, but we need your feedback to
refine and correct the information. We are doing the best we can in spite
of inherent problems such as:

1) Some of the         literature and charts are contradictory; even some books and 
   manuals contradict each other more than they agree.

2) Many countries have changed their names during the last few years.

3) Some countries have one broadcast TV system, but also receive programs in a 
   different system from beyond their borders. This creates some confusion
   about the format(s) used locally.

COUNTRY                        VHF STANDARD        UHF STANDARD

ALBANIA                        PAL B                PAL G
ALGERIA                        PAL B                PAL G
ANGOLA                        PAL I                        
ARGENTINA                PAL N                PAL N
AUSTRALIA                PAL B                PAL G
AUSTRIA                        PAL B                PAL G
AZORES                        PAL B
BAHAMAS                        NTSC M
BAHRAIN                        PAL B                PAL G
BANGLADESH                PAL B
BARBADOS                NTSC M
BELGIUM                        PAL B                PAL H
BERMUDA                        NTSC M
BOLIVIA                        NTSC M
BOTSWANA                PAL I
BOURKINA FASO                 SECAM K1
BRAZIL                        PAL M                PAL M
BRUNEI                        PAL B
BULGARIA                SECAM D                SECAM K
BURMA                        NTSC M
BURUNDI                        SECAM K1
CAMBODIA                NTSC M
CAMEROON                PAL B                PAL G
CANADA                        NTSC M                NTSC M
CANARY ISLANDS                PAL B
CHAD                        SECAM K1
CHILE                        NTSC M                NTSC M
CHINA                         PAL D                        
COLOMBIA                NTSC M                NTSC M        
COSTA RICA                NTSC M                NTSC M
CUBA                        NTSC M                NTSC M
CYPRUS                        PAL G                PAL G
  CZECH REPUBLIC        PAL                PAL
  SLOVAK REPUBLIC        PAL                PAL
DAHOMEY                        SECAM K1
DENMARK                        PAL B                PAL G
DJIBHOUTI                SECAM B                SECAM G
DOMINICAN REP                NTSC M                NTSC M
ECUADOR                        NTSC M                NTSC M
EGYPT                        SECAM B                SECAM G
EL SALVADOR                NTSC M                NTSC M
ETHIOPIA                PAL B                PAL G
FIJI                        PAL B
FINLAND                        PAL B                PAL G
FRANCE                        SECAM L                SECAM L
GABON                        SECAM K1
GAMBIA                         PAL I        
GERMANY                 PAL B                PAL G
GHANA                        PAL B                PAL G
GIBRALTAR                PAL B                PAL H
GREECE                        SECAM/PAL B        SECAM/PAL G
GREENLAND                NTSC M/PAL B
GUADELOUPE                SECAM K1
GUAM                        NTSC M
GUATEMALA                NTSC M                NTSC M
GUANA (FRENCH)                SECAM K1
GUINEA                        PAL K
HONDURAS                NTSC M                NTSC M
HONG KONG                PAL I
HUNGARY                        SECAM D/PAL        SECAM K/PAL
ICELAND                        PAL B                PAL G
INDIA                        PAL B
INDONESIA                PAL B                PAL G
IRAN                        SECAM B                SECAM G
IRAQ                        SECAM B
IRELAND                        PAL I                PAL I
ISRAEL                        PAL B                PAL G
ITALY                        PAL B                PAL G
IVORY COAST                SECAM K1
JAMAICA                        NTSC M
JAPAN                        NTSC M                NTSC M
JORDAN                        PAL B                PAL G
KENYA                        PAL B                PAL G
KOREA NORTH                SECAM D
KOREA SOUTH                NTSC M                NTSC M
KUWAIT                        PAL B
LEBANON                        SECAM B                SECAM G
LIBERIA                        PAL B                PAL H
LIBYA                        SECAM B                SECAM G
LUXEMBOURG                PAL B                PAL G/SECAM L
MADAGASCAR                SECAM K1
MADEIRA                 PAL B
MALAGASY                SECAM K1
MALAWI                        PAL B                PAL G
MALAYSIA                PAL B
MALI                        SECAM K1
MALTA                        PAL B                PAL H
MARTINIQUE                SECAM K1
MAURITANIA                SECAM B
MAURITIUS                SECAM B
MEXICO                        NTSC M                NTSC M
MONACO                        SECAM L
MONGOLIA                SECAM D
MOROCCO                        SECAM B
MOZAMBIQUE                PAL B
NAMIBIA                        PAL I
NEPAL                         PAL B
NETHERLANDS                PAL B                PAL G
NETH. ANTILLES                NTSC M                NTSC M
NEW CALEDONIA                SECAM K1
NEW GUINEA                PAL B                PAL G
NEW ZEALAND                PAL B                PAL G
NICARAGUA                NTSC M                NTSC M
NIGER                        SECAM K1
NIGERIA                        PAL B                PAL G
NORWAY                        PAL B                PAL G
OMAN                        PAL B                PAL G
PAKISTAN                PAL B
PANAMA                        NTSC M                NTSC M
PARAGUAY                PAL N
PERU                        NTSC M                NTSC M
PHILIPPINES                NTSC M                NTSC M
POLAND                        SECAM D/PAL        SECAM K/PAL
PORTUGAL                PAL B                PAL G
PUERTO RICO                NTSC M                NTSC M
QATAR                        PAL B
REUNION                        SECAM K1
RUMANIA                        PAL D                PAL K
RUSSIA                        SECAM D                SECAM K
RWANDA                        SECAM K1
SABAH/SARAWAK                PAL B
ST. KITTS                NTSC M                NTSC M
SAMOA                        NTSC M
SAUDI ARABIA                SECAM B/PAL B        SECAM G
SENEGAL                        SECAM K1
SEYCHELLES                PAL B                PAL G
SIERRA LEONE                PAL B                PAL G
SINGAPORE                PAL B                PAL G
SOMALIA                        PAL B                PAL G
SOUTH AFRICA                PAL I                PAL I
SPAIN                        PAL B                PAL G
SRI LANKA                PAL B
SUDAN                         PAL B                PAL G
SURINAM                        NTSC M                NTSC M
SWAZILAND                PAL B                PAL G
SWEDEN                        PAL B                PAL G
SWITZERLAND                PAL B                PAL G
SYRIA                        SECAM B
TAHITI                        SECAM K1
TAIWAN                        NTSC M                NTSC M
TANZANIA                 PAL B                PAL B
THAILAND                 PAL B                        
TOGO                        SECAM K
TRINIDAD Y TOBAGO        NTSC M                NTSC M
TUNISIA                        SECAM B
TURKEY                        PAL B                PAL G
UGANDA                        PAL B                PAL G
UNITED ARAB EMIRATES        PAL B                PAL G
UNITED KINGDOM                                PAL I                        
UPPER VOLTA                SECAM K1
URUGUAY                        PAL N                PAL N
USA                        NTSC M                NTSC M
VENEZUELA                NTSC M                NTSC M
VIETNAM                        PAL B                PAL G
YEMEN                        PAL B
YUGOSLAVIA                PAL B                PAL G
ZAIRE                        SECAM K1
ZAMBIA                        PAL B                PAL G
ZIMBABWE                PAL B                PAL G

  31.8) Cable channel allocation

(The following is from: (kruskal@watson.ibm.com (Vincent Kruskal)).

The following table gives the definitions of the numeric cable channels
defined in the EIA (Electronic Industries Association) Interim
Standards, IS-6 (CP), May 1983 and associated information that has been
gathered.  Definitions appear at the end.

Channel  Carrier Cable Band  Other Names
-------- ------- ----------- --------------------------

    1     72 MHz Low   (VAR) A-8, C54, J54, G64, 4+, 5A
    2     54     Low
    3     60     Low
    4     66     Low
    5     78     Low         A-7, C55, J55, G65
    6     84     Low         A-6, C56, J56, G66

    7    174     High
    8    180     High
    9    186     High
   10    192     High
   11    198     High
   12    204     High
   13    210     High

   14    120     Mid         A
   15    126     Mid   (ATC) B
   16    132     Mid   (ATC) C
   17    138     Mid   (VAR) D
   18    144     Mid   (VAR) E
   19    150     Mid   (VAR) F
   20    156     Mid   (VAR) G
   21    162     Mid   (VAR) H
   22    168     Mid   (VAR) I
   23    216     Super (VAR) J
   24    222     Super (VAR) K
   25    228     Super       L
   26    234     Super       M
   27    240     Super       N
   28    246     Super       O
   29    252     Super       P
   30    258     Super       Q
   31    264     Super       R
   32    270     Super       S
   33    276     Super       T
   34    282     Super       U
   35    288     Super       V
   36    294     Super       W
   37    300     Hyper       AA, W+1
   38    306     Hyper       BB, W+2
   39    312     Hyper       CC, W+3
   40    318     Hyper       DD, W+4
   41    324     Hyper       EE, W+5
   42    330     Hyper       FF, W+6
   43    336     Hyper       GG, W+7
   44    342     Hyper       HH, W+8
   45    348     Hyper       II, W+9
   46    354     Hyper       JJ, W+10
   47    360     Hyper       KK, W+11
   48    366     Hyper       LL, W+12
   49    372     Hyper       MM, W+13
   50    378     Hyper       NN, W+14
   51    384     Hyper       OO, W+15
   52    390     Hyper       PP, W+16
   53    396     Hyper       QQ, W+17
   54    402     Hyper       RR, W+18, C62
   55    408     Hyper       SS, W+19, C63
   56    414     Hyper       TT, W+20, C64
   57    420     Hyper (HAM) UU, W+21, C65
   58    426     Hyper (HAM) VV, W+22, C66
   59    432     Hyper (HAM) WW, W+23, C67
   60    438     Hyper (HAM) AAA, W+24, C68
   61    444     Hyper (HAM) BBB, W+25, C69
   62    450     Hyper (HAM) CCC, W+26, C70
   63    456     Hyper       DDD, W+27, C71
   64    462     Hyper       EEE, W+28
   65    468     Ultra       U14, FFF, W+29
   66    474     Ultra       U15, GGG, W+30
   67    480     Ultra       U16, HHH, W+31
   68    486     Ultra       U17, III, W+32
   69    492     Ultra       U18, JJJ, W+33
   70    498     Ultra       U19, KKK, W+34
   71    504     Ultra       U20, LLL, W+35
   72    510     Ultra       U21, MMM, W+36
   73    516     Ultra       U22, NNN, W+37
   74    522     Ultra       U23, OOO, W+38
   75    528     Ultra       U24, PPP, W+39
   76    534     Ultra       U25, QQQ, W+40
   77    540     Ultra       U26, RRR, W+41
   78    546     Ultra       U27, SSS, W+42
   79    552     Ultra       U28, TTT, W+43
   80    558     Ultra       U29, UUU, W+44
   81    564     Ultra       U30, VVV, W+45
   82    570     Ultra       U31, WWW, W+46
   83    576     Ultra       U32, AAAA, W+47
   84    582     Ultra       U33, BBBB, W+48
   85    588     Ultra       U34, CCCC, W+49
   86    594     Ultra       U35, DDDD, W+50
   87    600     Ultra       U36, EEEE, W+51
   88    606     Ultra (RA)  U37, FFFF, W+52
   89    612     Ultra       U38, GGGG, W+53
   90    618     Ultra       U39, HHHH, W+54
   91    624     Ultra       U40, IIII, W+55
   92    630     Ultra       U41, JJJJ, W+56
   93    636     Ultra       U42, KKKK, W+57
   94    642     Ultra       U43, LLLL, W+58
   95     90     Low   (FM)  A-5, C57, J57
   96     96     Low   (FM)  A-4, C58, J58
   97    102     Low   (FM)  A-3, C59, J59
   98    108     Low         A-2, C60, J60, G60
   99    114     Low         A-1, C61, J61, G61
  100    648     Ultra       U44, MMMM, W+59
  101    654     Ultra       U45, NNNN, W+60
  102    660     Ultra       U46, OOOO, W+61
  103    666     Ultra       U47, PPPP, W+62
  104    672     Ultra       U48, QQQQ, W+63
  105    678     Ultra       U49, RRRR, W+64
  106    684     Ultra       U50, SSSS, W+65
  107    690     Ultra       U51, TTTT, W+66
  108    696     Ultra       U52, UUUU, W+67
  109    702     Ultra       U53, VVVV, W+68
  110    708     Ultra       U54, WWWW, W+69
  111    714     Ultra       U55, AAAAA, W+70
  112    720     Ultra       U56, BBBBB, W+71
  113    726     Ultra       U57, CCCCC, W+72
  114    732     Ultra       U58, DDDDD, W+73
  115    738     Ultra       U59, EEEEE, W+74
  116    744     Ultra       U60, FFFFF, W+75
  117    750     Ultra       U61, GGGGG, W+76
  118    756     Ultra       U62, HHHHH, W+77
  119    762     Ultra       U63, IIIII, W+78
  120    768     Ultra       U64, JJJJJ, W+79
  121    774     Ultra       U65, KKKKK, W+80
  122    780     Ultra       U66, LLLLL, W+81
  123    786     Ultra       U67, MMMMM, W+82
  124    792     Ultra       U68, NNNNN, W+83
  125    798     Ultra       U69, OOOOO, W+84

  31.9) Notes on cable and broadcast frequencies

(The following is from: (kruskal@watson.ibm.com (Vincent Kruskal)).

RF band: To get the band, subtract 1.25 from picture carrier (low end)
and add 4.75 (high end).

Color subcarrier: Add 3.58... to picture carrier.

Sound carrier: Add 4.5 to picture carrier.

HRC: Harmonically Related Carrier.  Makes both second- and third-order
beats invisible by making them fall directly on the picture carrier of
other channels.  That is, multiplying the picture carrier by two or
three will yield exactly another picture carrier.

IRC: Incrementally Related Carrier, add 1.25 to HRC frequency.  A
General Instruments (Jerrold) catalog said that IRC makes third-order
(more important than second-order) beats invisible by making them fall
directly on the picture carrier of other channels.  But it is not true
that multiplying an IRC picture carrier by two or three yields another
IRC picture carrier.  This contradiction has not been resolved.  The
reason third-order harmonics are more important is that oscillators and
amplifiers tend to generate odd-order harmonics far more than even-order

Broadcast frequency: Add 1.25 to HRC frequency except for channels 5 and
6.  For them, subtract 0.75.  But these are just nominal frequencies.
The FCC actually has three channel designations for each number as in 5,
5- and 5+.  The minus channels are 10 kHz below the nominal value and
the plus channels are 10 kHz above.  For example:

  31.10) How did the (vertical) frame rate get chosen

Some people think that TVs are synchronized to the local power line since the
vertical scan rate is around 60 Hz (or 50 Hz).  This is not correct.

No TV (at least once the broadcast standards were defined - some experimental
schemes did) ever used the power line for synchronization.  However, older TVs
had line frequency power transformers (no SMPSs) whose stray magnetic fields
could affect the CRT deflection slightly.  So it made sense (well, this is one
justification at least) to make the vertical scan rate (field rate) equal to
the power line frequency.  Otherwise, there would be a jiggle or wiggle in the
picture due to the stray magnetic field affecting the deflection of the beam
inside the CRT.  Since it was thought at the time (and for other reasons as
well like cost) that 60 Hz was adequate to produce an acceptable amount of
flicker, this all fit together nicely.

In the good old days before color TV, the frame/field rate was exactly 30/60
Hz (or 25/50) Hz. With color, it had to be changed slightly (see the section:
"Why is the NTSC color subcarrier such a weird frequency?") but since TVs no
longer use line power transformers, there would not even be a slow position
shift (period of several seconds) due to this so it didn't matter.

  31.11) Why is the NTSC color subcarrier such a weird frequency?

(The following is from Bob Myers (myers@fc.hp.com)).

Actually, if we wanted to define the rates to the Nth degree, the important
starting point is the field rate.  The NTSC color frame rate was defined as
(60 * 1000/1001) Hz, which is a bit more than 59.94 Hz.  From this rate, all
the others in the system are defined.  The line rate is 262.5 times this, and
the color subcarrier is defined as 455/2 times the line rate.  This is often
given as simply 3.579545 MHz, but the the color subcarrier was actually
derived from the line/field rates rather than the other way around.

The whole thing was done so as to avoid (or at least minimize) interaction
between the luminance, chrominance, and audio subcomponents in the standard
color signal.  This could have been achieved by moving either the audio
subcarrier or adjusting the line and frame rates as described above.
Unfortunately, the latter route was chosen, leaving us with this very
strange looking set of rates.

The precise color burst frequency winds up being 3.579545.4545... under
this definition, but giving it to the nearest Hz is within the tolerances
of the system.

  31.12) What is the maximal allowed deviation of the horizontal frequency?

(The following is from: Peter Bennett VE7CEI (bennett@triumf.ca))

In Canada and the US (525 line, 60 HZ, NTSC), the horizontal frequency is
15,734.264 Hz.  The colour subcarrier is 455/2 times the horizontal
frequency which should come to 3.579545 MHz. I believe the tolerance on
the subcarrier frequency is +/- 10 Hz.

  31.13) Informal comparison of TV standards

Q: I heard that TV in certain part of Europe has more quality in
Europe then here in North America.  I'd like to know the differences between
the two systems.  Is that why we cant use video tapes from there?

(Responses from: Mark Zenier (mzenier@netcom.com or mzenier@eskimo.com))

The first difference is that a lot of the world runs on 50 Hz power
as opposed to North America's 60 Hz power.  In the olden days, before
active power supply regulators got cheap, it was decided that the
vertical scan rate match the power supply frequency, so that ripple
in the power supply wouldn't produce obnoxious visual effects.

So the PAL/SECAM signals have 50 vertical scans per second.

I don't know the exact reasoning, but the horizontal scan rate is
close to the same.   15750 (now 15734) for 60 Hz, and 15625 for 50 Hz
systems.  My guess is the tradeoff between cost (50 years or so ago) 
and audibility for a large portion of the population.

So 50 Hz systems have more lines - 625 vs. 525 lines for
60 Hz systems.

The second difference is that European TV channels are wider.  7 or 8 MHz
compared to the North American 6 MHz.  Video bandwidth is limited to 
4.2 MHz in a 6 MHz channel, but can be as much as 6 MHz in some of the
50 Hz systems.  (Note: Systems is plural.  There are many different
European systems with incompatible color and sound transmission methods.)

As for the quality, if you move a little farther away, so that a pixel 
on each system subtends the same angle, NTSC doesn't have a poorer 
picture, just a smaller one.

  31.14) PAL-plus

"I wonder if you could tell me about PAL-Plus.  The last time I
 was in Germany was in '84 so I've been out of touch with them."

(From: Jeroen H. Stessen (Jeroen.Stessen@ehv.ce.philips.com)).

Oh boy, here goes another long story:

PAL-plus is an attempt to extend the life-cycle of terrestrial PAL
transmissions by including compatible wide-screen (16:9) transmissions. It
is an advanced variant of the letterbox format, this means that when you
receive a PAL-plus widescreen program on an older 4:3 receiver you will see
black bars top and bottom.  It was originally developed in Germany (university
of Dortmund in cooperation with German terrestrial broadcasters and some
setmakers). Later a large consortium of European and Japanese setmakers took
over and finished the job. Strangely, the German broadcasters seem to use
PAL-plus only very rarely.

The PAL-plus standard comprises three extensions to the PAL-standard:

1. Vertical helper. In order to compensate for the fact that 1/4 of the video
   lines are not used, which would deteriorate vertical resolution for the
   widescreen viewer, the missing vertical information has been coded into
   the black lines in a manner as to be nearly invisible on a 4:3 receiver
   (you see some dark blue).  The 16:9 PAL-plus receiver combines 432 visible
   lines plus 144 helper lines into 576 new visible lines.

2. Colour-plus. The PAL colour carrier is modulated in a slightly different
   way (making use of correlation between 2 fields) in order to give a cleaner
   Y/C separation in the PAL-plus receiver.

3. Signaling bits from which the receiver can conclude whether the
   transmission is 4:3/16:9/PAL-plus and adapt the display format accordingly.
   The bandwidth of these bits is low enough to survive recording on a VHS

In order to enable a poor-man's PAL-plus receiver, the standard permits using
the mark "PAL-plus" if at least the vertical helper reconstruction is included.
Colour-plus is optional, so you will find sets on the market with only half of
the PAL-plus extension.

PAL-plus may also be combined with teletext, ghost cancellation reference,
digital Nicam stereo, VPS, PDC and what-you-have more.  Theoretically it can
be broadcast over a satellite channel too, but it was not designed for that
and some aspects of a satellite channel do indeed give interesting technical

There are also sets marketed as "PAL-plus compatible". These are mostly
widescreen sets without any PAL-plus processing at all, but they allow
switching of the display format between 4:3 and 16:9. They may well do that
automatically, based on the signaling bits. 

There are 2 methods for displaying a 4:3 letterboxed signal on a 16:9 display,
without using the PAL-plus helper lines:

1. Increase of the vertical deflection amplitude to display only the centre
   432 lines.

2. Vertical interpolation without using the helper, to convert 432 lines into
   576 lines and display on a 576 lines display.

Both modes may be called "movie expand".  Only when you really convert to
full-resolution widescreen will it be called "widescreen".

And there are 4 methods for displaying a regular 4:3 signal on a 16:9 display
(regular PAL, has nothing to do with PAL-plus):

1. Decrease of the horizontal deflection amplitude, this gives black bars left
   and right.

2. Horizontal interpolation, to convert N pixels to 3/4*N pixels.  Both modes
   may be called "4:3" or "normal".

3. Non-linear horizontal deflection waveform, called "Panorama mode" by JVC,
   works by increasing the S-capacitor value.

4. Non-linear horizontal interpolation, called "Superwide" by Philips, works
   with an advanced sample-rate converter.

With both modes, the left and right edges of the picture will be stretched to
fill the left and right bars, but the aspect ratio of the centre part of the
picture will hardly be affected.

Interesting, huh?

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