SECAM

SECAM one is particularly in and Eastern Europe common similar Television standard for those Ink transfer and became of Henri de France developed and 1956 presented. The abbreviation SECAM stands for Séquentiel couleur avec Mémoire, too German "Sequenzielle color with memory".

Philosophy

Exactly the same as NTSC and it concerns a system for black-and-white television compatible ink transfer. While PAL represents an improvement of the ink transfer system of NTSC, with SECAM completely different method of the conversion of this task was found.

Thing in common with NTSC and PAL

As is the case for NTSC and PAL in form of two color difference signals -- "red minus brightness" and "blue minus brightness" -- will transfer additionally the color information necessary for the brightness (thus the black-and-white picture) and then by means of frequency combing into the upper frequency range of the BAS signal trained.

For the bases that Ink transfer see ebenda. See also: Television signal.

Function mode

SECAM uses those for the ink transfer instead of with NTSC and PAL the occurring . The advantage of the frequency modulation is in the fact that phase shifts cannot change the information signal, thus the color information. But there is no possibility of accommodating two signals in a carrier frequency thus no counterpart to Quadrature amplitude modulation. This meant, it can per line in each case Color difference signal are transferred. Therefore both colors are transferred picture-line by line alternating; the color transferred in each case is stored and used for the representation of the next line again. For the two color information two different carrier frequencies are used, between which accordingly line by line one switches.

With PAL into the demodulation frequently two character rows combined and thus likewise the color information of two lines summarized, which vertical color dissolution halves thus, however will become with PAL the color information with full vertical dissolution to transfer in principle.

The dissolution reduction does not have an effect, since human eyes possess a far smaller sensitivity for color information than for brightness information and therefore both the horizontal and the vertical color dissolution are reduced.

Delay lines

For SECAM one must have Delay lines in the receiver, in order to store the color signal for the duration of a line, while one can do with PAL without it (simple PAL). However such lines are available since beginning of the 60's low-priced.

Narrow band FM

The crucial disadvantage of SECAM is its susceptibility to interference, whereby noise leads to "color fires". Therefore the abbreviation SECAM is interpreted frequently jokeful with "Seven extra Colours A minute" (sieved additional colors per minute). In contrast to the UKW broadcast it acts not around a bind-spreading procedure! Thus 15 kHz frequency range of a radio ending with 75 kHz are modulated, the factor 5 decreased here disturbance sensitivity immensely. For such a factor is in the frequency allocation of the television stations no place. Consequently the signal is very disturbance sensitive, which particularly carry with the satellite-to-receiver telecasting to comes - here one should generally do without SECAM.

Compatibility with black-and-white pictures

The color subcarrier is due to the used frequency modulation independently of the chroma always equal intensively in the picture present. The carrier is switched therefore regularly in the phase, in order to avoid spurious patterns, what does not succeed however perfectly. With genuine black-and-white transmissions it was therefore completely switched off on the GDR television.

Over screens

SECAM modulated signals leave themselves not over-dazzles, for this reason uses one in the studio PAL and converts the signal only when radiating. So one could change over also the GDR television problem-free to PAL.

further disadvantages

The two color components do not have defined zero point. The viewer may do these instead by means of two color pass correction automatic controllers themselves to specify. Also the CROSS Color disturbances are most unpleasant with SECAM. They become apparent as blue and red strips, which out-flash at sharp edges, and/or. as intensively red color surfaces with fine samples.

Spreading

The development of SECAM in France was politically motivated, in order to be able to protect the native equipment industry against imported goods. In this connection the abbreviation becomes jokeful as "Système élégant contre l'Amérique", (dt. "elegant system against America") interpreted. During the introduction of SECAM in the former Eastern Bloc countries likewise political reasons played a role. France was in an approximation to these states. Further it wanted to reach a spreading of its system and studio and transmission technology favorably delivered. In the GDR one wanted to arrange west television unattractive, by being able to see it only to black-and-white. This was certainly only from short duration, since very soon PAL decoders in self-'s building developed and were equipped those at all few color television sets at least partially ex factory with SECAM/PAL decoders, after pure SECAM devices proved as unsalable.

Some the Eastern European countries their TV systems changed others over from SECAM to PAL, still are in the conversion.

One must note that SECAM France and SECAM Eastern Europe are not completely compatible: Many SECAM able televisions and video recorder (except French models) get along only with SECAM Eastern Europe, do not function however not with SECAM France.

MESECAM

MESECAM ("Middle East SECAM") is a procedure for the recording of SECAM signals on modified PAL-Video home systemVideo recorders. All MESECAM able devices control therefore always also PAL. MESECAM is in the Eastern European and non-European SECAM countries the usual recording technique. Also most in Germany as SECAM able sold Video home system Rekorder control actually only MESECAM. French video home system photographs use another recording technique for the color signal, which is not compatible with MESECAM. MESECAM devices - just like PAL devices - play therefore French SECAM photographs only black-and-white. The ability for colored playing of photographs from France is usually called in the trade "SECAM west".

SECAM IV - Linear NIR (NIIR) NIR Farbfernsehsystem

SECAM IV is a color television standard developed from Russian Forschungsinstitut NIIT. Actually two standards were developed: The nonlinear NIR, with which the square root of the color signal will transfer (in a procedure similar to gamma the correction), and the linear NIR, with which this process is omitted. SECAM IV as below described the linear version is called of NIR. Color test transmissions in NIR began 1963 in Moscow in UHF standard D, before a change on SECAM III at the same time with the start in France at the 1. October 1967 took place. The piece of news over the new Soviet color system reached the west 1966. At this time the BBC was quoted: "it is to be noticed from interest to that this suggestion identically to one in April 1963 by BBC engineer Mr. W. B. Pethers made appears, which was however not pursued, because its advantages were not attractive at that time regarding the other systems enough." The original system of Pethers was similar to that nonlinear NIR, and it developed likewise two variants. Test with NIR accomplished by the ITA in Great Britain with a strong lobby for its introduction to Europe, before the nations in the PAL SECAM division polarized themselves. Although derived from NTSC, SECAM IV differs both from the PAL- as well as from the SECAM system: It uses a "third way" for the avoidance of colour errors. In a line a PAL similar quadrature-amplitude-modulated signal with suppressed carrier will transmit and in the following line a same signal, however with constant phase position as reference. Both the line with color contents as well as the following line with the reference carrier the same transmission paths go through and therefore are demodulated signal freely from phase errors. A similar idea is used with the video recorder systems. The higher-frequency Chrominanzsignal is converted in a down-more frequent range and taken up together with a reference signal. During the rendition this reference is used as BFO for the recovery of the Chrominanzsignale. Since both signals go through the same tape operation impairments, the Chrominanzsignal appears jitter-free. SECAM IV/Linear NIR has two lack, which the other systems (NTSC, PAL and SECAM III) not to exhibit, and which develop from the use of the transferred reference signal in its wide-band form contrary to the usual locally produced reference carriers: First of all, because both the chrominance signal and the reference signal of the adjacent line are put on a ring demodulator, each spurious signal, which is present on both entrances, is demodulated and forms thereby a DC voltage portion of the exit. Dependent on the frequency of the spurious signal this results in either a total colouring or a colored sample. Secondly a reduced amplitude is present after demodulating the chrominance signal as effect of the Chromarauschens, which leads which to a Entsaettigung of the colors with face colors becomes particularly recognizable. As color carrier frequency one uses as with the PAL standard 4.433.618,75Hz with 625/50 SECAM IV. The color signals are developed transmitter-laterally as follows: R-Y with 1,14 and B-Y with 2,03 as derating factor. These baseband color difference signals have a range of > 1,5MHz. Afterwards the color difference signals on a carrier are modulated. Additionally a gleichspannungskomponente with 10% of the maximum value is added. As usual is the case for SECAM, the color identification switch in the receiver is synchronized through in the vertical synchronous blanking gap 40µs present long color carriers. The chrominance signal is again won by multiplication of the line B with (in one like also with PAL usual glass delay line) preceding the stored line A. The signal of the line B serves as reference oscillator for the line A signal, which contains the Chrominanzinhalte. Therefore its own color carrier reference oscillator is not necessary in the receiver. By the caused gleichspannungskomponente always a reference frequency is present. This should possess 10 to 20 subject larger an amplitude than the line signal A at the modulator entrance, which can be demodulated.

Note: The system would have to be offered after as also SECAM III a reduced Chroma dissolution of vertical to the description, since always 2 lines each can show only one line with the correct color kind. To what extent the Mitsenden of a color subcarrier within the visible video range of each second line to incompatibility problems with the S/W system leads can be only assumed. Advantage: No color oscillator in the receiver necessarily.