DE1006461B - Method for monitoring the linearity of television transmission systems, in particular television transmitters - Google Patents

Description

GERMAN

The invention relates to a method for monitoring the linearity of television transmission systems, especially high-frequency transmitters and relay lines.

In order to avoid gradation distortions in the television picture, certain requirements must be met by the Linearity of the modulation characteristic can be set. The distortion factors of simple tube amplifiers can be achieved determine by means of appropriate measuring bridges. But in a television broadcast system there are the most varied Types of amplifiers (e.g. keyed amplifiers, amplifiers with clamping diodes, etc.) which in many cases a standard-compliant image, blanking and synchronization signal (BAS signal) Need to check that they are working properly. A distortion factor measuring bridge fails here.

If a Röbrenk curve is controlled with an ideal saw tooth, a corresponding result results the tube characteristic distorted sawtooth. The linearity of the characteristic can therefore be measured.

When measuring with the aid of an oscilloscope, this procedure assumes that the oscilloscope even works 100% linearly. Distortion up to In practice, however, 10% can no longer be measured with this known method. For this There are other inaccuracies caused by the curvature of the oscilloscope tube. A Such a method therefore does not meet greater accuracy requirements.

It is now known to use a stair step instead of the sawtooth for control. this means that the sawtooth is divided into certain sections and these in the form of defined Jumps can be evaluated as a measure for the image transmission. But also with this procedure is the accuracy of the measurement is not significantly increased, and as a result, non-linearity of the oscilloscope can this also results in incorrect measurements.

According to another known method, a sinusoidal voltage is used as the measuring voltage, which is superimposed on an HF, e.g. 250 kHz over 250Hz, with the HF after passing through the test object is again separated from the 250-fIz components and is further used for display. This Although the method provides good measurement accuracy, the correct operation of the entire transmission system cannot be determined if black-controlled amplifier trains are available. Furthermore, the low-frequency ones are missing after the separation Voltage sinusoidal amplitude the defined assignment of the amplitude range to the Image content, unless special display methods are used due to additional effort. Furthermore, the measurement signal is in this known method

for monitoring the linearity

of television broadcasting systems,

especially television channels

Applicant:

C. Lorenz Aktiengesellschaft,

Stuttgart-Zuffenhausen,

Hellmuth-Hirth-Str. 42

Kurt Wolf, Wildbad (Black and White),
has been named as the inventor

Method no BAS signal, d. That is, the ones necessary for the transmission of a television signal are missing technical information in the form of impulses, black shoulders, etc., and the implementation of z. B. a keyed black control is therefore not possible; thus just the possibilities are missing Measurement under normal operating conditions in television transmission systems.

The invention overcomes these disadvantages. It is characterized in that a complete picture, blanking and synchronizing signal (BAS signal) is used, the picture content of which consists of a linear, sawtooth-shaped and line-frequency voltage on which a high-frequency, sinusoidal voltage is superimposed. After passing through the transmission system, the image, blanking and synchronizing signal is passed over a high-pass filter whose cut-off frequency fg in the lower range corresponds to the frequency of the superimposed HF. As a result, all pulse components are filtered out, and only the HF sinusoidal voltage remains, which is fed to an oscilloscope for the measurement evaluation of the linearity of the transmission system, so that, as a result of the use of the linear, sawtooth-shaped voltage, an assignment can also be made after this (mentioned) displacement of the high-frequency sinusoidal voltage the amplitudes of the image content from black to white are available.

The assignment of the values mentioned is therefore carried out with sufficient accuracy without a special one Effort is required. The superimposed HF is preferably in the range between 1 and 5 MHz. With

«09 869/146

the associated synchronization signal thus creates a complete BAS signal. The BAS signal for the linearity measurement works with a line-frequency sawtooth voltage as the image content, whereby the sawtooth begins at the end of the rear black staircase and, with increasing gray value, merges with the white tip up to the beginning of the next front one Black stairs run linearly.

Aside from that. ..Advantage that after the. Screening one Assignment of the amplitude range to the image content from black to white is the result further advantage of that. Incorrect measurements due to non-linearity of the display device are avoided. In the end a complete BAS signal with the for ■ technical information typical for the transmission of a television signal can be used. Through this is a test of all transmission elements, such as television transmitters, relay lines, studio amplifiers, etc., possible, regardless of whether these links are black-controlled or not. After all, this drive still the advantage that z. B. when using a video measuring frame only by actuation a mode switch, the most varied of measurement signals can be changed as image content, at which the linearity measurement represents only a single term. When using a corresponding sinusoidal voltage would have to take place in each case an entire switchover of the transmission path, since z. B. the Black control would have to be switched over in all black-controlled amplifier trains.

The invention is explained in more detail with reference to the drawing, which shows an exemplary embodiment.

Figs. 1 and 2 schematically show the relationships in a known method of using a Sinusoidal voltage with superimposed HF;

Fig. 3 shows a schematic block diagram of an arrangement for carrying out the invention \ ^r erf ahrens;

4 shows oscillograms for a more detailed explanation of the invention (the deflection A is shown as a function of the time t ).

According to known methods, the sinusoidal oscillations 1 of the frequency f _x of z. B. 250 Hz an HF oscillation 2 of z. B. 250 kHz superimposed. After passing through the test piece, the shape of the high-frequency voltage (in Fig. 1, and after separation of the HF from the LF by the high-pass filter 3 (cut-off frequency f _g> ^ ₁₎ shown in Fig. 2 results in Fig. 2 as envelope 4 shown).

As can be seen, the curves in FIG. 2 lack the sync pulses and the black level indicators and white. It is therefore not possible to specify where z. B. black or white exactly starts or stops.

In an arrangement for performing the method according to the invention, for. B. on the encoder side the measuring frame 5 is provided (Fig. 3), in which the sawtooth the HF is superimposed (see. Oscillogram 4 °, recorded at point α in Fig. 3) and represents the image content.

7 is a high-pass filter for filtering out the high frequency. ^{The oscillogram 4 &} recorded with the aid of the oscilloscope 8 at point b (FIG. 3) shows the envelope curve in short-circuit operation. The signal from the measuring frame 5 via the test object 10 (oscillogram 4. ^c , recorded in front of the HF sieve 11) and the HF sieve 11 is then sent via the connection 9. An image corresponding to the oscillogram 4 ^d (behind the HF sieve) is now visible on the screen of the oscilloscope. The envelope curves show an exact assignment of the amplitudes to the image content from black to white, and the linearity can be read with any desired accuracy.

The lines 12 and 13 indicate the position of the synchronous signal (Fig. 4 a, 4c) and that by differentiation of the edges of these synchronizing pulses (Fig. 4b, 4d). By the lines 13., 14 the position of the back porch is indicated, while 15.16 indicates that of the anterior porch is designated. Lines 14, 15 enclose the image content, with 14 denoting black and 15 is assigned the value white. The HF (Fig. 4d) is a measure of the gain in the relevant Amplitude range (steepness). Therefore, through this measurement there is a continuous sampling of the Slopes of the entire transfer characteristic take place, and the slope of the characteristic is thus simulated.

Claims (2)

Patent claims: 1. Method for monitoring the linearity of television transmission systems, in particular High-frequency transmitters and relay lines, characterized in that a complete picture, blanking and synchronizing signal (BAS signal) is used, the image content of which consists of a linear, There is a sawtooth and line frequency voltage, which is a high frequency, sinusoidal voltage Voltage is superimposed, furthermore that the image, blanking and synchronizing signal after passing through the transmission system is passed over a high pass whose cutoff frequency is in the lower Range corresponds to the frequency of the superimposed HF, and that the HF sinusoidal voltage according to Passing through the high pass for the technical evaluation of the linearity of the transmission system is fed to an oscilloscope. 2. The method according to claim 1, characterized in that the superposition frequency is approximately 1 to 5 MHz. 1 sheet of drawings © 609 869/146 4.57