DE1131263B - Circuit arrangement for the amplitude modulation of a carrier wave with a video signal - Google Patents

Description

The invention relates to a circuit arrangement for the amplitude modulation of a high frequency Carrier wave with a video signal provided with blanking gaps and television sync signals, directional guides switched in opposite directions are used.

A number of diode modulators are known which, among other things, differ with regard to the type the circuit, with regard to the complexity of circuit elements and with regard to the useful signal frequency band differentiate. Some of these modulators have the disadvantage that their input resistance changes greatly, so that the generator of the carrier frequency is loaded unequally. Other modulators either require a large amount of circuit elements or correspond with regard to the linearity does not meet the requirements set here. Some of the modulators use transformers, so that difficulties arise in the case of useful signals with a large frequency bandwidth. In particular a modulation circuit is known in which a carrier frequency and a useful signal two directional ladders switched in opposite directions are supplied. There are resistors in series with the directional ladders switched, which are dimensioned such that the entire modulation circuit is a largely linear Has characteristic. In addition, there is one output terminal for each of the generators for the Carrier frequency and grounded for the useful signal. This known modulation circuit is evident intended for a telephone transmission system, in particular carrier waves in the order of magnitude of 100 kHz can be modulated with useful signals of around 4 kHz. The carrier wave and the useful signal become a node of the modulation circuit via one and the same channel supplied L, and a constant input resistance of this modulation circuit does not appear to be essential to be. The aim of the invention is to provide a circuit arrangement which is suitable for the The much higher frequencies used in the television area are suitable.

According to the invention, the video signal and the carrier source are via mutually parallel Channels fed to the input of the circuit arrangement with a constant input resistance. This Input is with one electrode each of a first directional conductor and one connected in opposite directions second directional conductor conductively connected. Those facing away from the input of the circuit arrangement Electrodes of the first directional conductor or of the second directional conductor are connected via a working resistor or Circuit arrangement

for the amplitude modulation of a carrier wave with a video signal

Applicant:

Television. GmbH.,
Darmstadt, Am Alten Balmhof 6

Alfred Schneider, Darmstadt,
has been named as the inventor

directly connected to the ground potential. Depending on the polarity of the video signal, that is fed with negative or positive polarity is the first directional conductor in the reverse direction or in the reverse direction. polarized in the forward direction, and the amplitude-modulated signal is in a manner known per se decreased at the working resistance.

The carrier wave and the video signal are thus transmitted to the circuit arrangement according to the invention Channels lying parallel to one another are fed with constant input resistance. This results in the advantage that a relatively large high-frequency carrier wave can be fed directly to the modulator can without frequency modulation occurring. The circuit arrangement according to the invention is characterized is also characterized by high sensitivity, good linearity and extensive frequency independence the end.

The high-frequency carrier wave is expediently fed through a capacitor, which is dimensioned such that it has a relatively large resistance on the one hand for the video signal and on the other hand represents a relatively low resistance for the carrier frequency.

Embodiments of the invention are explained in more detail with reference to FIGS. 1 and 2, the same Components are designated with the same numbers. Only those necessary for understanding are shown in the figures Components drawn. It shows

1 shows the basic circuit diagram to explain the mode of operation of the modulator according to the invention,

Fig. 2 shows a high frequency generator and modulator.

209 609/182

According to Fig. 1, the video signal is supplied via terminal 1 and resistor 2 (1 kΩ) and the high-frequency carrier wave is supplied via terminal 3 and capacitor 4 (5pF). The capacitor 4 should be dimensioned such that it represents a low resistance for the high-frequency carrier wave and a relatively high resistance for the video signal. The diodes 5 and 6 are polarized in opposite directions, in such a way that when the video signal is fed in, the diode 5 is switched in the forward direction and the diode 6 in the reverse direction. A working resistor 7 (100 Ω) ensures that - in conjunction with all other circuit elements - the resistance at the output is approximately equal to the characteristic resistance of the cable 8 via which the modulated signal is to be fed to a receiver (not shown). The choke 9 is dimensioned such that it represents a low resistance for the video frequency voltages. If a negative voltage occurs at the circuit point α , the resistance of the diode 5 increases, whereas that of the diode 6 decreases. As a result, the input resistance of the modulator at circuit point α remains practically constant. This measure increases the sensitivity of the modulator and improves its linearity. The constant input resistance of the modulator has the particular advantage that a relatively large high-frequency carrier wave can be fed directly to the modulator without frequency modulation occurring.

The circuit arrangement according to FIG. 2 essentially consists of the input stage A, the black control B, the emitter stage C, the high-frequency generator D and the modulator E.

Via terminal 11 and the electrolytic capacitor 12 (100 μΡ) a with blanking gaps and synchronous signals provided video signal fed to the base of transistor 13 with positive polarity. In this transistor stage, to which the resistors 14 (30 kΩ), 15 (10 kΩ),. 16 (300 Ω), 17 (1 kQ) and the capacitor 18 (100 pF) belong, this video signal is amplified and appears with negative polarity at the collector of transistor 13.

Via the electrolytic capacitor 19 (10 μ ¥) the signal is then fed to the base of the transistor 21, with the diode 22 (type OA 5) and the resistors 23 (1 kΩ), 24 (10 kΩ.) (As a voltage divider) one Black control is made. The transistor 21 (type OC 6015) and the resistors 25 (1 kΩ), 26 (500 Ω) are connected as emitter follower stage C, so that the signal is transmitted to the following modulator E with low resistance via the resistor 27 (1 kΩ).

The high-frequency generator D consists of the transistor 28 (type OC 6015), the resistors 29 (4OkQ) ₁ 31 (1OkQ) ₅ 32 (10 Ω), 33 (400 Ω), further from the capacitors 30 (2.2 nF), 34 (4.7 nF), 35 (500 pF), 36 (5OpF), 37 (10 to 40 pF), 38 (10 nF), the electrolytic capacitor 39 (100 μ ¥) and the resonant circuit coil 41. The capacitor 37 is tuned in such a way that a high-frequency carrier frequency of about 55 MHz is generated corresponding to channel 3 and is fed via the coupling capacitor 42 (5 pF) to the modulator E , the function of which has already been described with reference to FIG. The amplitude-modulated signal is then fed via the cable 8 either to a commercially available home television receiver (not shown) or, for the purpose of broadcasting via a power stage, to an antenna (not shown).

Claims (5)

PATENT CLAIMS: 1. Circuit arrangement for the amplitude modulation of a high-frequency carrier wave with a video signal provided with blanking gaps and television sync signals using directional conductors connected in opposite directions, characterized in that the video signal and the carrier wave are fed to the input (α) of a modulator with constant input resistance via channels lying parallel to one another, that the input (a) is conductively connected with one electrode of a first directional conductor (5) and a second directional conductor thereto connected in opposition (6) that this node (d) remote from the electrodes of the first directional guide (5) and the second directional guide (6) are conductively connected via a load resistor (7) or directly to the ground potential, so that the first directional conductor (S) is polarized in the reverse or forward direction, depending on whether the video signal is supplied with negative or positive polarity, and that the amplitude-modulated signal in on is removed in a known manner on the work resistor (7). 2. Circuit arrangement according to claim 1, characterized in that the high-frequency Carrier wave is fed through a capacitor (4), which is dimensioned such that it on the one hand a relatively large resistance for the video signal and on the other hand for the carrier frequency represents a relatively low resistance. 3. Circuit arrangement according to claim 1, characterized in that parallel to the working resistance (7) a throttle (9) is connected, which is dimensioned such that it is for the video frequency signal represents a relatively low resistance. 4. Circuit arrangement according to claim 1, characterized in that the modulated signal is passed on via a cable (8) and that the working resistance (T) is dimensioned such that its amount is equal to the characteristic resistance of the cable (8). 5. Circuit arrangement according to claim 1, characterized in that the video signal with negative polarity is fed to the base of a transistor (21) connected as an emitter follower stage (Q ) and that the base of this transistor (21) with the anode of a directional conductor (22) and the cathode this directional conductor (22) is conductively connected to a circuit point, the potential of which is adjustable in such a way that a black control preferably responding to the pulse base of the sync pulses is achieved. Considered publications:
French Patent No. 1,051,995;
U.S. Patent No. 2,116,559. 1 sheet of drawings © 209 609/152 6.62