JPS5946467B2 - Ghost signal removal device - Google Patents

Description

[Detailed description of the invention] The present invention relates to a ghost signal removal device.

As shown in FIG. 1, the conventional ghost signal removing device is composed of an input terminal 1, an output terminal 2, a distributor 3, a combiner 4, and a cancellation signal generation circuit 5. The cancellation signal generation circuit 5 has a step-variable level. Adjustment circuit, '6, Continuously variable level adjustment circuit T) Consists of a delay time coarse adjustment circuit 8, a step delay time adjustment circuit 9, and a continuously variable phase shift circuit 10.

As shown in FIG. 2, the input terminal 1 receives a main signal s and a signal A accompanied by a ghost symbol G1, which is divided into two by a distributor 3.
One is straight and goes to the combiner 4, and the other is adjusted like signal B in the cancellation signal generation circuit 5 and goes to the combiner 4. That is, the signal A is adjusted in the cancellation signal generation circuit 5 so that the level and position of the main signal S are the same as those of the ghost signal G, and the polarity is reversed (signal B
) By adding the signal A and the signal B in the synthesis stage 4, a signal C from which the ghost signal has been removed is outputted from the output terminal 2.

In this case, a small level ghost signal G1 is generated in the signal C, but there is no problem in practical use. In the ghost signal removing apparatus described above, there are many points that need to be adjusted, which requires time and skill.

The main reason for this is that the ghost signal cannot be removed unless the signal level and delay time are adjusted extremely accurately in the cancellation signal generating circuit 5. In particular, delay time adjustment is extremely important; for example, if the delay time adjustment is incorrect by π radians in terms of phase shift (although it is only a small amount in terms of delay time), the ghost signal will be strengthened. It will end up being put away. Therefore, when adjusting the delay time, place a waveform monitoring oscilloscope on the output terminal 2 and switch between the delay time rough adjustment circuit 8 and the step type delay time adjustment circuit 9 while monitoring the output ghost signal.
Each time, it is necessary to adjust one continuously variable phase shift circuit and search for the point where the level of the ghost signal on the oscilloscope is minimized, which is extremely time-consuming and troublesome.

The present invention has been made in view of the above, and an object of the present invention is to provide a ghost signal removal device that eliminates the difficulty of adjustment when removing ghost signals and is easy to adjust.

The key point of the present invention is that the cancellation signal generation circuit includes a manually variable phase shift circuit that changes the phase shift angle using a manual dial type, and an automatic variable phase shift circuit that automatically changes the phase shift angle at a certain period. This point will be explained with reference to FIGS. 3 and 4.

FIG. 3 is a block diagram of the ghost signal removing device according to the present invention, and the same parts as in FIG. 1 are given the same numbers.

The cancellation signal generating circuit 35K has an automatic variable phase shift circuit 11 and a manual variable phase shift circuit 12 incorporated in parallel. When removing the ghost signal, first, the automatically variable phase shift circuit 11 is used, and while the phase shift angle is periodically changed as shown in FIG. 8 and 9 to adjust the level and delay time of the ghost signal. If the level and delay time adjustments are significantly different from the conditions for canceling the ghost signal, the level of the ghost signal at output terminal 2 will be
1, and the minimum value of the level of the ghost signal is quite large. As the conditions for canceling the ghost signal are gradually approached, the level of the ghost signal changes as shown in G2, and the level of the ghost signal decreases.Finally, when the conditions for canceling the ghost signal are met, the level of the ghost signal changes as shown in G. The minimum value of the level approaches almost zero. At this time, manually variable phase shift circuit 1
Switch to 2, output terminal 2! By making fine adjustments so that the level of the ghost signal at C is minimized, the ghost signal can be successfully removed. An embodiment of the present invention is applied to the IF band (16.5 to 22
65MHZ) will be described as an example.

FIG. 5 shows the configuration of the cancellation signal generating circuit 35 which is the main part of the present invention.

The cancellation signal generation circuit 35 includes a step variable level adjustment circuit 6, a continuously variable level adjustment circuit 7, and a delay time coarse adjustment circuit 8.
, a step type delay time adjustment circuit 9, and a variable phase shift circuit 13 including a manual variable phase shift circuit and an automatic variable phase shift circuit. The step-type delay time adjustment circuit 9 is made up of a cascade connection of five types of delay circuits having delay times of, for example, 10, 20, 40, 80, and 160 ns, and the on/off combinations of these delay circuits provide a delay time of 10 ns from 0 to 310 ns.
It is variable in steps.

The minimum step is 10 ns, which is approximately 80 degrees when converted to an IF band carrier wave phase shift, so the variable phase shift circuit 13
Theoretically, a phase shift angle of 180 degrees is sufficient for use. The variable phase shift circuit 13 is a so-called Yauman circuit driven by a low impedance amplifier LA and terminated by a high impedance amplifier HA, where θ=2tan-12πFCR (
f: frequency, it is possible to obtain a variable phase shift range of 0<C00). In this variable phase shift circuit 13, Cl,
C, are manual and automatic variable capacitors, respectively.
By making this variable, the phase shift angle can be changed. It is assumed that the manual variable capacitor C1 and the automatic variable capacitor C are switched by a switch S, and C2 is used only during ghost signal removal adjustment, and C1 is used after adjustment.

As the manual variable capacitor C1, a so-called air variable condenser, polyvariable condenser, or the like is used.

The sixth method for realizing the automatic variable capacitor C2 is
As shown in the figure, there are variable means by voltage control using a variable cap VC, etc., and variable means by mechanically driving a variable capacitor once by a motor MVC as shown in FIG.

Ghost signals are removed using the above-described specific configuration, but since its operation has been described above, it will not be repeated here.

Although a feedback type ghost removal device has been described so far, it is clear from the operating principle described above that the present invention can be applied to any configuration of ghost removal device such as a feedback type ghost removal device.

As described above, according to the present invention, the adjustment procedure for removing ghost signals, which has been considered extremely troublesome in the past, can be simplified.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a conventional example, Fig. 2 is an explanatory diagram of the principle of removing ghost signals, Figs. 3 and 4 are explanatory diagrams of the operating principle of the present invention, and Fig. 5 is an explanatory diagram of an embodiment of the present invention. The example illustrations, FIGS. 6 and 7, are illustrations of automatically variable phase shifting circuits used in the present invention. 3: Distributor, 4: Combiner, 5, 35: Cancellation signal generation circuit, 6, 7: Signal level adjustment circuit, 8, 9: Delay time adjustment circuit, 11: Automatic variable phase shift circuit, 12: Manual variable 13: Variable phase shift circuit.

Claims (1)

[Claims] 1. A distributor that branches a signal accompanied by a ghost signal, a cancellation signal generation circuit that forms one of the split signals into a cancellation signal for canceling the ghost signal, and In a ghost signal removal device constituted by a synthesizer for synthesizing the other signal, the cancellation signal generation circuit includes a signal level adjustment circuit, a delay time adjustment circuit, and a variable phase shift circuit, and the variable phase shift circuit comprises: A ghost characterized in that an automatic variable phase shift circuit that automatically changes the phase shift angle at a certain period and a manual variable phase shift circuit that manually changes the phase shift angle are incorporated in parallel. Signal removal device.