JPS62281Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Detailed Description of the Invention] The present invention relates to a tuning adjustment device for an electronically tuned tuner using a voltage variable capacitance element such as a variable cap.

In the tuning circuit of an electronically tuned tuner, a variable cap is generally used instead of a variable capacitor, as the capacitance changes depending on the applied DC voltage, thereby changing the tuning point frequency of the tuner. Adjustment of this electronically tuned tuner involves using tuning coils connected to each of the high frequency amplifier, frequency mixer, and local oscillator so that the tuner will tune to a predetermined frequency when a predetermined tuning voltage is applied to the varicap. It is necessary to adjust the inductance value. Normally, tuning of the tuner is performed at several points among the reception frequencies. For example, in the AM band, tuning is adjusted at three points: 540 KHz, 1100 KHz, and 1650 KHz. In this case, the voltage applied to the varicap must be switched and adjusted separately for each of the three points, and the adjustment at each point affects the tuning state of the other two points, so readjustment is necessary. It was inconvenient.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a tuning adjustment device that facilitates the adjustment of an electronically tuned tuner, and a tuning adjustment device that can adjust each point while checking the influence on other points. It is to be.

In order to achieve the above object, in the present invention, for a sweep oscillator that provides an oscillation output over the reception frequency band of the tuner to the antenna input of the tuner under test, the tuning voltage applied to the voltage variable capacitance element of the tuning circuit every sweep is applied to the antenna input of the tuner under test. is switched to a plurality of values, thereby displaying different tuning frequency characteristics of a plurality of tuning points.

The present invention will be explained below with reference to the drawings.

Figure 1 shows an electronically tuned tuner 1 according to the present invention.
6 shows a tuning adjustment device. This adjustment device includes a sweep oscillator 10 that oscillates a frequency output in the receiving frequency band of the tuner 16, a tuning voltage generator 14, a switching circuit 12 that switches the tuning voltage to the tuner 16, a detector 18 that receives the IF output of the tuner 16, and an oscilloscope 20.

The sweep signal generator 10 mainly includes a rectangular wave generator (not shown) that generates the rectangular wave shown in FIG. 2A, and an integrator (not shown) that integrates this rectangular wave to generate the sawtooth wave shown in FIG. (not shown) and a voltage controlled oscillator (not shown) which receives the sawtooth wave and generates a sweep signal whose frequency changes continuously. The sweep signal generator 10 supplies the rectangular wave shown in FIG. 2A to the switching circuit 12, the sawtooth wave shown in FIG. 2B to the horizontal input terminal H of the oscilloscope 20, and
A sweep signal of the receiving frequency of the tuner is applied to the antenna input of No.6.

The switching circuit 12 that receives the rectangular wave consists of a decimal counter, and when it receives the first pulse, it generates an output at the count "1" terminal and switches the analog switch 3.
4 is turned on, and when the next pulse is received, an output is generated to the count "2" terminal and the analog switch 3 is turned on.
Only the analog switch 36 is turned on, and when the next pulse is received, an output is generated at the count "3" terminal and only the analog switch 36 is turned on. When the fourth pulse is received, the decimal counter 12 is reset to generate an output at the count "1" terminal, so
Turn on the analog switch 32. In this way, the counter 12 is connected to the analog switches 32, 3
4 and 36 are turned on in order.

The tuning voltage generator 14 consists of a constant voltage source of 40 volts, and its output terminal is connected to the front end of the tuner 16 under test via variable resistors 22, 24 and 26 and analog switches 32, 34 and 36. It is connected to a varicap (not shown) connected in parallel to the coils of the tuned circuit connected to each of the high frequency amplifier, frequency mixer and local oscillator. The variable resistors 22, 24 and 26 have voltage drops of 10 volts, 20 volts and 20 volts on the output side.
Generates 30 volts of different tuning voltages.

The sweep signal received by the antenna input of the tuner 16 under test changes continuously from 540 KHz to 1650 KHz. For this AM frequency, the tuner 16
The varicap shall be adjusted so that the applied voltage can be tuned in the range of 10 volts to 30 volts. The IF output of the tuner 16 is applied to a detector 18 for positive detection, and the resulting tuning frequency characteristic is displayed on an oscilloscope 20.

The operation of this adjustment device will be explained with reference to FIG. The switching circuit 12 sends the pulse shown in FIG.
The pulse shown in FIG. 2D is applied to the analog switch 36, and the pulse shown in FIG. 2E is applied to the analog switch 36. Thereby, the tuning voltage applied to the varicap of tuner 16 increases by 10 volts with each sweep.
The signal shown in Figure 2 changes from volt, 20 volt, 30 volt, 10 volt, etc. For a tuning voltage of 10 volts, a tuning frequency response around 540 KHz (first waveform in Figure 2) appears on the tube surface of the oscilloscope 20, and for a tuning voltage of 20 volts, a tuning frequency response around 1100 KHz ( Figure 2 G-2
waveform), for a tuning voltage of 30 volts
A tuning frequency characteristic around 1650KHz (third waveform in Figure 2) appears. The frequency of the sweep drive sawtooth wave shown in FIG. Therefore, when tuning the tuner 16, the tuning of 540KHz, 1100KHz and 1650KHz is achieved by adjusting the coils of the three tuning circuits.
The influence on the three tuning point characteristics is obvious at a glance,
It is possible to simultaneously observe whether the tuning point of each tuning frequency characteristic is at a predetermined position on the tube surface.

The following modifications can be made to the present adjustment device described above. If necessary, the number of tuning adjustment points can be increased to four or more, in which case the number of variable resistors and analog switches can be increased by the increase in the number of adjustment points, and the reset of the decimal counter can be changed. Furthermore, the order in which the tuning voltage changes is not limited to the illustrated order. Further, although the tuning voltage is changed every time a sweep is made, it is possible to change the tuning voltage every two sweeps or more. However, in relation to the frequency of the sweep driving sawtooth wave, the waveform displayed on the screen must be at a level that does not flicker. The switching circuit uses a decimal counter in this device, but
Those skilled in the art can easily change to other circuits.

As described above, the present invention enables voltage variable capacitance diodes such as sweep oscillators, devices that generate multiple tuning voltages, and variable caps included in the tuning circuit of the tuner under test to be set to one of multiple tuning voltages for each sweep. It consists of a switching device that switches sequentially, and a device that detects the tuned frequency characteristics of the tuner under test and displays it on an oscilloscope. As a result, multiple tuning frequency characteristics with different tuning points can be observed simultaneously.
To enable tuning adjustment to be performed easily and quickly.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the tuning adjustment device of the present invention, and FIG. 2 is a waveform diagram for explaining the operation of the device shown in FIG. Description of symbols, 10...Sweep oscillator, 12...Switching circuit, 14...Tuning voltage generator, 16...Tuner, 18...Detector, 20...Oscilloscope,
22, 24, 26...variable resistor, 32, 34,
36...Analog switch.

Claims (1)

[Claims for Utility Model Registration] A tuning adjustment device for an electronically tunable tuner including a voltage variable capacitance element in a tuning circuit, comprising: (a) generating a sweep signal of the reception frequency of the tuner and applying it to the antenna input of the tuner; an oscillator, (b) a device that generates a plurality of tuning voltages, (c) a device that detects and displays the tuning frequency characteristic of the tuner when the tuning voltage is applied to the voltage variable capacitance element, and (d) a switching device that sequentially switches the tuning voltage applied to the voltage variable capacitance element to one of the plurality of tuning voltages for each sweep of the sweep oscillator, thereby making it possible to observe a plurality of tuning frequency characteristics at the same time. Tuner's tuning adjustment device.