JPS59168785A - Magnetic picture recording and reproducing device - Google Patents

Abstract

PURPOSE:To obtain easy to see picture with less noise even at a weak electric field by changing the resistance value of an emphasis circuit with an IF.AGC voltage so as to change automatically the frequency characteristic of a luminance signal system at recording. CONSTITUTION:The IF.AGC voltage in an intermediate frequency amplifier circuit is applied to base of a transistor (TR)17. SInce the IF.AGC voltage is at a low level at a strong electric field, the TR17 is turned off and a TR18 is turned on. As the electric field becomes weaker, the IF.AGC voltage is increased gradually, then the TR17 starts to turn on and the ON-resistance of the TR18 is increased. Thus, the amount of emphasis depends on the value of a resistor 22 at a strong electric field and on sum of the resistor 22 and the ON-resistance of the TR18 at a weak electric field. Thus, a picture having a good S/N is obtained even at a weak electric field.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic recording and reproducing apparatus having a tuner for receiving a television signal to be recorded.

Conventional Structure and Its Problems FIG. 1 shows the structure of a recording system of a conventional magnetic recording/reproducing apparatus having a tuner. In FIG. 1, 1 is an antenna for receiving radio waves, and 2 is a tuner for selecting programs. 3 is an intermediate frequency amplification circuit, which increases the received signal frequency by about half (68
, 75 mHz) and amplified, and a video signal and an audio signal are extracted by a video detection circuit 4 and an audio detection circuit 5. The audio signal is then transferred to the audio signal system (not shown).
After processing, the signal is supplied to an audio head (not shown) K. The video signal is divided into a chroma signal and a luminance signal, and the chroma signal is processed by six chroma signal systems. The brightness signal is kept constant at 1 novel by 7 A10 circuits, and 8
A low-pass filter removes excess high-frequency components. Reference numerals 9 and 10 are a non-linear effect circuit and an effect circuit, which process signals during recording and reverse processing during playback, thereby improving the custom frequency. 11 is an FM modulation circuit that performs FM modulation on the emphasized luminance signal, and after removing unnecessary low-frequency signals with an I-pass filter 12, the chroma signal system 6
is combined with the chroma signal processed by

An amplifier circuit 13 amplifies the combined chroma signal and luminance signal, and the signals are recorded on a magnetic tape (not shown) from a video head 14.

Here, the conventional emphasis circuit 1o is generally constituted by a series circuit of a capacitor 15 and a resistor 16 as shown in FIG. However, since the capacitance and resistance values of this circuit are constant, the frequency must be custom-made or fixed regardless of the strength of the electric field, and noise becomes noticeable on the screen in weak electric fields. For this reason, in the past, an image quality adjuster was set up to change the upper value or resistance value of the capacitor 11, and in regions with weak electric fields, the custom frequency was lowered to reduce the S/N.
However, this method has the disadvantage that adjustments must be made each time.

OBJECTS OF THE INVENTION In view of the above-mentioned drawbacks, the present invention provides an inexpensive magnetic recording and reproducing device that is capable of automatically recording and reproducing images with less noise and easy to see even when the electric field strength changes.

Structure of the Invention In order to achieve this object, the present invention focuses on IF-AGC in an intermediate frequency amplifier circuit: this IF-A that focuses on voltage.
The G[voltage is the voltage required to operate the circuit (IF/AGO circuit) that maintains the video detection output level at a constant level even in a weak electric field, and its custom-made is generally made when the input electric field is approximately Is it constant above 66aBμ?55
(Below IBμ, it begins to rise. In the present invention, this step) This system automatically changes the frequency characteristics of the luminance signal system to obtain an easy-to-see image with little noise even in areas with weak electric fields.

DESCRIPTION OF THE EMBODIMENT FIG. 4 shows a main part of an embodiment of the present invention, and this embodiment has a configuration in which the resistance value within the emphasis circuit is changed. In this circuit, resistors 19, 20.2
By appropriately determining the constant of 1 and applying the IF-AC÷C voltage to the base of the transistor 170 as shown in FIG.
In a strong electric field, the IF and AGC voltages are at LOW level, so transistor 17 is OFF, and transistor 18 is OFF.
It becomes N.

Next, as the electric field becomes weaker, the I F -AGq voltage gradually increases, so the transistor 17 starts to turn on, and the base potential of the transistor 18 starts to decrease by 1, so the ON resistance of the transistor 18 increases. Also, resistance 19,
The constant 20.21 is determined so that the S/N ratio of the image does not deteriorate in a weak electric field, and the emphasis amount is such that an appropriate frequency characteristic can be obtained in a normal electric field or higher. With the above configuration, the transistor 18 is completely turned on in a weak electric field, so the amount of activation is determined by the value of the resistor 22, and in a weak electric field, it is determined by the sum of the ON resistance of the resistor 22 and the transistor 18. . Therefore, in a strong electric field, the resistance value is small, so the amount of emphasis increases and the frequency characteristics improve. Also, in a weak electric field, the resistance value increases, so the amount of emphasis decreases, and the frequency 4? Notes are reduced, but the S/N on the screen is improved. By using the IF-AGO voltage in this manner, it is possible to obtain an emphasis amount that corresponds to the electric field strength, and it is possible to obtain an easy-to-see image with a good S/N ratio even in a weak electric field.

In the embodiment, the resistance value in the emphasis circuit is changed, but the same effect can be obtained by changing the capacitance value.

Furthermore, it is possible to completely change the frequency characteristics using the F-AGC voltage not only during recording but also during reproduction.

Effects of the Invention As described above, according to the present invention, since the amount of emphasis is automatically changed according to the electric field strength, it is possible to record and reproduce video signals that are easier to see.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the recording system of a magnetic recording/reproducing device having a tuner, and Fig. 2 is an IF-
A diagram showing the relationship between AGC voltage and electric field strength, FIG. 3 is an electric circuit diagram showing an example of a conventional emphasis circuit, and FIG. 4 is an electric circuit showing essential parts of an embodiment of the magnetic recording and reproducing apparatus of the present invention. It is a diagram. 1 Dad'' antenna, 2゛...tuner, 3°...
...Intermediate frequency amplification circuit, 4...Video detection circuit, 5...Audio detection circuit, 6...Parchroma signal system, 7...AGO [ill, 8 ...Low pass filter, 9...No, linear effect 7
cis circuit, 1o-=-emphasis circuit, 11...
・FM modulation circuit, 12 pass bypass filter, 13...
...Amplification circuit, 14...Video head. Name of agent: Patent attorney Toshio Nakao and 1 other person 2 Figure 4

Claims (1)

[Claims] Recording the video signal from the tuner receiving the television signal to be recorded via a custom-made circuit whose frequency varies according to the AGO voltage in an intermediate frequency amplification circuit to which the output of the tuner is applied. A magnetic recording and playback device featuring