JPH0448826A - Broadcast wave receiving device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a receiving device that receives television broadcasting, radio broadcasting, etc., and more specifically, a signal processing circuit that improves the S/N ratio when receiving a weak electric field. Regarding.

[Prior Art] Fig. 2 is a block diagram of a luminance signal processing circuit of a magnetic recording/reproducing device equipped with a conventional television receiver, where (+) is a television signal processing circuit, and (2) is a demodulated video signal. An AGC circuit to which the signal is input, (3) a clamp circuit that keeps the pedestal level of the video signal constant, and (4) an LPF that extracts only the luminance signal component Y from the video signal.
5) is an FM modulator that performs FM modulation on the luminance signal.

Next, the operation will be explained.

The television signal processing circuit (+) demodulates the received signal into a video signal. The AGC circuit (2) controls the signal to always be at a constant level depending on the level of the horizontal synchronization signal of the input video signal or the level of the entire video signal, and the clamp circuit (3) controls the signal in the signal processing process. The DC component of the video signal lost in the video signal is regenerated to correct the variation in the black level due to the average luminance level (APL) of the video signal.

L, P F (4) extracts only the luminance signal component Y, and the FM modulator (5) performs FM modulation on the input luminance signal and outputs an FM luminance signal. This FM luminance signal is subjected to signal processing for magnetic recording in a recording signal processing circuit (not shown) and then recorded on a magnetic tape.

[Problem to be solved by the invention J Since the conventional receiving device is configured as shown in 1 below,
When the electric field strength of the broadcast signal is weak, the SLN of the received signal decreases, and in a magnetic recording and reproducing device equipped with a television receiver, the SLN of the bidirectional video signal decreases, making it difficult to see the visual sense. There was a point.

This invention was made to solve the above-mentioned problems, and it is an object of the present invention to provide a receiving device that can improve the SlN of a received signal even when the electric field strength of a broadcast signal is weak.

[Means to solve problems]

The receiving apparatus according to the present invention includes means for reducing high frequency components of a received signal only when the electric field strength of the broadcast signal is weaker than a certain level.

[Operation J] Receiver 3 in this invention (means for reducing high-frequency components in item 3) detects when the electric field strength of a broadcast signal is weaker than a predetermined level and reduces the high-frequency components of the received signal. As a result, the noise component contained in the received signal is reduced, and the SIN is improved.

[Example] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block circuit diagram of this embodiment, and the same parts as in FIG. 2 are given the same reference numerals and their explanation will be omitted.

In the figure, (6) is the RF-AGC circuit in the television signal processing circuit m, and (7) is the RFAGC voltage V aac
A voltage comparator (8) is a variable frequency characteristic circuit that compares the output voltage V of the voltage comparator (7) with a reference value V3. It consists of a transistor Q to which ut is input to the base, and a capacitor C connected between the collector of the transistor Q and the input terminal of the FM modulator (5). 7. Next, the operation will be explained.

When the electric field strength of Television Broadcast No. 43 is weak.

The RF-AGC voltage vAGe has a high level inversely proportional to the electric field strength and is applied to one terminal of the voltage comparator (7).

Assuming that the reference voltage applied to the other ten terminals is Sl, when vAGc>vsI, V0LIL becomes "T- level", so it becomes equivalent to resistor R1 and R8 connected in parallel. < V s + = V s * (In the case of D, V out becomes "H", so it becomes equivalent to connecting resistors R and R3 in parallel. These two reference voltages V□ and vs- r is Vs
Since the relationship is + < V s□, the output voltage V a of the voltage comparator (7)
u, is the AGC voltage V AGC change (electric field strength change)
It has a hysteresis characteristic and is never unstable.

The output v0゜1 of this voltage comparator (7) is input to the frequency characteristic variable circuit (8), and when it is at "H" level, the transistor Q is turned on and the luminance signal Y is input to the FM modulator (5). ■When ut is at the "[," level, transistor Q is OFF and capacitor C is attenuated.
is blocked, and the brightness signal Y (7) does not change the frequency characteristics.

As described above, according to this embodiment, when the received electric field VTR strength becomes lower than a certain level, the output voltage V of the voltage comparator (7). When ut becomes "H" level, the noise component of the luminance signal is attenuated, and the electric field strength becomes high, the reference voltage vfil changes to Vs+→■3 with hysteresis characteristics.
The output voltage of the voltage comparator (7) changes to □. engineering, but “
[7'' level and eliminates the attenuation effect of the high-frequency components of the luminance signal Y, so it is possible to improve the S/N ratio of the received signal when receiving a weak electric field, and to reduce the deterioration of the high-frequency components when receiving a strong electric field. Therefore, a signal processing circuit without any noise can be obtained.

In addition, in the above embodiment, the case of improving the S/N of the brightness signal of a television receiver (TR with 14 units) was explained as an example, but it can be similarly applied to the television receiver itself or a radio receiver, etc. can.

[Effect of the invention] This invention provides an RF-AG that changes depending on the received electric field strength.
By comparing the C voltage signal and the reference voltage, the high-frequency components including noise components of the received signal are attenuated only when the electric field strength is lower than a predetermined level, so the S/N when receiving a weak electric field is reduced.
This has the effect of providing a broadcast wave receiving device that can improve the performance.

[Brief explanation of drawings]

1 is a block circuit diagram of an embodiment of the present invention, and FIG. 2 is a block circuit diagram showing a main part of a luminance signal processing circuit of a VTR equipped with a TV/vision receiver. (1)...prevision signal processing circuit, (4)...
11'! ”, (5)...FM modulator, AGC circuit,
(7)...Voltage comparator, gender variable circuit. In each figure, the same reference numerals indicate the same parts.

Claims (1)

[Claims] (1) A receiving device equipped with an AGC circuit that receives a broadcast radio signal and controls the gain of a high-frequency amplifier circuit so that the level of the received signal is constant, and the AGC voltage of the AGC circuit is adjusted in advance. It is characterized by comprising means for comparing with a reference voltage corresponding to a predetermined weak electric field level, and means for attenuating high-frequency components of the received signal only when the comparison result is a received electric field lower than the weak electric field level. Broadcast wave receiving device.