JPH0241951Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] This invention relates to a superheterodyne FM receiving device that receives audio signal waves of FM broadcast waves in the VHF band and television broadcast waves in the VHF band and UHF band. .

[Conventional technology] Conventionally, FM broadcast waves in the VHF band,
When receiving audio signal waves of UHF band television broadcast waves, as shown in Fig. 2, each dedicated front end 1a, 1b, 1c is switched,
An intermediate frequency signal with a center frequency of 10.7MHz (hereinafter referred to as IF signal) or audio intermediate frequency signal (hereinafter referred to as SIF signal)
signal) and converts it into an intermediate frequency amplification circuit (hereinafter referred to as
The audio signal is amplified by an IF amplification circuit 2a (referred to as an IF amplification circuit), and an audio signal is obtained via an FM detection circuit 3a, an FM demodulation circuit 8, and an audio amplification circuit 6.

Note that 4a is a tuning detection circuit that detects tuning using a signal from the FM detection circuit 3a, and 7 is an optical display circuit that displays tuning using the output of the tuning detection circuit 4a.

[Problems to be solved by the invention] This type of conventional FM receiver has an advantage in terms of cost because it uses the IF amplifier circuit 2a in common, but it has an advantage in terms of cost because it uses the IF amplifier circuit 2a in common. Broadcast waves in the VHF band of 90~222MHz and 470~
When adopting the superheterodyne method that converts the 770MHz UHF band into a fixed IF signal, for example, an IF signal with a center frequency of 10.7MHz, the VHF band and
The tuning frequency bandwidth of the front end for UHF band tervision broadcast waves has become wider, and if there is even a slight nonlinearity in the front end, a large number of image signal interference waves will be generated due to that nonlinearity. There was a problem in which it was difficult to tune in because it was not possible to determine which wave was a broadcast wave.

[Means for solving the problem] This invention is aimed at avoiding the reception of interference waves of the image signal, and as shown in the embodiment of FIG.
In a superheterodyne FM receiving device that converts the audio signal waves of television broadcasts in the VHF band and UHF band into the same intermediate frequency signal and demodulates the same intermediate frequency signal, when reproducing the audio signal waves of the television broadcasts, the video signal from audio intermediate frequency to 4.5M
This is an FM receiver that converts into a video intermediate frequency signal separated by Hz, detects the presence or absence of tuning, and displays an optical display when both the audio intermediate frequency signal and the video intermediate frequency signal are tuned.

[Example] In Fig. 1, 1a, 1b, 1c are respectively
FM, VHF and UHF front ends, S ₁ and S ₂
are switches for selecting one of the front ends, 2a is an SIF amplifier circuit, 3a is an FM detection circuit, 8 is an FM demodulation circuit, and 6 is an audio amplifier circuit. Also, 2b is a frequency 4.5MHz apart from the SIF signal, for example, in the case of the lower heterodyne, the center frequency is 6.2MHz compared to the SIF signal's center frequency of 10.7MHz.
Video intermediate frequency signal converted to the frequency band (hereinafter referred to as
PIF amplification circuit 3b that amplifies the PIF signal (referred to as PIF signal)
is an FM detection circuit, 4b is a tuning detection circuit,
After detecting the PIF, the synchronization signal is separated, and tuning is detected based on the presence or absence of the synchronization signal.

Further, 5 is a NAND circuit which receives the signals of the PIF signal and SIF signal tuning detection circuits 4b and 4a as input;
7 is an optical display circuit driven by the NAND circuit.

The operation will be explained below.

When tuning SIF signal, 10.7M of FM detection circuit 3a
A tuning bandwidth is defined as a predetermined band above and below Hz, and the tuning detection circuit 4a outputs a low level (hereinafter referred to as L level) when within this tuning bandwidth, that is, when tuned.

Also, when tuning the PIF signal, the FM detection circuit 3b
The tuning bandwidth is between a predetermined band above and below 6.2MHz, and when in this tuning bandwidth,
That is, when tuned, the tuning detection circuit 4b outputs an L level.

The NAND circuit 5 outputs an H level when the tuning detection circuits 4a and 4b are each at an L level, and lights up the light emitting diode 7.

This kind of circuit operation is based on the local oscillation frequency ( ₀ ) when receiving audio signal waves of television broadcast waves.
The explanation will be given using an example of sweeping from the lower side to the higher side. Note that the frequency of the audio signal wave is _s , and the frequency of the video signal wave is _p .

When _s − ₀ > 10.7 MHz _p − ₀ > 6.2 MHz, that is, when the detuning is to the lower side, the outputs of the tuning detection circuits 4a and 4b each go to H level, and the output of NAND circuit 5 goes to L level, causing light emission. Diode 7 is off.

When _s − ₀ = 10.7MHz _p − ₀ = 6.2MHz, that is, when the synchronization is accurate, the outputs of the tuning detection circuits 4a and 4b each become L level, the output of NAND circuit 5 becomes H level, and the light emitting diode 7 lights up. .

When _s − ₀ < 10.7MHz _p − ₀ < 6.2MHz, that is, when detuned to the higher side,
The outputs of the tuning detection circuits 4a and 4b are respectively H.
level, the output of the NAND circuit 5 becomes L level, and the light emitting diode 7 turns off.

In the case of ₀ − _s = 1.7MHz ₀ − _p = 6.2MHz, that is, for the image signal of the video signal wave, the output of the tuning detection circuit 4a is H level, the output of the tuning detection circuit 4b is L level,
The output of the NAND circuit 5 becomes L level and the light emitting diode 7 is turned off.

In the case of ₀ − _s = 10.7MHz ₀ − _p = 15.2MHz, that is, for the image signal of the audio signal wave, the output of the tuning detection circuit 4a is L level, the output of the tuning detection circuit 4b is H level, and the NAND
The circuit 5 output becomes L level and the light emitting diode 7
is off.

In this way, in the →→→→ operation, when only the broadcast wave is accurately received, the light emitting diode lights up to indicate tuning.

Incidentally, in the case of FM broadcast waves, reception is performed in the same manner as a conventional FM receiving device.

[Effects of the invention] The FM receiver of this invention is a component of an intermediate frequency amplification circuit that converts FM broadcast waves in the VHF band and audio signal waves of television broadcasts in the VHF and UHF bands into the same intermediate frequency and receives them. The number of points is reduced, and malfunctions due to image interference waves generated at the front end can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of this invention.
FIG. 2 is a block diagram of a conventional device. 1...Front end, 1a...Front end for FM broadcast waves, 1b...Television broadcast waves
Front end for VHF, 1c... Front end for television broadcast UHF, 2a... SIF amplifier circuit, 2b... PIF amplifier circuit, 3a, 3b...
FM detection circuit, 4a, 4b... Tuning detection circuit, 5
...NAND circuit, 6...Audio amplification circuit, 7...
Light emitting diode, 8... demodulation circuit.

Claims (1)

[Scope of utility model registration request] In a superheterodyne FM receiving device that converts FM broadcast waves in the VHF band and audio signal waves of television broadcasts in the VHF band and UHF band into the same intermediate frequency signal and demodulates the same, the audio signal wave of the television broadcast When playing, the video signal is converted to a video intermediate frequency signal that is 4.5MHz apart from the audio intermediate frequency, the presence or absence of synchronization is detected, and an optical display is displayed when both the audio intermediate frequency signal and the video intermediate frequency signal are synchronized. An FM receiving device characterized by: