JPS6216048Y2 - - Google Patents

Description

[Detailed description of the invention] This invention obtains an angle modulated wave obtained by angle modulating (FM modulation or phase modulation) a carrier wave by a sub signal (L-R) signal and amplitude modulating it by a main signal (L + R) signal. receive AM stereo radio waves.
The present invention relates to an AM stereo receiver whose purpose is to eliminate beats that occur when the field strength of AM stereo radio waves becomes weak.

First, an overview of a conventional AM stereo receiving device will be explained.

Note that angle modulation usually includes FM modulation and phase modulation as described above, but here it is assumed that the carrier wave is FM modulated with an (L-R) signal,
A case will be described in which FM detection means is used as the angle detection means in the AM stereo receiver.

FIG. 1 is a block diagram of a decoder section (detection section) of a conventional AM stereo receiving device, and shows
1 is an AM detector as an amplitude detection means, 2 is an FM detector as an angle detection means, 3 is a matrix circuit, 4 is a sub-signal muting circuit, and 5 is a stereo pilot tone detection circuit.

Signal line A is the final output from the IF amplification stage (not shown) in the tuner section.
The IF signal (intermediate frequency signal) is input to the AM detector 1 and the FM detector 2 through the signal line A.

The above AM detector 1 consists of an AM detection circuit,
The main signal is demodulated from the IF signal.

In addition, the FM detector 2 has an amplitude limiting circuit and an FM detector.
It includes a detection circuit, and the above amplitude limiting circuit
In order to remove the amplitude component of the IF signal, the IF signal is amplitude limited to form a limiter waveform, and then,
The above IF signal having only frequency information is the above FM signal.
The detection circuit performs FM detection and demodulates it into a sub signal.

This demodulated sub-signal includes a stereo pilot tone, which is detected by the stereo pilot tone detection circuit 5 and transmitted through the stereo detection signal line C to the sub-signal muting circuit 4. will be introduced in

On the other hand, the output of the FM detector 2 is introduced into the matrix circuit 3 through the sub-signal muting circuit 4. In the matrix circuit 3 above,
As is well known, sum and difference calculations are performed using the (L+R) signal and the (L-R) signal, and these signals are
and R signals.

Signal line B is a forced monaural electric field strength signal output from a tuner section (not shown) and is introduced into the sub-signal muting circuit 4.

As mentioned above, the sub-signal muting circuit 4 is connected after the FM detector 2,
When the electric field strength becomes weak and no pilot tone is detected, or when the forced monaural electric field strength signal becomes less than a predetermined value, muting is activated and prevents the sub-signal from being introduced into the matrix circuit 3. It's summery.

By the way, in such a stereo receiving device,
The harmonics (for example, 900KHz, 1350KHz harmonics) of the IF signal (450KHz) whose amplitude is limited in the FM detector 2 and made into a limiter waveform are emitted into the air as radio waves by the FM detector 2, and the harmonics are Waves sometimes entered the AM stereo receiver through an antenna (not shown).

In such a case, the above harmonics are being received
Beats that occur between the frequency of AM stereo radio waves are a problem, but if the field strength of the AM stereo radio waves being received is strong enough, the amplitude of the AM stereo radio signal input to the antenna will be higher than the above harmonics. Since it is sufficiently larger than the amplitude, there is no problem with the beat described above.

However, as the electric field strength weakens and the amplitude of the AM stereo radio waves input from the antenna becomes smaller and becomes almost equal to the amplitude of the harmonics, as a result, the frequency of the AM stereo radio waves and the harmonics become smaller. The problem is that a loud beat occurs in the tuner section, the AM detector 1, and the matrix circuit 3, and is reproduced as noise from the speaker (not shown), making it impossible to listen to the broadcast with satisfactory reception conditions. The dot was hot.

This invention was made to improve the above problem, and when the electric field strength is weak, the IF signal is
To prevent it from being supplied to FM detector 2
A muting circuit is provided before the FM detector 2.

Hereinafter, one embodiment of the present invention will be described based on the drawings. Figure 2 is an AM diagram explaining an embodiment of the present invention.
FIG. 2 is a block diagram of a decoder section (detection section) of the stereo receiver.

In the figure, parts having the same functions as those of the conventional example described above are given the same numbers and detailed explanations will be omitted.

6 is connected to the front stage of the above FM detector 2.
It is an IF signal muting circuit and is connected to a signal line A that sends the final output from an IF amplification stage (not shown).

The forced monaural electric field strength signal line B from the tuner section (not shown) is introduced into the IF signal muting circuit 6 together with the sub signal muting circuit 4, and this forced monaural electric field strength signal is transmitted to a predetermined level. When the value falls below this value, the sub signal muting circuit 4 and the IF signal muting circuit 6 start operating at the same time.

Since the present invention is configured as described above, when the electric field strength becomes weak while receiving AM stereo radio waves, the IF signal muting circuit 6 uses the forced monaural electric field strength signal obtained from the tuner section.
and the sub-signal muting circuit 4 operate simultaneously to block input of the IF signal to the FM detector 2.

That is, the electric field strength becomes weaker, and the IF signal muting circuit 6 and the sub signal muting circuit 4
In the monaural state in which the FM detector 2 is operating, no IF signal is input to the FM detector 2.
No higher harmonics are emitted and no beats occur.

As described above, the present invention can be applied to the front stage of the angle detection means.
An IF signal muting means is provided, and when the field strength signal becomes less than a predetermined value based on the received broadcast radio wave, the muting means is operated to prevent the introduction of the IF signal to the angle detection means. Therefore, when the electric field strength is weakened, beats do not occur and the broadcast can be listened to with sufficient reception.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a decoder section of an AM stereo receiving apparatus showing a conventional example, and FIG. 2 is a block diagram of a decoder section of an AM stereo receiving apparatus showing an embodiment of the present invention. 1...AM detector, 2...FM detector, 3...matrix circuit, 4...sub signal muting circuit,
...IF signal muting circuit, 5...Stereo pilot tone detection circuit.

Claims (1)

[Claims for Utility Model Registration] AM stereo broadcast radio waves containing information signals of the sum and difference of L channel and R channel signals are received and converted into intermediate frequency signals, and amplitude detection means is used to calculate the above sum from the intermediate frequency signals. demodulating the information signal and demodulating the difference information signal using angle detection means;
These sum and difference information signals are processed by a matrix circuit.
AM separated into channel and R channel signals
In the stereo reception device, a muting means for mutating the intermediate frequency signal is provided before the angle detection means for demodulating the difference information signal, and a muting means for mutating the difference information signal is provided before the matrix circuit. An AM stereo receiving device characterized in that the above-mentioned muting means are both operated when the received field strength signal becomes less than a predetermined value.