JPS6117640Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an AM receiver, and more particularly to an AM receiver capable of selectively detecting and receiving the lower sideband or upper sideband of AM broadcasting.

In a conventional AM receiver, it is common practice to detect an intermediate frequency signal and use the detected signal to control various functions of the receiver, such as a synthesizer function and a muting function. This is one example.

In Figure 1, 1 indicates an antenna for receiving AM broadcast signals, and the
The AM broadcast signal is supplied to the mixing circuit 3 via the high frequency amplifier circuit 2, and the output signal of the local oscillation circuit 4 is supplied to the mixing circuit 3, and the center frequency (carrier signal) is output to the output side of the mixing circuit 3, for example. Obtain a 450kHz intermediate frequency signal, supply this intermediate frequency signal to an intermediate frequency amplifier circuit 5 for amplification, then supply it to a detection circuit 7 through a bandpass filter 6 to extract an audio frequency signal, and output amplify this audio frequency signal. The sound is amplified by the circuit 8 and emitted from the speaker 9.

On the other hand, the output signal of the intermediate frequency amplification circuit 5 is supplied to a narrowband wave detector 10 to extract a signal of a predetermined bandwidth, for example, 2 to 3 kHz, including the carrier wave signal, and this signal is supplied to a carrier wave detector 11 to generate a carrier wave signal. Obtain the DC signal related to. This DC signal is then supplied as a control signal to the synthesizer circuit 12 and also to the muting circuit 13. The synthesizer circuit 12 confirms that a certain broadcast wave has been caught by the supplied DC signal, stops the control operation of the local oscillation circuit 4, etc., and ends the automatic channel selection operation. Further, the muting circuit 13 which receives the control signal from the carrier wave detector 11 deactivates the output amplifying circuit 8 so as not to output the output signal when a certain broadcast wave is not caught, such as during tuning. When a broadcast radio wave is caught, a carrier wave detector 11 supplies a DC signal related to the carrier wave, and when the DC signal exceeds a predetermined level, the output amplifier circuit 8 is energized to send out an output signal. In other words, the muting circuit 13 is
Here, it works to prevent inter-station noise and suppress the emission of broadcast waves with weak electric field strength.

By the way, when the output signal of the carrier wave detector 11 is used as a control signal for the synthesizer circuit 12, etc., as described above, depending on the field strength of the broadcast radio waves during automatic channel selection, a malfunction may occur in which scanning stops at one step of a predetermined station. In order to prevent this, the narrower the passband width of the narrowband waveform waver 10, the better.

Therefore, in the case of a circuit configuration as shown in FIG. 1, if a narrowband transducer 10 is used, it becomes more expensive, and if a cheaper one is used, the performance must be sacrificed to some extent, which is an inconvenience. It was hot.

In view of this, the present invention has been designed to selectively detect and receive the lower sideband or upper sideband of AM broadcasts in order to effectively prevent interference such as beats from adjacent stations.
The present invention uses an AM receiver to eliminate the above-mentioned drawbacks and provides a high-performance, inexpensive AM receiver.

An embodiment of the present invention will be described in detail below with reference to FIGS. 2 and 3.

FIG. 2 shows a circuit configuration of an embodiment of the present invention. In FIG. 2, parts corresponding to those in FIG. 1 are given the same reference numerals, and detailed explanation thereof will be omitted.

In FIG. 2, the output side of the intermediate frequency amplification circuit 5 is connected to the movable contact 20a of the first switch 20, and the lower sideband fixed contact 20L of the first switch 20 is connected to the third A bandpass filter 24 for the lower sideband that passes the carrier signal and the lower sideband signal as shown in Figure D.
(For example, if the passing center frequency is 455kHz, 440kHz~
This lower sideband fixed contact 21L is connected to the upper sideband fixed contact 21U of the third switch 21. , the upper sideband fixed contact 20U of this first switch 20 is shown in FIG. 3E.
Input of an upper sideband bandpass filter 25 that passes the carrier signal and the upper sideband signal as shown in (for example, a bandpass transducer with a passing center frequency of 455kHz and passing signals in the frequency range of 450kHz to 460kHz). This upper sideband fixed contact 2
0U is the lower sideband fixed contact 2 of the third switch 21
1L, and connect the output side of the lower sideband waveband transducer 24 to the lower sideband fixed contact 22 of the second switch 22.
L and connected to the upper sideband fixed contact 23U of the fourth switch 23, and the output side of the upper sideband band waver 25 is connected to the upper sideband fixed contact 22U of the second switch 22. It is connected to the lower sideband fixed contact 23L of the fourth switch 23, and the second
The movable contact 22a of the switch 22 is connected to the movable contact 2 of the third switch 21 via the buffer amplifier circuit 26.
1a, and the movable contact 23 of the fourth switch 23
a to one input terminal of the multiplier circuit 28 via the phase adjustment circuit 27, and the second switch 2
The second movable contact 22a is connected to the other input terminal of the multiplier circuit 28. In this case, the movable contacts 20a, 22a, 21a and 23a of the first, second, third and fourth switching devices 20, 22, 21 and 23 are interlocked with each other. That is, when obtaining the lower sideband detection signal, the movable contacts 20a, 22a, 21a, and 23a are replaced with the lower sideband fixed contacts 20L, 22, respectively.
When connecting to L, 21L and 23L and obtaining the upper sideband detection signal, the movable contacts 2
0a, 22a, 21a and 23a are connected to upper sideband fixed contacts 20U, 22U, 21U and 23U, respectively.

The output signal of this multiplier circuit 28 is passed to a low frequency filter 29.
and is supplied to the speaker 9 via the output amplification circuit 8.

The operation of FIG. 2 will be explained below. When obtaining the lower sideband detection signal, the movable contacts 20a, 22a, 21a of the first, second, third and fourth switching devices 20, 22, 21 and 23, 23a are connected to lower sideband fixed contacts 20L, 22L, 21L and 23L, respectively. In this case, on the output side of the intermediate frequency amplification circuit 5, there is an amplitude modulated signal (1+mcospt) cosωt, that is, cosωt+m/2cos (ω+p)t+m, in which the interference signal f _S of the adjacent station exists in the vicinity of the upper sideband signal as shown in FIG. 3A, for example. /2cos(ω-p')t (where m is the modulation degree, p is the angular frequency of the upper sideband signal, p' is the angular frequency of the lower sideband signal, ω is the angular frequency of the carrier signal, t is time), the output side of the lower sideband waveband transducer 24, that is, since the lower sideband waveband transducer 24 has a signal passing characteristic as shown in FIG. 3D. The movable contact 22a of the second switch 22 receives a signal cosωt+m/2cos(ω-p')t, which is the sum of the carrier signal and the lower sideband signal, as shown in FIG. 3B, and this signal is multiplied. The signal cosωt+m/2cos(ω-p')t is supplied to the other input terminal of the circuit 28, and the signal cosωt+m/2cos(ω-p')t is supplied to the upper sideband bandpass filter 25 having the signal passing characteristic as shown in FIG. 3E. So,
On the output side of the upper sideband waveband transducer 25, there is a signal containing only the carrier wave signal cosωt, as shown in FIG. Since this carrier wave signal cosωt is supplied to one input terminal of the multiplier circuit 28 via the phase adjustment circuit 27, a lower sideband detection signal mcosp′t is obtained at the output side of the low frequency converter 29. The sound is emitted by the speaker 9. Therefore, the interference signal f
It is possible to play a signal without a beat by _S.

When obtaining the upper sideband detection signal, the movable contacts 20a, 22a, 21a and 23a of the first, second, third and fourth switching devices 20, 22, 21 and 23 are fixed for upper sideband. Contacts 20U, 22
Connect to U, 21U and 23U. In this case, since the upper sideband waveband transducer 25 has a signal passing characteristic as shown in FIG. A signal cosωt+m/2cos(ω+p)t, which is the sum of the carrier signal and the upper sideband signal, is obtained at 22a, and this signal is supplied to the other input terminal of the multiplier circuit 28, and this signal cosωt+m/2cos(ω+p) t is supplied to the lower sideband waveband transducer 24 having signal passing characteristics as shown in FIG. A signal containing only the carrier wave signal cosωt as shown in FIG. As a result, an upper sideband detection signal mcospt is obtained at the output side of the low frequency filter 29, and this is emitted by the speaker 9.

Therefore, by simply switching the switches 20, 22, 21 and 23, the lower sideband detection signal or the upper sideband detection signal can be arbitrarily selected.

Further, in FIG. 2, on the output side of the multiplier circuit 28, a DC detecting means, for example, a low frequency filter 30, for detecting a DC signal from the output signal of the multiplier circuit 28 is provided.
The low-pass filter 30 is set to extract only the DC component, whereas the low-pass filter 29 extracts the audio frequency component.

When the lower sideband detection signal or the upper sideband detection signal is obtained on the output side of the multiplier circuit 28 as described above, only the DC component of these detection signals supplied to the low frequency filter 30 is extracted. For example, when receiving the lower sideband, a signal of 2/1(cos2ωt+cos0)+m/4 {cosp′t+cos(2ω−p′)t} is obtained at the output side of the multiplier circuit 28, so this signal is By passing it through the wave generator 30, 2/1 cos0 = 1/
2. In other words, only the DC component is extracted.

This DC signal is supplied to the synthesizer circuit 12 and the mutating circuit 13 and controls these circuits as described above.

The common part of the two band wave generators 24 and 25 whose center frequencies are characteristically shifted constitutes a narrow band wave wave generator with an extremely narrow bandwidth of, for example, 1 to 2 kHz. It is possible to obtain a highly accurate control signal on the output side that does not cause the above-mentioned scanning stop malfunction.

As described above, according to the present invention, the DC component is detected by the signal detected in the lower sideband or upper sideband of AM broadcasting, and the specific functions of the receiver are controlled. When controlling, it is possible to prevent malfunctions such as stopping scanning before one step using an inexpensive configuration, and extremely accurate control is possible using a DC signal based on a detection signal obtained through a narrow band, and the configuration is simple. It's cheap.

In the above-described embodiments, the case where a synthesizer circuit or a muting circuit is controlled by the DC signal obtained at the output side of the low frequency converter 30 has been explained, but the present invention is not limited to this, and circuits having other functions may also be used. may be controlled.

Further, although the case where a low-band filter is used as the DC detection means has been described, other means may be used as long as the DC component can be extracted from the sideband detection signal.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing an example of a conventional AM receiver.
FIG. 2 is a block diagram showing an embodiment of the AM receiver of the present invention, and FIG. 3 is a diagram for explaining the operation of FIG. 5 is an intermediate frequency amplifier circuit, 12 is a synthesizer circuit, 13 is a mutating circuit, 20, 21, 2
Reference numerals 2 and 23 designate a frequency converter, 24 a band waver for the lower sideband, 25 a band waver for the upper sideband, 28 a multiplier, and 30 a low band waver.

Claims (1)

[Scope of utility model registration request] a first band waver that passes the carrier signal and the lower sideband signal; a second band waver that passes the carrier signal and the upper sideband signal; a switching means for connecting the first and second band wave transducers in series in the order of the first and second band wave transducers, and a multiplier circuit for connecting the second and first band wave transducers in series in the second state. and the amplitude modulation signal of the output of the intermediate frequency amplification circuit is supplied to the series circuit of the first and second bandpass amplifiers, and the output signal of the series circuit is supplied to the multiplication circuit, When the switching means is in the first state, the output signal of the series circuit and the output signal of the first bandpass filter are supplied to the multiplier circuit to obtain a lower sideband detection signal, and the lower sideband detection signal is obtained. The switching means is the second
When the output signal of the series circuit and the second
In the AM receiver, a DC signal is detected from the output signal of the multiplier circuit on the output side of the multiplier circuit, in which the output signal of the band waver is supplied to the multiplier circuit to obtain an upper sideband detection signal. 1. An AM receiver characterized in that a DC detection means is provided, and various functions of the receiver are controlled by the detected DC signal.