JPS6134763Y2 - - Google Patents

Description

[Detailed explanation of the invention] In general, when receiving amplitude modulated signal AM broadcasting, a lower side wave detection signal or an upper side wave detection signal is selectively obtained, and interference such as beats from adjacent stations is effectively prevented. AM receivers are known.

The present invention is an AM that can selectively obtain such a lower side wave detection signal or an upper side wave detection signal.
The receiver is designed to perform particularly good AM demodulation.

The present inventors have proposed a conventional AM receiver as shown in FIG. 1 which selectively obtains a lower side wave detection signal or an upper side wave detection signal.
That is, in Fig. 1, 1 indicates an antenna for receiving AM broadcast signals, and the AM signal obtained by this antenna 1 is
The broadcast signal is sent to the mixing circuit 3 via the high frequency amplification circuit 2.
The output signal of the local oscillation circuit 4 is also supplied to the mixing circuit 3, and an intermediate frequency signal with a center frequency (carrier signal) of 450 kHz is obtained on the output side of the mixing circuit 3. It is supplied to the amplifier circuit 5.

Further, the output side of the intermediate frequency amplification circuit 5 is connected to the movable contact 6a of the first switch 6, and the lower side wave fixed contact 6L of the first switch 6 is connected to the carrier wave signal as shown in FIG. Connected to the input side of a lower side wave band pass filter 10 that passes 450 KHz and lower side wave signals (for example, a band pass filter with a passing center frequency of 445 KHz and passing signals in the frequency range of 440 kHz to 450 kHz). At the same time, this lower side wave fixed connection 6L is connected to the upper side wave fixed contact 7U of the third switch 7, and the upper side wave fixed contact 6U of this first switch 6 is as shown in FIG. 2E. Connected to the input side of an upper side wave band pass filter 11 (for example, a band pass filter whose passing center frequency is 455 kHz and which passes signals in the frequency range of 450 kHz to 460 kHz) that passes a carrier wave signal, e.g., 450 kHz, and an upper side wave signal. At the same time, this upper side wave fixed contact 6U is connected to the lower side wave fixed contact 7L of the third switching device 7, and the lower side wave band pass filter 10
The output side is the fixed contact 8 for the lower end wave of the second switch 8.
L and is also connected to the upper side wave fixed contact 9U of the fourth switch 9, and the output side of the upper side wave bandpass filter 11 is connected to the upper side wave fixed contact 8U of the second switch 8. and the fourth switch 9
The movable contact 8a of the second switch 8 is connected to the movable contact 7a of the third switch 7 via the buffer amplifier circuit 12, and the fourth switch 9 The movable contact 9a is connected to one input terminal of the multiplication circuit 14 via the phase adjustment circuit 13, and the movable contact 8a of the second switch 8
a is connected to the other input terminal of the multiplication circuit 14. In this case, the movable contacts 6a, 8a of the first, second, third and fourth switching devices 6, 8, 7 and 9,
7a and 9a are arranged to interlock with each other.
That is, when obtaining a lower side wave detection signal, the movable contacts 6a, 8a, 7a, and 9a are connected to the lower side wave fixed contacts 6L, 8L, 7L, and 9L, respectively, and when obtaining an upper side wave detection signal, Equal movable contact 6
a, 8a, 7a and 9a are connected to upper side wave fixed contacts 6U, 8U, 7U and 9U, respectively.

The output signal of this multiplier circuit 14 is sent to the speaker 1 via a low-pass filter 15 and an output amplification circuit 16.
7.

Next, to explain the operation shown in FIG. 1, when obtaining the lower side wave detection signal, the movable contacts 6a of the first, second, third and fourth switching devices 6, 8, 7 and 9,
8a, 7a, 9a are lower side wave fixed contacts 6L,
Connected to 8L, 7L and 9L. In this case, when an amplitude modulated signal (1+mcospt)cosωt is obtained on the output side of the intermediate frequency amplification _circuit 5, for example as shown in FIG. Since the bandpass filter 10 for lower side waves has a signal passing characteristic as shown in FIG. As shown in B, the signal cos is the sum of the carrier signal and the lower side signal.
ωt+m/2cos(ω-p')t is obtained, and this signal is supplied to the other input terminal of the multiplier circuit 14, and this signal cosωtm/2cos(ω-p')t is as shown in FIG. 2E. Since the signal is supplied to the upper side wave band pass filter 11 having signal passing characteristics, the lower side wave signal m/2cos(ω-p')t is output from this signal to the output side of the upper side wave band pass filter 11. A signal containing only the carrier wave signal cosωt as shown in FIG.
3 to one input terminal of the multiplier circuit 14, a lower side wave detection signal mcosp't is obtained at the output side of the low-pass filter 15, and this is reproduced by the speaker 17. Therefore, it is possible to reproduce a signal without a beat caused by the interference signal _fs .
Here, 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, and t is time.

Also, when obtaining the upper side wave detection signal, the first, second,
The movable contacts 6a, 8a, 7a and 9a of the third and fourth switching devices 6, 8, 7 and 9 are connected to the upper side wave fixed contacts 6U, 8U, 7U and 9U, respectively. In this case, since the upper side wave band pass filter 11 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 side wave signal, is obtained, and this signal is supplied to the other input terminal of the multiplier circuit 14, and this signal cosωt+
Since m/2cos(ω+p)t is supplied to the lower side wave band pass filter 10 having the signal passing characteristic as shown in FIG. The upper side wave signal m/2 cos(ω+p)t is removed from the signal to obtain only the carrier wave signal cosωt as shown in FIG. Since it is supplied to one input terminal,
An upper side wave detection signal mcospt is obtained at the output side of the low-pass filter 15, and this is reproduced by the speaker 17.

Accordingly, according to FIG. 1, the lower side wave detection signal or the upper side wave detection signal can be arbitrarily selected by simply switching the switchers 6, 8, 7 and 9.

However, in FIG. 1, when the modulation frequency is low (p-p' is small), the frequency pass characteristics of the bandpass filters 10 and 11 for lower side waves and upper side waves are not sharp, so the sideband waves cannot be sufficiently filtered. Therefore, the carrier wave signal for demodulation obtained at the output side of the series circuit of the lower side wave and upper side wave band pass filters 10 and 11 contains an amplitude modulation component. As shown in , the suppression ratio of the upper side wave signal and the lower side wave signal deteriorates by the amount a that the carrier signal is attenuated compared to the upper side wave signal and the lower side wave signal, causing the inconvenience that good AM demodulation cannot be performed. At the same time, when the electric field of the received broadcast is weak and the level of the carrier wave signal for demodulation obtained at the output side of the series circuit of the lower side wave and upper side wave band pass filters 10 and 11 becomes lower than a predetermined value, it is a good condition. There was an inconvenience that AM demodulation was not performed.

In view of this point, the present invention is designed to eliminate the above-mentioned drawbacks.

An embodiment of the AM receiver of the present invention will be described below with reference to FIG. In FIG. 3, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and detailed explanation thereof will be omitted.

In this example, the fourth switch 9 in FIG.
The signal output from the movable contact 9a is supplied to the phase adjustment circuit 13 via the phase lock loop circuit 20. The rest of the structure is the same as in FIG. 1.

That is, the phase lock loop circuit 20 is provided as a carrier wave signal extraction circuit for suppressing side wave signal components from a carrier wave signal including side wave signal components and emphasizing only the carrier wave signal.

Therefore, when receiving, the movable contact 9a of the fourth switch 9
A carrier wave containing a sidewave signal component outputted from the carrier wave passes through this phase lock loop circuit 20, so that the sidewave signal component is suppressed, and conversely, the carrier wave is emphasized. Only this carrier wave is phase-adjusted by a phase adjustment circuit 13 and then supplied to one input terminal of a multiplication circuit 14 serving as a detection circuit.

As described above, according to the present invention, the demodulation signal supplied to one input terminal of the multiplication circuit 14 is obtained via the carrier signal extraction circuit. For this purpose, the filters 10 and 1 remove interference such as beats generated when the lower side wave signal and the upper side wave signal are supplied to the multiplier circuit 14.
This can be prevented without depending on the so-called shoulder characteristic of No. 1, and good AM demodulation can be performed.

Furthermore, even when the level of the carrier wave signal of the output signal of the series circuit of filters 10 and 11 is low, such as when the electric field of the received broadcast is weak, since the carrier wave signal is passed through the carrier wave signal extraction circuit 20, one input terminal of the multiplier circuit 14 Since the level of the supplied carrier wave signal for demodulation can be maintained at a constant high level, good AM demodulation is possible.

Furthermore, when the lower side wave signal and the upper side wave signal occurring on both sides of the carrier wave signal have different levels, that is, are phase modulated, such a phase modulation component cannot be removed by using a limiter, but as in the present invention, the carrier wave signal This can be removed by using the extraction circuit 20.

Furthermore, since the carrier signal extraction circuit 20 has an AM suppressing effect, the low frequency modulation components inside the filters 10 and 11 can also be detected by the AM, and low frequency demodulation is also possible.

[Brief explanation of drawings]

Figure 1 is a configuration diagram showing an example of a conventional AM receiver.
Figure 2 is a diagram for explanation, Figure 3 is the AM of the present invention.
FIG. 1 is a configuration diagram showing an example of a receiver. 5 is an intermediate frequency amplification circuit, 10 is a lower side wave band pass filter, 11 is an upper side wave band pass filter,
6, 7, 8 and 9 are switchers, 15 is a band pass filter, and 20 is a carrier signal extraction circuit.

Claims (1)

[Scope of utility model registration request] It consists of a first band pass filter for passing the carrier wave signal and the lower side wave signal, a second band pass filter for passing the carrier wave signal and the upper side wave signal, and a phase lock loop, and suppresses the side wave signal component. A carrier wave signal extraction circuit for emphasizing only a carrier wave signal, a multiplication circuit for detecting a side wave signal, and a switching means for supplying an upper side wave signal or a lower side wave signal to the multiplication circuit, When the switching means is set to the first state, the amplitude modulated signal output from the intermediate frequency amplification circuit is sequentially passed through the first bandpass filter, the second bandpass filter, and the carrier signal extraction circuit to the above-described carrier wave signal extraction circuit. When the output signal from the first bandpass filter is supplied to the multiplication circuit and the lower side wave signal is detected, and the switching means is set to the second state, The amplitude modulation signal output from the intermediate frequency amplification circuit is sequentially supplied to the multiplication circuit via the second bandpass filter, the first bandpass filter, and the carrier signal extraction circuit, and is also supplied from the second bandpass filter to the multiplication circuit. A radio receiver in which an output signal of is supplied to the multiplication circuit and an upper side wave signal is detected.