JPS5852734Y2 - AM broadcast receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an AM broadcast receiver, and more particularly to a detection circuit for detecting the presence of broadcast waves on a receiving channel.

This detection circuit is used in automatic tuning equipment, especially digital tuning systems, etc., to detect the presence of broadcast waves on a receiving channel, and when a broadcast wave is applied to that receiving channel, the receiving frequency is automatically and sequentially changed to the next receiving channel. It is applied to the reception frequency adjustment mechanism of radio receivers, which automatically adjusts the reception frequency to the channel where the broadcast wave is present.

Since the broadcast frequency interval of AM radio broadcasting is very narrow, about 9 to 10 KHz, the frequency selection characteristic of the detection circuit is normally to use a steep and narrow band F wave detector to prevent malfunction due to signals of adjacent channels. The narrower the range, the lower the response speed and the more expensive the offshore wave device becomes.

An object of the present invention is to obtain a signal detection circuit, particularly an AM broadcast wave signal detection circuit, which has a fast response speed and is relatively inexpensive.

The detection circuit of the present invention has a configuration in which the received signal is limited in amplitude to a constant amplitude and then added to the bandpass filter, thereby obtaining a signal detection circuit with good frequency selection characteristics, fast response speed, and low cost. I can do it.

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

Figure 1 shows an embodiment of the present invention, in which A received by a tuner is
The M broadcast signal is applied to the limiter 1 from the input terminal 5 and is shaped to have a constant amplitude.

As the output of the limiter 1, a signal of the frequency currently being received is taken out by a narrowband waveformer 2, which is detected by a wave detector 3, DC amplified by a DC amplifier 4, and taken out from an output terminal 6.

The output thus taken out is applied to a device that, for example, shifts the receiving channel if the voltage is absent, and receives on that receiving channel if the voltage is present.

Next, the operation of the above-mentioned embodiment will be explained with reference to FIG. 2ab, assuming that there is no broadcast wave on the receiving channel and there is a broadcast wave on the adjacent channel.

Figure 2a shows the frequency energy distribution of the input signal when the receiving center frequency 21 is 450 KHz and the adjacent wave center frequency 22 is 460 KHz.First, the amplitude of the received signal is limited by the limiter 1, so The carrier component 22 of the adjacent channel signal is emphasized, and as a result, the sideband components 23 and 24' of the adjacent channel signal are relatively suppressed.

Therefore, as shown in Fig. 2, sideband components 23', 24
' becomes an extremely small frequency energy distribution, and only the carrier component 22 of the adjacent channel is emphasized and extracted.

Next, the carrier signal (460 KHz) 22 of the adjacent channel is attenuated by the narrowband filter 2 having a center frequency of 450 KHz.

The frequency selection characteristic of the narrow band wave filter 2 does not need to be so steep, and since the sideband components of the adjacent channel are sufficiently attenuated by the limiter 1, the frequency selection characteristic of the narrow band wave filter 2 is sufficiently attenuated, so that the carrier signal of the adjacent channel can be sufficiently attenuated, that is, from the center frequency. It suffices if it has frequency selection characteristics that can sufficiently attenuate components separated by 10 KHz or more.

In the case of FIGS. 2a and 2b, since the center frequency component 21 is zero, almost no signal component is supplied to the detector 3, so the detected output voltage becomes almost zero, and the output voltage of the DC amplifier 4 also becomes zero.

Next, assuming a situation where there is a broadcast wave on the receiving channel and no broadcast wave on the adjacent channel, an explanation will be given using FIGS. 3a and 3b.

The figure again shows the frequency energy distribution of the signal 31 when the reception center frequency is 450 KHz.

Since the carrier component 31 of the broadcast wave is emphasized by the limiter 1, the sideband components 33 and 34 are relatively suppressed, and the sideband components 33' and 34' become extremely small as shown in the figure.

Thereafter, only the carrier signal 31 of the broadcast wave is extracted by the 450 KHz narrow band transmitter 2.

In the detected broadcast wave signal, the carrier signal 31 is emphasized and the sideband components 33' and 34' are relatively suppressed, so the output of the detector 3 is a stable signal close to direct current with little temporal fluctuation. becomes.

Furthermore, as shown in Figures 2 and 3, when the AM broadcast signal is passed through limiter 1, the carrier components 22 and 31 are emphasized and the sideband components 23 and 24 (33, 34) are suppressed as follows. Depends on the reason.

In other words, since the AM broadcast signal is a carrier signal that is AM-modulated according to the audio signal, the limiter 1
This is because if the amplitude of the AM broadcast signal is limited, that is, if the AM component of the AM broadcast signal is suppressed, the remaining signal will be a signal in which the sideband signal is attenuated and the carrier component is emphasized.

Therefore, by applying the present invention, it is possible to selectively and stably detect only the required carrier signals without impairing the response speed.

Furthermore, since the narrowband filter 2 does not need to have such a steep frequency selection characteristic, it can be constructed at low cost.

[Brief explanation of the drawing]

FIG. 1 is an example of a system diagram of a detection circuit showing an embodiment of the present invention. Figure 2a shows the frequency energy distribution of the input signal when there is no broadcast wave on the receiving channel and there is a broadcast wave on the adjacent channel, and Figure 2a shows the frequency energy distribution of the input signal after it passes through limiter 1. It is. Figure 3a shows the frequency energy distribution when there is a broadcast wave on the receiving channel and there is no broadcast wave on the adjacent channel. be. 1...Limiter, 2...Narrowband wave detector, 3...Detector, 4...DC amplifier,
5...Input terminal, 6...Output terminal, 2
1.31...Carrier component of received channel signal, 22...Carrier component of adjacent channel signal, 23, 23', 24, 24', 33°33', 34
, 34'... Sideband wave.

Claims (1)

[Scope of utility model registration request] An AM system characterized by supplying an AM broadcast reception signal to an amplitude limiting circuit, emphasizing a carrier signal component and attenuating a sideband signal component, and detecting the carrier signal component to control an automatic channel selection operation. Broadcast receiver.