JPH02202215A - Radio receiver - Google Patents

Abstract

PURPOSE:To attain an automatic channel selection for a broadcast of a desired frequency only by connecting a high pass filter and a bypass circuit switchingly to an antenna and a high frequency amplifier section when an oscillated frequency reaches a prescribed threshold level. CONSTITUTION:A double-throw transfer switch 1 being a switching means is interposed between an antenna 51 and a high frequency amplifier 52. Then a high pass filter 2 is interposed between terminals 1a and 1b and terminals 1c, 1d are bypassed by a bypass circuit 3. A main control section 4 receives high frequency information outputted from an oscillation circuit 5-4a to activate the transfer switch 1 when a seek frequency fd reaches 900kHz. Thus, the arrived radio wave whose frequency band is less than 810kHz is nearly completely cut off at the channel selection of the frequency of the 2nd harmonic of the arrived radio wave.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a radio receiver, and particularly relates to an automatic channel selection (S
EEK) function.

[Conventional technology]

According to the AM broadcasting channel plan, there are 9 (k)
It is supposed to be broadcast at a frequency that is an integer multiple of Hz).

Therefore, when you press the SEEK button, the local oscillation frequency increases or decreases every 9 (kHz).
Many radio receivers have been proposed in the past that have an automatic tuning function that automatically stops at that station (frequency) if there is an incoming radio wave of a certain strength or higher.

A conventional example of this type of radio receiver is shown in FIG. The conventional example shown in FIG. 3 is an antenna 5 for receiving AM radio broadcasting.
1, a high frequency amplifying section 52 that amplifies the radio waves received by this antenna 51, a mixing section 53 that is attached to the output stage of this high frequency amplifying section 52 and converts the amplified high frequency into an intermediate frequency, and this mixing section 53 and a local oscillation section 54 that outputs a high frequency.

Furthermore, an intermediate frequency amplification circuit 56 that amplifies the intermediate frequency output from the mixing section 53 is provided at the output stage of the mixing section 53 . This intermediate frequency amplification circuit 56 cuts (attenuates) frequencies other than the frequency band around the amplifier 56a and a preset intermediate frequency f, [k7] (usually set to 450 (k7)). Further, an AM detection circuit 57 is provided at the output stage of the intermediate frequency amplification circuit 56.

Then, the intermediate frequency amplification circuit 56 is outputted from the mixing section 53.
A main control section 55 is provided that performs control to vary and stop the oscillation frequency f of the local oscillation section 54 according to the signal level of the intermediate frequency amplified by the main control section 55.

To explain this in more detail, the mixing section 53 includes the high frequency amplifying section 5
Frequency fdO high frequency output from 2 and local oscillation section 54
It has a function of outputting an intermediate frequency of frequency r- (=rtrd) by mixing the high frequency of frequency r1 outputted from .

The local oscillation section 54 has an oscillation circuit 54a and a main control section 55 that controls the frequency of the high frequency output from the oscillation circuit 54a.
The frequency variable setting circuit 54b is configured to set according to the command of the frequency variable setting circuit 54b.

The main control unit 55 is actually composed of a microcomputer, etc., and receives commands from the outside via a seek button (not shown).
The variable frequency setting circuit 54b is controlled to variably set the oscillation frequency f to increase or decrease every 9 (kHz), and the signal level of the intermediate frequency output from the bandpass filter 56b described above exceeds a predetermined level. In other words, if there is an incoming radio wave, a command is issued to the frequency variable setting circuit 54b to stop the frequency variable operation at that point. . Here, the frequency f of the intermediate frequency output from the mixing section 53 is always a constant value. Therefore, as the oscillation frequency ft changes, f
, =f, -f, incoming radio waves with frequencies that satisfy the relationships are selected at any time.

[Problem to be solved by the invention]

AM waves are modulated by changing the amplitude of the carrier wave according to the waveform of the audio current, so when the strength of the radio wave increases, the carrier frequency (the frequency of the carrier wave, in AM broadcasting, 522 to 1629 (k) 1z) ) is distorted and harmonics (second harmonics) are generated.

Therefore, in the above conventional example, for example, FEN(i
If you press the seek button in a place where strong radio waves of 810 (kHz), which corresponds to 810 (kHz), are received, the 810 (kHz)
), there was also the problem that the seek operation automatically stopped at 1620 (kHz).

[Purpose of the invention]

An object of the present invention is to improve the disadvantages of the conventional example, and when a strong input is applied, the desired signal is distorted (1629 (1629)).
An object of the present invention is to provide a radio receiver that can effectively prevent a seek operation from stopping at that frequency even if there is a harmonic within that frequency.

(Means for Solving the Problems) The present invention includes an antenna for receiving AM radio broadcasting, a high frequency amplifying section that amplifies radio waves received by the antenna,
It includes a mixing section that is attached to the output stage of the high frequency amplification section and converts the amplified high frequency into an intermediate frequency, and a local oscillation section that outputs the high frequency to the mixing section. It is also equipped with a main control section that controls the variation and stop of the oscillation frequency of the local oscillation section according to the signal level of the intermediate frequency output from the mixing section. Furthermore, between the antenna and the high frequency amplification section,
A high-pass filter and a bypass circuit are provided in parallel, and a switching means is provided for these high-pass filters and bypass circuits. The main control section is configured to have a switching function for activating the switching means when the oscillation frequency reaches a predetermined threshold value. This aims to achieve the above-mentioned objective.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

Here, the same reference numerals will be used for the same components as in the conventional example described above, and the explanation will be simplified or omitted.

In the embodiment shown in FIG. 1, a transfer switch 1 with two circuits as a switching means is interposed between an antenna 51 and a high frequency amplification section 52. A high-pass filter (bypass filter) 2 is interposed between the terminals 1a and 1b shown in FIG. 1, and a bypass circuit 3 is provided between the terminals 1cm1d. Here, as the high-pass filter 2, one having a cutoff frequency fc=950 (kHz) and having the characteristics shown in FIG. 2 is used.

Further, in this embodiment, a main control section 4 is provided in place of the main control section 55 in the conventional example described above. The main control section 4 is composed of a microcomputer, etc., like the main control section 55, and has the same functions.

Furthermore, the main control unit 4 receives the high-frequency frequency information output from the oscillation circuit 5-4a as feedback, and adjusts the oscillation frequency f to 1350 (k7), that is, the seek frequency f4 to 900 (kHz). (In this embodiment, the intermediate frequency f is set to 450 (k7)).

To explain this in more detail, the main control unit 4 controls the seek frequency f
, is in the range of 522 to 900 (k7), that is, the oscillation frequency ft
is in the range of 972 to 1350 (kHz), the solenoid section IA of the transfer switch 1 is set to the operating state via the power supply circuit 50 based on the feedback information from the transmitting circuit 54a, and the transfer switch 1 is connected to the bypass circuit 3 side. do. On the other hand, in this main control section 4, the seek frequency fa is 900 to 1629 [kHz] (
7) The range, that is, the oscillation frequency f, is 1350 to 2079 (
kHz), a command is issued to the power supply circuit 50 to stop the power supply to the solenoid part IA of the transfer switch 1, and the solenoid part IA is put into a non-operating state. Therefore, the transfer switch 1 is connected to the high-pass filter 2 side by a means for returning to its original position (not shown).

The other configurations are the same as the conventional example described above.

Next, the operation of the above embodiment at the time of seek (at the time of automatic channel selection) will be explained.

Now, if the desired broadcast frequency is 531 [kHz],
The doubled frequency is 1062 (kHz).

Initially, the set frequency (seek frequency) of the radio receiver
Suppose that the frequency is set to 522 (kHz). In this state, it is assumed that a seek button (not shown) on the ``rUP'' side is pressed.

(At this time, the transfer switch 1 is connected to the bypass circuit 3 side as described above.) A seek operation is started, and the display frequency of the radio receiver increases, and the
The seek operation stops when the frequency matches 31 (kHz).

Next, from this state, if you press the seek button on the rUP (up) side again, the frequency will gradually increase to 900 (k).
Hz), the transfer switch 1 is switched to the high-pass filter 2 side by the function of the main control section 4.

In this case, 1062 (k ce) (2X531 (k 7))
Even if the frequency reaches 531 (kHz), the high-pass filter 2
Since the incoming radio wave z) has been cut (attenuated), the incoming radio wave signal is not input to the high frequency amplification circuit 52 at the subsequent stage. Therefore, the frequency of the second harmonic of the incoming radio wave is 1
At 062 (kHz), the seek operation does not stop and the frequency continues to increase.

As described above, according to this embodiment, the oscillation frequency f is 13
50 (kHz), that is, the seek frequency f.

When the frequency exceeds 900 (kHz), the transfer switch 1 is switched to the high-pass filter 2 side, so that the 81
Incoming radio waves in the frequency band below 0 (kHz) can be almost completely cut when tuning the frequency band of the second harmonic of the incoming radio wave, so the seek operation stops when the frequency of the second harmonic is reached, unlike in the conventional case. There is an advantage that this inconvenience can be effectively avoided.

(Effects of the Invention) Since the present invention is configured and functions as described above, according to the present invention, when the oscillation frequency reaches a predetermined threshold, the main control section connects the high-pass filter and the bypass circuit to the antenna. For example, as in the above embodiment, the intermediate frequency f. is set to 450 [k7] as usual, and the threshold value is set to 1350 (k7).
By setting the oscillation frequency f to 135
When it exceeds 0(k & ), that is, the seek frequency r, (=
When f, -f, ) exceeds 900 (kHz), the antenna is connected to the high frequency amplification section via a high-pass filter, so that the incoming radio waves in the frequency band below 810 (kHz) are When selecting the second harmonic frequency band, it can be almost completely cut out. Therefore, when a strong input is applied, even if the desired signal is distorted and the second harmonic is within 1629 (kHz), the second harmonic will be cut off almost completely. It is possible to provide an unprecedented and excellent radio receiver that can effectively prevent a seek operation from stopping at a certain frequency and can automatically tune only broadcasts of a desired frequency.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, FIG. 2 is an explanatory diagram showing the characteristics of the high-pass filter shown in FIG. 1, and FIG.
The figure is a block diagram showing the configuration of a conventional example. DESCRIPTION OF SYMBOLS 1...Transfer switch as a switching means, 2...High-pass filter, 3...Bypass circuit, 4...Main control section, 51...・・・
・Antenna, 52... High frequency amplification section, 53...
...Mixing section, 54...Local oscillation section.

Claims (1)

[Claims] (1) An antenna for receiving AM radio broadcasting, a high-frequency amplification section that amplifies the radio waves received by this antenna, and a high-frequency amplification section that is attached to the output stage of this high-frequency amplification section and that converts the amplified high frequency into an intermediate frequency. A main control unit that includes a mixing section and a local oscillation section that outputs a high frequency to the mixing section, and controls the oscillation frequency of the local oscillation section to vary and stop depending on the signal level of the intermediate frequency output from the mixing section. In a radio receiver equipped with a high-frequency amplifier, a high-pass filter and a bypass circuit are interposed in parallel between the antenna and the high-frequency amplification section, and a switching means is provided for these high-pass filters and the bypass circuit, so that the main A radio receiver characterized in that the control section has a switching function for activating the switching means when the oscillation frequency reaches a predetermined threshold value.