JPS6014526A - All-band double heterodyne am receiver - Google Patents

Abstract

PURPOSE:To obtain a good receiving characteristic with a simple circuit constitution by setting the first intermediate frequency on the outside of upper band of a receiving band and connecting a tuning circuit having a series resonance and a parallel resonance closely to the output, and setting the frequency of an image signal at a minimum output point of the series resonance point. CONSTITUTION:The transmission characteristic appearing across both ends of a capacitor 19 is an output characteristic shown in a figure, and a maximum output point due to the parallel resonance characteristic and a minimum output point due to the series resonance characteristic are obtained. In this case, values of a coil 16 and capacitors 17, 18, and 19 are so selected properly that the maximum output point has the first intermediate frequency and the minimum output point has the image frequency generated by the second local oscillating circuit. By this constitution, an ANT input circuit secures sufficient image characteristic, degree of amplification, and degree of selection even with an LPF, and further, the local oscillation can be covered with a single variable capacitor to make a band changeover switch unnecessary.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an all-band AM receiver that can obtain good reception characteristics with a simple configuration.

(Configuration of conventional example and its problems) Figure 1 shows 1! of the double superheterodyne system of a conventional all-band AM receiver. A schematic diagram is shown. A is 1,
2, 3, and 4.5. 1 is a mixing circuit that performs the first frequency conversion.

Reference numeral 2 denotes a first local oscillation circuit which is variable in frequency and oscillates at a receiving frequency and a first intermediate frequency. For this reason, it is difficult to perform all-wave reception (500 KIlz to 28 MH2) in a single band, so it is common to use multiple bands. 3 is an intermediate frequency amplification circuit which selectively amplifies an intermediate frequency from among the frequency conversion outputs of the mixing circuit 1; In general, the resonance characteristics of the tuned circuit are used, and the first intermediate frequency is a few Mllz higher than IN)Iz, and the image ratio is set high. 64 is a mixing circuit for the second frequency conversion. The difference between the local l@oscillation frequency and the first intermediate frequency of the two local oscillation circuits 5 becomes the second intermediate frequency, which is amplified by the second intermediate frequency amplifier 6 and detected by the detection circuit 7.

The second intermediate frequency is normally set at 450 KHz to provide amplification and selectivity. In this method, the first
When an intermediate frequency enters the reception band, there are points where reception is impossible, so the band is divided near the first intermediate frequency, and in the lower frequency band, a single super,
In high frequency bands, methods such as a double super system are used, and an ANT tuning circuit is required, which has the drawback that the switching circuit for this is extremely complicated.

(Object of the Invention) The present invention is particularly effective when an all-band AM receiver is configured with a single synthesizer, and is intended to obtain good reception characteristics with a simple circuit configuration.

(Structure of the Invention) The present invention relates to a first local oscillation circuit and a first intermediate frequency selection circuit that operate in the same manner as the circuit operation of block A of the double superheterodyne system shown in FIG. The intermediate frequency created by the oscillation circuit is set outside the upper band of the required reception band, and a tuned circuit having series resonance and parallel resonance in close proximity is connected to the output of the first frequency conversion, and the received signal is tuned to the parallel resonance point. is set to the maximum output, and the minimum output point of the series resonance point is configured to be the frequency of the image signal generated by the second local oscillation circuit.

(Description of Embodiment) FIG. 2 shows an embodiment of the present invention, which corresponds to block A in FIG. In this circuit configuration, 11 is an ANT input circuit, and generally a variable tuning circuit is used, but in the method of the present invention, a fixed low-pass filter can sufficiently exhibit practical effects. 1
A resistor 2.13 is a bias resistor of the 1-transistor 14 for mixing. ] 5 is a first local oscillation circuit whose frequency is variable, and is set so that the difference between the received signal and the local oscillation signal becomes the first intermediate frequency. 16 is a coil, 17.18.
19 is a capacitor that applies the output of the mixer to both ends of the coil 16. The transmission characteristics appearing at both ends of the capacitor 19 exhibit output characteristics as shown in FIG. 3, with a maximum output point due to the parallel resonance characteristic and a minimum output point due to the series resonance point. At this time, coil 16, capacitor 17°18,
19 is appropriately selected so that the maximum output point is the first intermediate frequency and the minimum output point is the image frequency generated by the second local oscillation circuit.

20 and 21 are bias resistors, 22 is a transistor, 2
3 is a load resistance. 1-Resistor 22 is an amplifier of the selected first intermediate frequency, and the output is connected to capacitor 2.
4 through the transistor 27 and the second local oscillator circuit 28
The second intermediate frequency mixed with and outputted is selectively outputted by the intermediate frequency transformer 29.

(Effects of the Invention) According to the double superheterodyne method according to the present invention having the above-described configuration, the effect of the first intermediate frequency amplification circuit makes it possible to easily obtain a sufficient image ratio even if a higher intermediate frequency is selected. It is a skill that can be realized with circuits. Therefore, it is possible to select the first intermediate frequency outside the AM all-wave reception frequency band. Therefore, sufficient image characteristics and amplification degree 1 selectivity can be ensured even by using an untuned low-pass filter without making the ANT input circuit a variable tuning type. In addition, the local oscillation frequency is changed to AM all-band reception (3
This can be realized by providing an oscillation circuit (0 to 60 MHz), and it is possible to sufficiently cover local oscillation with a single varicap.

Therefore, there is no need for a conventional switch for switching hands.

If applied to current digital synthesizer type local oscillation circuits, the frequency stability of the local oscillation circuit can be achieved with crystal precision, and AM all-band reception can be achieved with a simple ANT input circuit and a single local oscillation circuit. It becomes possible to ensure good image characteristics and selection characteristics.

Furthermore, in a digital synthesizer system using a microcomputer, the reception frequency can be extended to the 8W band by a simple change in software, resulting in a system that hardly requires a cyst amplifier for SW reception.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional double superheterodyne system, FIG. 2 is a diagram showing an embodiment of the present invention, and FIG. 3 is a diagram showing characteristic curves.゛, 11... ANT input circuit, 14... mixing transistor, 15...
First local oscillation circuit, 22... First intermediate frequency amplification transistor, 27... Mixing transistor, 28.
...Second local oscillation circuit. Patent applicant Matsushita Electric Industrial Co., Ltd.

Claims (1)

[Claims] The all-band AM receiver is configured with a double superheterodyne system, the first intermediate frequency is set outside the upper band of the desired reception band, and the first intermediate frequency amplification circuit is set as the maximum amplification point with the tuning frequency as the parallel resonance frequency. , is connected to the second mixing circuit so that the series resonance frequency is a frequency that is twice the second intermediate frequency from the parallel resonance frequency, and is connected to the second mixing circuit, and the local oscillation frequency of the second mixing circuit is set to this point. An all-band double superheterodyne AM receiver characterized by having a frequency intermediate between a parallel resonance frequency and a series resonance frequency.