JPS6233404Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in double superheterodyne receivers.

For example, in the case of a conventional multi-band superheterodyne receiver in the VHF band, a plurality of frequency conversion circuits each consisting of a mixing circuit and a local oscillation circuit are provided.
Usually, the output of each frequency conversion circuit is switched using a band switching switch. In that case, the multi-band receiver may be one with only a single superheterodyne frequency conversion circuit or one with a mixture of single and double superheterodyne frequency conversion circuits.

By the way, when a local oscillation circuit is provided for each frequency conversion circuit for each band in this way, the number of local oscillation circuits increases and the configuration becomes complicated.
The number of parts in the receiver increases, and it takes time to assemble and adjust, which ultimately leads to an increase in the price of the receiver.

In view of these points, the present invention aims to provide a double superheterodyne receiver that has a simple circuit configuration, is easy to assemble and adjust, and is capable of stabilizing the high frequency circuit system.

A pair of first mixing circuits, one of which is upper heterodyne and the other is lower heterodyne, one first local oscillation circuit provided in common to the pair of first mixing circuits, and a pair of first mixing circuits. a band switching switch that switches between a pair of first intermediate frequency signals; a second mixing circuit that is supplied with the pair of first intermediate frequency signals from the band switching switch and outputs a common second intermediate frequency signal; and one second local oscillation circuit provided corresponding to the two mixing circuits, the first local oscillation circuit generates a local oscillation signal in a common frequency range for the pair of bands, and the second local oscillation circuit generates a local oscillation signal in a common frequency range for the pair of bands. The circuit is configured to generate a pair of local oscillation signals corresponding to the pair of first intermediate frequency signals.

Hereinafter, an embodiment of the present invention will be described in detail with reference to FIG. This double superheterodyne receiver shown in Figure 1 is a 2-band FM receiver in the VHF band.
This is a radio receiving board that can receive broadcast radio waves. still,
Although not shown in FIG. 1, this radio receiver also has an AM radio receiving section. However, since this is irrelevant to the present invention, its explanation will be omitted here.

Figure 2 shows the dial scale plate of this radio receiver, where the first band includes FM audio broadcasts and FM radio broadcasts of the low channel of television broadcasting, and the second band includes FM radio broadcasts. Includes weather (weather forecast) radio broadcasts and FM audio broadcasts of the Haiti channel of Television Broadcasting. Although the third band AM radio broadcast is not relevant in the embodiment shown in FIG. 1, it is shown on the dial scale plate.

In FIG. 1, 1 is a receiving antenna common to the first and second bands. 2a and 2b are high frequency circuits for the first and second bands, respectively, and are connected to the antenna 1. Note that these high frequency circuits 2a and 2b can also be omitted. These high frequency circuits 2a,
2b, the first stage for the first and second bands is
Frequency conversion circuits 3a and 3b are connected. 4
a and 4b are first mixing circuits of frequency conversion circuits 3a and 3b. Reference numeral 5 designates one first local oscillation circuit provided in common to these mixing circuits 4a and 4b. 6a and 6b are tuning circuits connected to the next stage of the mixing circuits 4a and 4b. Tuning circuits 6a, 6b
The output of is selectively switched by a band changeover switch 7.

Here, in the first band frequency conversion circuit 3a, 55
The second band frequency conversion circuit 3b receives broadcast waves of 161 to 217 MHz. Also, in local oscillation circuit 5, 102.5~
Generates a 158.5MHz local oscillation signal. The oscillation frequency of this local oscillation circuit 5 is varied during tuning. In this case, the tuning frequency of the tuning circuit of the high frequency circuit 2a or 2b is varied at the same time. Tuning circuits 6a, 6b
are the frequencies from the outputs of the mixing circuits 4a and 4b, respectively.
This is for extracting intermediate frequency signals of ₁ and ₂ . Then, the reception frequency of the first band is F ₁ ,
The reception frequency of the second band is F ₂ , and the local oscillation circuit 5
If the local oscillation frequency of is F ₃ , then F ₁ and ₂ can be expressed as follows, for example.

F ₃ −F ₁ = ₁ = 47.5MHz F ₂ −F ₃ = ₂ = 58.4MHz Therefore, in the first frequency conversion circuits 3a and 3b, the former is an upper heterodyne and the latter is a lower heterodyne.

The reason why frequencies ₁ and ₂ of the intermediate frequency signals are made different here is to reduce the number of signals of unintended broadcasting stations that come in as image frequencies and to reduce interference. If the first intermediate frequency signal is the same frequency signal for the first and second bands, the first local oscillation signal will be 108 to 164 MHz, and the first band (55 to 111 MHz) signal will be upper-heterodyned. If the selectivity of the high-frequency circuit is not sufficient when receiving at the same time, all frequencies in the second band (161 to 217 MHz) will be received as image frequencies, increasing interference during reception. , it becomes very difficult to receive the desired signal (or the reception condition deteriorates). Also, the second band (161~
Even when receiving a signal of 217 MHz) by lower heterodyne, the first band (55
~111MHz) are all received as image frequencies, resulting in severe interference.

On the other hand, when the first intermediate frequency signal is a signal with a different frequency for the first and second bands as in the present invention, when the first band (55 to 111MHz) is received by upper hederodyne. Since the first local oscillation signal changes in the range of 102.5 to 158.5MHz,
Even if the image frequency is 150-206MHz, which is 11MHz lower than the frequency range of the second band, and the selectivity of the high-frequency circuit is not very good, image interference from powerful broadcasting stations can be theoretically avoided.

Also, when receiving the second band (161~217MHz) by lower heterodyne, the first local oscillation signal
Since it changes in the range of 102.5 to 158.5 MHz, the image frequency is 44 to 100 MHz, which is also 11 MHz lower than the frequency range of the first band, making it possible to avoid nearly half of the image interference from strong FM broadcasting stations, eliminating interference. can be reduced.

The output of the band switching switch 7 is supplied to a first intermediate frequency amplification circuit 8 and amplified. A tuning circuit 9 is provided at the next stage of the first intermediate frequency amplification circuit 8. As mentioned above, the first frequency conversion circuit 3
Since the intermediate frequencies ₁ and ₂ of a and 3b are different, the tuning frequency of this tuning circuit 9 is also ₁ and _2.
The configuration is such that the band changeover switch 13 is used to change the band. That is, capacitor 1
0 and the coil 11 are connected between the output terminal of the amplifier 8 and the ground, and a capacitor 12 is connected between the output terminal of the amplifier 8 and the ground via the band switching switch 13. It is connected. When receiving the first band, the band selection switch 13 is turned on and the capacitor 12 is connected between the output terminal of the amplifier 8 and the ground, and when receiving the second band, the band selection switch 13 is turned on. 13 is turned off, and capacitor 12 is not connected.

The first intermediate frequency signal from the tuning circuit 9 is supplied to the second frequency conversion circuit 14. The second frequency conversion circuit 14 includes a second mixing circuit 15 and a second local oscillation circuit 16. In this case, since the frequencies of the first intermediate frequency signal from the tuning circuit 9 are ₁ and _f2 , the second local oscillation circuit 16
The local oscillation frequency is also varied between ₃ and ₄ . In this case, ₃ is 58.2MHz, ₄ is
It is 69.1MHz.

Reference numeral 17 denotes a resonant circuit of this local oscillation circuit 16, which is provided with a resonant circuit consisting of a capacitor 18 and a coil 19 like the tuned circuit 9, and a capacitor 20 is connected in parallel to this capacitor 18 via a band changeover switch 21. I try to do that.
Then, when receiving the first band, the capacitor 20 is connected to the capacitor 18, and when receiving the second band, the band changeover switch 21 is switched so that the capacitor 20 is not connected. The band switching switches 7, 13, and 21 are switched in conjunction with each other, and FIG. 1 shows the switching state when receiving the first band.

Then, the second local oscillation circuit 16 generates a second
The local oscillation signal is supplied to the second mixing circuit 15. Further, a tuning circuit 22 is connected to the next stage of the mixing circuit 15. This tuning circuit 22
This is for extracting a second intermediate frequency signal having a second intermediate frequency of ₀ from the output of the mixing circuit 15. This can be expressed as follows.

₃ - ₁ = _{0 4} - ₂ = ₀ In this case ₀ is 10.7MHz. In this case, the frequency ₀ of the second intermediate frequency signal is the first intermediate frequency ₁ , ₂ and the second local oscillation frequency ₃ , ₄ .
This is the frequency of the difference between the two, but of course it can also be the sum of the frequencies. The output of the tuning circuit 22 is supplied to a second intermediate frequency amplification circuit 23. Furthermore, the output of this amplification circuit 23 is sent to a detection circuit, in this example, an FM demodulation circuit 2.
4 and is demodulated (in the case of stereo broadcasting, the demodulated output is stereo demodulated, but this is omitted in this case), and the demodulated output is amplified by the low frequency amplification circuit 25. After that, speaker 26
supplied to Moreover, the second intermediate frequency amplification circuit 23
The output is supplied to the second local oscillation circuit 16 as an AFC signal via a capacitor 27.

According to the present invention described above, one first local section provided in common for a pair of first mixing circuits, one of which is an upper heterodyne and the other is a lower heterodyne, which are provided corresponding to a pair of bands. Since an oscillation circuit is provided, the circuit configuration is simple, adjustment is easy, and the high frequency system is stabilized. (Since the first local oscillation circuit is not switched for each band, it is easy to stray due to switching, and there is no possibility of abnormal oscillation due to stray inductance. Therefore, it is possible to obtain a double superheterodyne receiver that can ensure reception of each band without any fear. In this way, for a pair of first mixing circuits corresponding to a pair of bands, a common one
If two local oscillation circuits are provided, image interference between the received signals of each band becomes a problem. Therefore, in the present invention, the frequency range of the first local oscillation signal is common to each band, and the frequency range of the first local oscillation signal is common to each band, and Since a plurality of first intermediate frequency signals of different frequencies are obtained, image interference between received signals of each band is reduced. Furthermore, since the configuration is simple, the price is low. Furthermore, when the dial scales for each band are attached to a common scale plate as shown in FIG. 2, the local oscillation circuit is common, which facilitates the design.

Furthermore, when adopting the configuration shown in the above embodiment, not only the first local oscillation circuit of the first frequency conversion circuits is common, but also the active elements of the second frequency conversion circuits are at least common.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a pattern diagram showing a dial scale plate. 3a and 3b are first frequency conversion circuits for each band;
4a and 4b are first mixing circuits for each band; 5 is a first local oscillation circuit common to each band; 7 is a band selection switch; 8 is a first intermediate frequency amplification circuit; 9
13 is a tuning circuit, 13 is a band switching switch, 14 is a second frequency conversion circuit, 15 is a second mixing circuit, 16
1 is a second local oscillation circuit, and 17 is a resonant circuit.

Claims (1)

[Scope of utility model registration request] A pair of first mixing circuits, one of which is upper heterodyne and the other is lower heterodyne, one first local oscillation circuit provided in common to the pair of first mixing circuits, and the pair of first mixing circuits. a band switching switch that switches between a pair of first intermediate frequency signals, and a second mixing circuit that is supplied with the pair of first intermediate frequency signals from the band switching switch and outputs a common second intermediate frequency signal. and the second
one second local oscillation circuit provided corresponding to the mixing circuit; the first local oscillation circuit generates a local oscillation signal in a common frequency range for the pair of bands; The oscillation circuit is the first of the pair.
A double superheterodyne receiver configured to generate a pair of local oscillation signals corresponding to an intermediate frequency signal.