JPH07221663A - Super heterodyne reception system - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a super-heterodyne reception system that can eliminate spurious beats regardless of the order of harmonics. [Configuration] A frequency boundary region avoiding a spurious beat point where a difference between a harmonic of the first local oscillation frequency f _{L1 and} a harmonic of the second local oscillation frequency f _L2 matches the first intermediate frequency f _i1 for each reception frequency The second local oscillation frequency f _{L2 is set} to the second intermediate frequency f _i2 (9MH) depending on which of the frequency boundary regions the selected reception frequency f _R belongs to.
z) the first intermediate frequency f _i1 (70 MHz) below (61 MHz) or above
Switch to (79MHz). At that time, in order to prevent the spectrum inversion at the demodulation stage, the third local oscillation frequency f _{L3 is set} to the third frequency.
Only the intermediate frequency f _i3 (455 KHz) above the second intermediate frequency (9 MHz)
Switch to (9.455KHz) or down (8.545KHz).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superheterodyne reception system, and more particularly to a spurious beat elimination system.

[0002]

2. Description of the Related Art As is well known, in a superheterodyne receiving system, a plurality of local oscillators (which are usually composed of frequency synthesizers) are present in a frequency conversion stage. There is a phenomenon that the higher harmonics interfere with each other to derive a frequency that coincides with the reception frequency or the intermediate frequency, and as a result, a reception output is generated even though there is no reception input.

This phenomenon is called a spurious beat, and the smaller the number of points at which the spurious beat occurs and the value obtained by converting the spurious beat into the receiver input in the entire receiving frequency band of the receiving device, the better the receiving device. As described above, the spurious beat is one of the evaluation criteria of the receiving device.

The level of this spurious beat can be lowered to some extent if the local oscillator and the like are sufficiently shielded, but it cannot be sufficiently reduced. Therefore, conventionally, the following measures have been taken.

For example, as shown in FIG. 5, a portion of the frequency conversion stage of a superheterodyne receiver having three frequency conversion stages has an antenna 1 in a first mixer 2 as shown in FIG.
The reception frequency f _R at the first local oscillator 21
The second local oscillation generated by the second local oscillator 22 is converted into the first intermediate frequency f _i1 by the local oscillation frequency f _L1, and is converted by the second mixer 4 through the first intermediate frequency filter 3 having a pass bandwidth of B ₁ . The second intermediate frequency f _{depending on the} frequency f _L2
It is configured to convert to _{i2 and} to convert it into the third intermediate frequency f _i3 by the third local oscillation frequency f _L3 in the third mixer 6 via the second intermediate frequency filter 5 having the pass band width B ₂ . .

The received signal of the third intermediate frequency f _i3 is
After that, it is amplified to an appropriate level by an intermediate frequency amplifier, enters a demodulation stage, and is multiplied by a local oscillation frequency emitted by the local oscillator in a product detector to obtain a demodulated baseband signal.

In such a frequency conversion stage, basically, the first local oscillation frequency f _L1 is generally the reception frequency f _R
Since it is set higher than the above, in the first mixer 2, f _L1 −
f _R = f _i1 becomes frequency-converted by the related first intermediate frequency f _i1
Is output. Similarly, in the second mixer 4, when the second local oscillation frequency f _L2 is set lower than the first intermediate frequency f _i1, the second intermediate frequency f is converted by the relationship of f _i1 −f _L2 = f _{i2. Although i2} is output, the following measures have been taken as measures against spurious beats.

Namely, the pass band width B ₂ of the pass band width B ₁ of the first intermediate frequency filter 3 second intermediate frequency filter 5
The first local oscillation frequency f _L1 and the second local oscillation frequency f _L2 are each changed by the frequency Δf in the vicinity of the reception frequency at which the spurious beat is generated. The frequency Δf is a frequency having a value smaller than ½ of the pass band width B ₁ of the first intermediate frequency filter 3.

Specifically, if the spurious beat is caused by the sum or difference of the harmonics of the first local oscillation frequency f _L1 and the second local oscillation frequency f _L2 being equal to the first intermediate frequency f _i1 , The relationship between these three parties is the same as any integer N
It is shown by Numerical formula 1.

[0010]

[Equation 1]

Then, if the first local oscillation frequency f _L1 and the second local oscillation frequency f _L2 are respectively shifted by Δf, Equations 1 and 2 are obtained.

[0012]

[Equation 2]

[0013] Therefore, the _{Δf, (B 2/2)} <Δf <
(B _1/2) to select the following condition, the integer N and the M (N ±
If the condition M)> 1 is selected, the interference that occurs when the first local oscillation frequency f _L1 and the second local oscillation frequency f _L2 are each shifted by Δf is outside the pass band of the second intermediate frequency filter 5. It does not appear in the input stage of the third mixer 6 and no spurious beat occurs. Although not shown, the third local oscillator is a constant frequency oscillator. Therefore, according to this method, most of the spurious beats caused by the interference of higher harmonics can be removed.

[0014]

As described above, in the prior art, the frequencies of the two local oscillators that cause interference are each shifted by a minute frequency .DELTA.f, and most of the spurious beats caused by the interference of higher harmonics can be eliminated. However, as can be understood from the equation (2), the conventional removal method has a problem in that N = M, that is, interference due to harmonics of the same order has no effect and cannot be removed.

Even in the single super-heterodyne reception system, when the SSB (Single Side Band) signal is demodulated by product detection, it is so remarkable between the local oscillator of the frequency conversion stage and the local oscillator of the product detector of the demodulation stage. However, since similar spurious beats are generated, there is a demand for a unified solution.

An object of the present invention is to provide a super-heterodyne receiving system capable of eliminating spurious beats due to interference of harmonics of any order.

[0017]

In order to achieve the above object, the superheterodyne receiving system of the present invention has the following configuration. That is, in the super-heterodyne receiving system of the present invention, the sum or difference of the harmonics of the oscillation frequencies of the two local oscillators arranged one after another in the reception signal path is the signal of the two local oscillators. Means for storing frequency boundary region information that avoids spurious beat points that match the first frequency that is frequency-converted with the oscillation frequency of the local oscillator on the input side; and which of the frequency boundary regions the selected reception frequency belongs to Means to judge;
Means for switching the oscillation frequency of the local oscillator on the signal output side of the two local oscillators to the upper or lower side of the first frequency by a second frequency that is frequency-converted by the oscillation frequency of the local oscillator according to the determination; It is characterized by having.

[0018]

Next, the operation of the superheterodyne receiving system of the present invention configured as described above will be described. In the present invention,
Pay attention to the point that the spurious beat point caused by the interference of the harmonics generated by each of the two local oscillators arranged before and after in the reception signal path differs depending on the reception frequency, and the reception operation is performed in advance for each reception frequency. A region is set, and the oscillation frequency of the local oscillator on the signal output side is frequency converted by the oscillation frequency of the local oscillator on the signal input side according to the reception operation region. Switch the frequency above or below.

Therefore, since the receiving operation is carried out in a manner avoiding the point where the spurious beat is generated at each receiving frequency, in any super hederodyne receiving apparatus including the single super which performs the demodulating operation by the product detection, Spurious beats can be eliminated well regardless of the order of the harmonics. It should be noted that the inversion of the spectrum occurs due to the switching of the local oscillation frequency, but this can be solved by interlocking and changing the oscillation frequency of the appropriate local oscillator in the subsequent stage.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a frequency conversion stage of a receiving device to which a super-heterodyne receiving system according to an embodiment of the present invention is applied. In this super-heterodyne receiver, the frequency conversion stage is composed of three stages as in FIG. 5, and includes a first local oscillator 8, a second local oscillator 9 and a third local oscillator 10 which are frequency synthesizers. Microprocessor 1
1, a memory 12, and a frequency indicator 13 are basically provided.

The microprocessor 11 includes a tuning knob 14
The reception frequency designated by the operation is calculated, the frequency is displayed on the frequency display 13, and the frequency control data corresponding to the reception frequency is supplied to the first local oscillator 8, the second local oscillator 9, and the third local oscillator 10. However, in the present invention, the oscillation frequencies of the second local oscillator 9 and the third local oscillator 10 are referred to by referring to the memory 12 that stores frequency boundary data described later. Switching control.

The switching of the oscillation frequency (second oscillation frequency f _L2 ) of the second local oscillator 9 is performed by the harmonic of the second local oscillation frequency f _{L2 and} the harmonic of the first local oscillation frequency f _L1 emitted by the first local oscillator 8. The second local oscillation frequency f _{L2 is set} to the second intermediate frequency so that the sum or difference of the frequencies with the wave (“difference” is taken in this embodiment) does not match the first local oscillation frequency f _L1 . This is performed by switching the first local oscillation frequency f _L1 above or below by the amount of f _i2 .

The oscillation frequency of the third local oscillator 10 (third local oscillation frequency f _L3 ) is switched by switching the second local oscillation frequency f _L2 in order to prevent spectrum inversion at the demodulation stage. By interlocking with the switching of the frequency f _L2 , the third local oscillation frequency f _L3 emitted by the third local oscillator 10 is switched above or below the second local oscillation frequency f _L2 by the amount of the third intermediate frequency f _i3. Be seen.

For example, as shown in FIG. 2, the reception frequency f
_R is in the range of 1 MHz to 30 MHz, the first intermediate frequency f _i1 is 70 MHz, the second intermediate frequency f _i2 is 9 MHz,
If the third intermediate frequency f _i3 is 455 KHz, the first
The local oscillation frequency f _L1 is, as described above, f _L1 = f _R + f
_{Since i1} is the same as the conventional one in that the frequency is 71 MHz to 100 MHz, the second local oscillation frequency f _L2 and the third local oscillation frequency f _L3 are switched as follows.

That is, the second local oscillation frequency f _L2 is f _L2 = f
_i1 ± f _i2 , that is, f _L2a = 61 MHz and f _L2b = 79 MHz
And the third local oscillation frequency f _L3 is f
_L3 = f _i2 ± f _i3 , that is, f _L3a = 9.455 MHz and f
It is switched to _L3b = 8.545 MHz.

The basis of the above measures will be described with reference to the spurious chart shown in FIG. In FIG. 3, the horizontal axis represents the reception frequency f _R , and the vertical axis represents the frequency near the first intermediate frequency f _i1 among the mutual interference frequencies of the first and second local oscillators. The slanted straight lines in the figure indicate the frequency of mutual interference, and the intersection of these straight lines and the straight line of the first intermediate frequency f _i1 is the point where spurious beats occur.

Spurious beats are generated at an extremely large number of points even when considering the higher harmonics of the local oscillation frequency. However, the degree of interference is large, as shown in the figure, to lower harmonics up to the fifth order. This is due to the interference between the waves.

Now, the second local oscillation frequency f _L2 is f
Assuming that _L2a = 61 MHz is selected, the point at which the spurious beat of the second harmonic of the first local oscillation frequency f _L1 and the second local oscillation frequency f _L2 occurs can be obtained as follows. That is, when f _L1 = f _R + f _i1 is substituted into the relational expression of 2 (f _L1 −f _L2a ) = f _i1 , the reception frequency f _R
Is f _R = f _L2a − (½) _{fi 1} . Therefore, f
_{Since i1} = 70 MHz and f _L2a = 61 MHz, f _R = 26
MMHz is obtained, and a spurious beat occurs at the point where the reception frequency f _R is 26 MHz. In Figure 3, point P2
It is indicated by.

Similarly, the point of the spurious beat due to the third harmonic is f _R = f _L2a − (2/3) f _i1 = 1
This is 4.333 MHz, which is point P3 in FIG.
Similarly, fourth-order and fifth-order spurious beats occur at points P4 and P5, respectively.

If the second local oscillation frequency f _L2 is switched to f _L2b = 79 MHz in order to avoid these spurious beats, the spurious beats due to the second and third harmonics become the first intermediate frequency f _i1 . No match, but 4
Fig. 3 shows the spurious beats due to the next and fifth harmonics.
It occurs at the points indicated by 4 and Q5, respectively. The reception frequency f _{R at the} point Q4 is f _R = f _L2b − (3/4) f
to _i1, by substituting _{f L2b = 79MHz, f i1 =} 70MHz,
f _R = 26.5 MHz. The reception frequency f _{R at the} point Q5 is f _R = 23 MHz.

Therefore, an arbitrary frequency A between the points P3 and Q5 and an arbitrary frequency B between the points Q5 and P2.
, An arbitrary frequency C between the same P2 and the same Q4, and an arbitrary frequency D slightly higher than the frequency of the same Q4, and
As the local oscillation frequency f _L2 , the selected reception frequency f _R
Is f _{R ≤A} , f _L2b is set to A <f _R ≤B
The f _L2a if a region, B <f _R ≦ C becomes the f _L2b if region, C <f _R ≦ D made if area f _L2a
If f _L2b is automatically selected in the area where f _R > D, spurious beats can be generated even if there is interference between harmonics of the output of the first local oscillator 8 and the output of the second local oscillator 9. It can be appreciated that the receiver can be configured so that it does not occur.

The points (P2, P3, P4, P5, Q4, Q5) at which spurious beats shown in FIG. 3 are generated beforehand if the reception frequency range, the first intermediate frequency f _i1 and the second intermediate frequency f _i2 are determined. It is a value that can be calculated, and therefore
The frequency wave number boundary points of A, B, C, and D can also be set in advance.

That is, the frequency information of such a frequency boundary region is preset in the memory 12, and the microprocessor 11 performs the second receiving operation at the receiving frequency f _R designated by the tuning knob 14. When setting and controlling the oscillation frequency of the local oscillator 9, the selected reception frequency f _R
Is used to access the memory 12 to determine which region the reception frequency f _R belongs to from the magnitude relation with the frequency information of the frequency boundary region, and based on this, the oscillation frequency of the second local oscillator 9 as described above. To set. Then, each time the reception frequency f _R is changed, the same operation is performed and the oscillation frequency of the second local oscillator 9 is switched and set.

When the signal to be received is an SSB signal, the spectrum is inverted by controlling the switching of the second local oscillator 9, that is, in the case of USB (Upper Side Band) reception, it is demodulated in the state of being inverted to LSB. To be done. In order to prevent this, in the present embodiment, the switching control of the third local oscillator 10 is also interlocked with the switching control of the second local oscillator 9.

[0035] Specifically, the third local oscillation frequency f _L3 is the second local oscillation frequency, the f _L3a (9.455MHz) when the _{f L2 = f L2a (61MHz)} , f L2 = f L2b (79MHz )
In that case, the setting is changed to f _L3b (8.545 MHz). As a result, for example, as shown in the upper part of FIG. 2, it is possible to correct the inversion of the spectrum in the frequency conversion stage and give the demodulation stage a received signal having a regular spectrum.

FIG. 1 shows the case where the number of frequency conversion stages is three, but the correction of the spectrum inversion in the case of four or more stages is performed by setting at least one oscillation frequency of the local oscillators from the third stage to the final conversion stage to the first frequency. The switching control is performed in conjunction with the switching control of the two local oscillators 9.

As is apparent from the above description, the correction of the spectrum inversion can be performed by changing the local oscillation frequency of the product detector at the demodulation stage.
Especially in the case of a double superheterodyne receiver,
It will be performed in the demodulation stage.

Further, as described above, even in the single super heterodyne reception system, SSB (Single Side Ban
In some cases, the signal of d) is demodulated by product detection. In this case, the oscillation frequency of the local oscillator of the product detector at the demodulation stage is the frequency of the product detection frequency based on the same idea as described above. Switching above or below the intermediate frequency generated in the conversion stage.

Specifically, for example, FIG. 4 shows a case of receiving a USB, but the oscillation frequency f of the local oscillator of the product detector 17 is smaller than the intermediate frequency f _{i of the} oscillation frequency f _L of the mixer 16. case, f = f _i -1.5K
Set in Hz, in the case of _{f L> f i, f =} f i + 1.5K
Set it to Hz. Note that 1.5 KHz is the frequency of the detection signal.

[0040]

As described above, in the super-heterodyne receiving system of the present invention, spurious beats caused by interference of higher harmonics generated by two local oscillators arranged one after another in the received signal path. Focusing on the points that differ depending on the reception frequency, set the reception operation area in advance for each reception frequency, according to the reception operation area,
Since the oscillation frequency of the local oscillator on the signal output side is switched above or below the frequency converted by the oscillation frequency of the local oscillator on the signal input side by the frequency converted by the oscillation frequency of the local oscillator, In spite of the fact that spurious beats are avoided while avoiding points that cause spurious beats, spurious beats are sufficiently independent of harmonic orders in any super-heterodyne receiver including single super that performs demodulation with product detection. There is an effect that can be eliminated. It should be noted that the spectrum inversion occurs due to the switching of the local oscillation frequency, but this is because the oscillation frequency of the appropriate local oscillator in the subsequent stage is changed in conjunction, so that the spectrum inversion at the demodulation stage can be prevented. There is also.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of a receiving device to which a super-heterodyne receiving system according to an embodiment of the present invention is applied.

FIG. 2 is a system diagram illustrating an oscillation frequency switching operation and a spectrum.

FIG. 3 is a spurious chart for explaining a relationship between a point where a spurious beat is generated, a reception frequency, and an oscillation frequency switching region.

FIG. 4 is a system diagram showing an application example to a single super-heterodyne reception system.

FIG. 5 is an explanatory diagram of a conventional super heterodyne reception system.

[Explanation of symbols]

 1 Antenna 2 1st mixer 3 1st intermediate frequency filter 4 2nd mixer 5 2nd intermediate frequency filter 6 3rd mixer 7 3rd intermediate frequency filter 8 1st local oscillator 9 2nd local oscillator 10 3rd local oscillator 11 Microprocessor 12 memory 13 frequency display 14 tuning knob 16 mixer 17 product detector 18 AF Amp (audio amplifier)

Claims (6)

[Claims] 1. A pair of two are arranged one after another in a received signal path.
A spurious beat point at which the sum or difference of the harmonics of the oscillation frequencies of the respective local oscillators matches the first frequency that is frequency-converted by the oscillation frequency of the local oscillator on the signal input side of the two local oscillators. Means for storing the avoided frequency boundary area information; means for determining which of the frequency boundary areas the selected reception frequency belongs to;
Means for switching the oscillation frequency of the local oscillator on the signal output side of the two local oscillators to the upper or lower side of the first frequency by a second frequency that is frequency-converted by the oscillation frequency of the local oscillator according to the determination; A super-heterodyne receiving system characterized by having. 2. The superheterodyne reception system according to claim 1, wherein when the two local oscillators are in the frequency conversion stage, the local oscillator on the signal input side is the first local oscillator.
A local oscillator, the local oscillator on the signal output side is a second local oscillator, the first frequency is a first intermediate frequency, and the second frequency is a second intermediate frequency; . 3. The super-heterodyne reception system according to claim 2, wherein when the frequency conversion stage has two stages, the oscillation frequency of the local oscillator of the product detector of the demodulation stage is demodulated according to the switching. Means for switching so as not to invert the spectrum of the superheterodyne reception system. 4. The super-heterodyne receiving system according to claim 2, wherein when the frequency conversion stage is three or more, the oscillation frequency of at least one local oscillator among the local oscillators from the third stage to the final conversion stage is set. A super-heterodyne reception system characterized by comprising means for switching so that the spectrum of the demodulated baseband signal is not inverted. 5. The super-heterodyne reception system according to claim 2, wherein when the frequency conversion stage has three or more stages, the oscillation frequency of the local oscillator of the product detector of the demodulation stage is demodulated to the baseband in accordance with the switching. A super-heterodyne reception system characterized by comprising means for switching the spectrum of the signal so as not to be inverted. 6. The super-heterodyne reception system according to claim 1, wherein among the two local oscillators, the signal input side local oscillator is a frequency conversion stage local oscillator and the signal output side local oscillator is a demodulation stage. Is a local oscillator of the product detector, the first frequency is an intermediate frequency generated in the frequency conversion stage, and the second frequency is a detection frequency of the product detection;