JPS6312408B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a synthesizer receiver, and its purpose is to automatically switch the signal passband width in an intermediate frequency amplification stage or the like in order to change the selection characteristics for a desired signal. The objective is to provide a synthesizer receiver that can.

Generally, in signal reproduction by a receiver, the signal passing bandwidth (hereinafter referred to as bandwidth) is
The wider the detection signal, the higher the fidelity of the detected signal. However, on the other hand, in order to remove the influence of interfering signals near the desired station, the narrower the bandwidth, the better. In recent years, receivers (especially FM receivers) have been able to switch the bandwidth of their intermediate frequency amplification stage, so that when there is no nearby interference waves, it receives in a wide band, and when there is interference waves, it receives in a narrow band. It is in the direction of However, since this switching of the bandwidth is usually done manually, it is easy to judge when the presence of adjacent interference waves is clearly audible, but in other cases it is difficult to decide which bandwidth to select. , and it is uncertain whether that judgment is appropriate.

Therefore, in "Japanese Patent Application No. 55-130945 (Japanese Unexamined Patent Publication No. 57-55610)," the applicant proposed that the reception frequency control of a frequency synthesizer type receiver can be easily performed using a built-in microprocessor. We have described a receiver that can automatically select the optimal bandwidth by comparing the signal level of a desired signal with the signal level at nearby frequencies. However, in this case, a signal level detection means with a relatively wide dynamic range is required in the receiver, and calculations for relative comparison of the levels of the desired signal and the interfering signal are also required, so the circuit configuration is very large. It is complicated and expensive.

Therefore, the present invention solves these problems and
Immediately after the tuning operation to the frequency of the desired signal is completed, the degree of interference with the desired signal by nearby interfering signals is detected and the state is corrected, without detecting and comparing the signal levels of the desired signal and interfering signal individually. The present invention aims to provide a synthesizer receiver that can select the most suitable bandwidth according to the user's needs.

FIG. 1 is an explanatory diagram for explaining the principle of the present invention. If there is a sufficiently large interference signal in the vicinity of the desired signal located at frequency ₀ , the interference cannot be removed completely by the selectivity of the filter in the intermediate frequency amplification stage, resulting in large distortion in the reproduced signal. On the other hand, at this time, the DC component of the detected signal, which is the output of the FM detector, is V ₀ when there is only the desired signal, but moves to V ₁ due to the energy of the interference signal. Further, the amount of movement depends on the level ratio between the desired signal and the interference signal (hereinafter referred to as the D/U ratio). Therefore, by detecting the DC component of the FM detection signal in a state in which it is tuned to the desired signal frequency, the degree of the interference signal can be detected. However, this is not sufficient for practical use. That is, in a normal receiver, even if the level of the interfering signal is not high enough to cause a noticeable change in the DC component of the detected signal, a sufficiently large distortion will appear in the reproduced signal. In other words, it is difficult to detect disturbances more sensitively than the auditory detection limit and switch bands using the detection method based on the principle shown in FIG.

Therefore, the present invention uses a method of detecting the interference signal closer to the interference signal, as shown in FIG. First, set the receiving frequency of the receiver to desired signal frequency _0.
The frequency is set to ₀ + △, which is between the frequency and the frequency ' where there is an interfering signal that can affect this. If there is no interference signal or if the interference is negligible, the detected DC component will be _V2 , which is far from _V0 . However, if non-negligible interference exists at frequency ', the DC component is determined by the D/U ratio.
Move up to V ₃ . In this case, the influence of the desired signal and the interfering signal appear almost equally on the DC component, so
Extremely sensitive interference detection can be achieved. Therefore, a predetermined threshold value Vt ₁ is set for this DC component, and it can be determined whether or not the bandwidth should be switched depending on whether or not this value is exceeded. In Figure 2, the interference signal frequency is higher than the desired signal.
In the opposite case, the reception frequency may be set to ₀ - Δ, and the threshold value Vt ₂ may be set in the same manner to perform detection. Further, when the number of selectable bandwidths is three or more, it is sufficient to prepare a corresponding number of thresholds.

The reason why the degree of interference caused by the interference signal can be detected by detecting the DC component of the detection signal of the FM detector is as follows.

First, in FIGS. 1 and 2, the general pass characteristics of an intermediate frequency amplification stage are shown by broken lines. When a received signal and an interference signal exist in the state shown in Figure 1, the components in the shaded area pass through the intermediate frequency amplification stage and are combined in waveform form.
The signal is supplied to the FM detector and subjected to FM detection. At this time, since the interference signal component exists on the higher frequency side, the combined signal is essentially equivalent to a slight change in frequency toward the higher side, and the DC component of the detected signal is equal to the voltage at ₀ . It changes slightly from ₀ to the lower V ₁ depending on the influence.

On the other hand, if the receiving frequency is changed by △, the second
As shown in the figure, more components of the interference signal are contained within the passband of the intermediate frequency amplification stage. However, since the amplitude of the intermediate frequency amplification stage is limited by a limiter circuit, the total energy of its output signal is always constant, so the area of the shaded area is constant in both Figures 1 and 2. Become. Therefore, even if there is a desired signal and an interference signal similar to the case in FIG.
It will look like the solid line in the figure. As a result, the output signal whose waveforms have been combined will be very strongly affected by the components of the interference signal, and the DC component of the detected signal will be amplitude limited to a predetermined amplitude because only the desired signal of ₀ exists. It changes significantly from V ₂ when it is set to V 3 to V ₃ .

As is clear from the above explanation and the figure, the amount of change in the DC component of the detected signal from V ₂ to V ₃ changes according to the ratio of the amplitude of the interference signal to the desired signal, that is, the D/U ratio. However, the larger the interference signal, the larger the amount of change. It also changes depending on the frequency difference between the desired signal and the interfering signal.
In Figure 2, the smaller the frequency difference, the greater the rate at which the interfering signal enters the passband of the intermediate frequency amplification stage, whereas the substantial frequency change it exerts on the composite signal increases as the frequency difference increases. , the amount of change in the DC component is not necessarily uniquely determined. Note that when the frequency of the interfering signal is known in advance, it is most convenient if the frequency is moved to that frequency because the amount of change will be maximized.

Next, examples of changes in the DC component of the FM detection signal obtained through experiments are shown in FIGS. 6 and 7. In Figure 6, the desired signal is 83.0MHz, unmodulated, 60dBμV,
Assuming the interfering signal is 83.2MHz, 50% modulation (400Hz),
This is the characteristic when the D/U ratio is changed by changing the magnitude of the interference signal, and the solid line shows the receiving frequency.
The broken line shows the characteristics when the reception frequency is changed to 83.0MHz (corresponding to the case in Figure 1), and the characteristics when the receiving frequency is changed to 83.1MHz (i.e. △=100KHz) (corresponding to the case in Figure 1).
(corresponds to the case in the figure). As can be understood from the figure, in the case of the solid line, if Vt is the voltage at which the DC component drops by 1V from _V0 , it cannot be detected unless the interference signal has a D/U ratio of -26 dB or more, whereas in the case of the broken line, is the voltage whose DC component is 1V lower than _V2 .
If Vt is ₁ , the interference signal can be detected if the D/U ratio is about -1 dB or more, and an improvement of about 25 dB has been achieved.

Also, in Figure 7, the desired signal is 83.0MHz, unmodulated, 60dBμV, and the interference signal is 50% modulated (400Hz).
and the reception frequency is 83.1MHz (i.e. △
= 100KHz), this is the characteristic when the D/U ratio is changed by changing the magnitude of the interference signal (corresponding to the case in Figure 2), and the solid line is when the frequency of the interference signal is set to 83.2MHz. The broken line is the characteristic when the frequency of the interfering signal is 83.3MHz. As can be understood from the figure, in this example, the side where the interference signal is closer to the desired signal (solid line) is the smaller interference signal (−
1 dB or more), it is still detected. According to experiments, the frequency difference between the desired signal and the interfering signal is
At 200KHz, the best detection was achieved when △=100KHz.

Note that although the above experimental example is a case in which the interfering signal is a modulated signal, the same tendency is exhibited even in the case of an unmodulated signal.

FIG. 3 is a block diagram of an embodiment of a synthesizer receiver according to the present invention. Reference numeral 1 denotes a front end section, in which a reception frequency is set by a reception frequency control section 2. 3 is an intermediate frequency amplification section with a selectable bandwidth, and 4 is an FM detector. low pass filter 5
The DC component of the detected signal from the FM detector 4 is extracted and input to the voltage comparator 6. Bandwidth selection control section 7 selects the optimum bandwidth based on the output signal of comparator 6. In recent years, the reception frequency control section 2 is usually constituted by a microprocessor, and it is possible to include the function of the bandwidth selection control section 7 as part of its functions (as part of a program). be. In this case, the reception frequency control section 2 and the bandwidth selection control section 7 are integrated as a microprocessor 8.

FIG. 4 shows a specific configuration example of the voltage comparator 6, which is composed of two voltage comparator circuits 9 and 10 having threshold values of Vt ₁ and Vt ₂ (Vt ₁ > Vt ₂ ), respectively, and Q ₁ and outputs the _Q2 detection signal. In relation to Figure 2, for detection at ₀ +△, the input voltage is compared with Vt ₁ , and if there is no disturbance, the detection signal
Q ₁ is a low level, if it is, it is a high level. Next, in the detection at ₀ - Δ, the input voltage is compared with Vt ₂ , and if there is no disturbance, the detection signal Q ₂ becomes low level, and if there is, it becomes high level. However, if it is possible to set Vt ₁ =Vt ₂ depending on the characteristics of the receiver, only one comparator circuit is required.

Next, as described above, when the tuning function and the bandwidth selection function are executed by the microprocessor 8, how are the settings of the reception frequency, the reading of the detection signal of the voltage comparator 6, and the selection of the bandwidth performed? The procedure to be followed will be explained using the flowchart shown in FIG. However, here, there are two types of switchable bandwidths: wideband and narrowband. First, in step 11, it is repeatedly checked whether a new reception frequency has been set (or whether a new station has been selected). If a new receiving frequency is set, it will move to 12 "Wideband"
Choose. Next, in step 13, the reception frequency is set to ₀ + Δ, and in step 14, the detection signal _Q1 is read. 15
Check whether this detection signal _Q1 is low level or not,
If it is low level, that is, if there is no interference, it is 1.
Moving on to step 6, this time set the receiving frequency to ₀ - △. At step 17, the detection signal _Q2 is read, and at step 18, it is checked whether or not it is at a low level. Here, if the level is still low, it moves to 20 and starts reception at ₀ , and returns to 11 to wait for the next ₀ setting. On the other hand 1
When the detection signal Q ₁ is at a high level in step 5 or when the detection signal Q ₂ is at a high level in step 18, it is considered that interference has occurred, so in step 19 the mode is switched to "narrow band" and then the process moves to step 20.

Here, regarding the specific value of △, please refer to the general
In FM receivers, adjacent interference of ±200 and ±300KHz is a problem, so it is appropriate to choose Δ=100KHz.

As explained in the above embodiments, in the present invention, detection of nearby interference signals of the reception frequency is performed, for example, at _0.
Since it can be performed using only two points, +△ and ₀ -△, for example, the time required for detection at each receiving point is 0.1
If it is seconds, the normal reception state can be restored immediately after a total of 0.2 seconds. In addition, since the degree of interference is obtained from the DC component in the detected output, it can be configured simply by adding a voltage comparator, and selection decisions do not require calculations using complex programs, which is advantageous in terms of cost. This enables automatic bandwidth switching.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining the principle of interference signal detection according to the present invention, Figure 2 is a diagram for explaining the practical principle of interference signal detection according to the present invention, and Figure 3 is a diagram for explaining the practical principle of interference signal detection according to the present invention. FIG. 4 is a block diagram showing an example of the receiver, FIG. 4 is a diagram showing a specific configuration example of the voltage comparator, FIG. 5 is a diagram showing the procedure for automatic band switching, FIG.
FIG. 7 is a characteristic diagram showing the characteristics of a specific example according to the present invention. 4...FM detector, 6...Voltage comparator, 8...
Microprocessor, 9, 10... Voltage comparator circuit.

Claims (1)

[Scope of Claims] 1. A synthesizer receiver capable of selecting a plurality of different signal passing bandwidths, which includes: a detection means for detecting a DC component of a frequency detection signal obtained by frequency-detecting a received signal by a frequency detection means; means for selecting one of the plurality of bandwidths using the detection result of the means, and changing the reception frequency to a frequency near the desired signal frequency when the detection means detects the DC component. A synthesizer receiver characterized in that it has means for controlling a reception frequency. 2 When the desired signal frequency is ₀ , the receiving frequency is changed to ₁ +△ and ₀ -△ (where △ is the frequency change width) when detecting the DC component of the frequency detection signal. 1
Synthesizer receiver described in Section 1.