JPS627727B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a receiver automatic tuning method that automatically matches the output frequency of a signal generator with the reception frequency of a receiver under test in a receiver characteristic test. .

When testing the characteristics of a receiver, it is necessary to match the output frequency of the signal generator and the reception frequency of the receiver prior to measurement. A tuning operation to adjust the frequency is essential, but conventionally it has been common to manually adjust the receiver so that the demodulated output is maximized. Systems have also been proposed in which measuring instruments are controlled by an electronic computer or the like to automate measurements, but in that case too, the tuning operation of the receiver under test must be performed manually.

As mentioned above, the tuning operation is performed by finding the point where the demodulated output of the receiver under test is at its maximum. However, the rate of change in the demodulated output due to detuning near the tuning point is not very large, so in order to detect the maximum output point, that is, the tuning point, careful operation is required when observing the instructions of the measuring instrument. This requires a considerable amount of time, and it is also difficult to find the tuning point with high precision.

In order to improve these drawbacks, the present inventor has proposed an "AM receiver automatic tuning method" (Japanese Patent Application Laid-Open No. 1983-92050) for AM receivers, but this method does not require AM signal generation. Since it is characterized by giving a frequency transition of a constant period to the signal generator output, a special frequency transition device must be added to the signal generator.
It has the disadvantage that a normal AM signal generator cannot be used as is. For FM receivers as well, the present inventor has proposed an "FM receiver automatic tuning method" (Japanese Patent Laid-Open No. 1983-92051), but this method is based on the non-linear part of the frequency discrimination characteristic of the FM receiver under test. Therefore, in order to perform highly accurate tuning, the frequency discrimination characteristics of the test receiver must be symmetrical with respect to the tuning point, including the non-linear part, but normal FM Since symmetry including non-linear parts is not considered in the receiver, the tuning point according to this method has the disadvantage that it does not exactly match the true tuning point of the receiver under test.

The present invention improves the conventional drawbacks as described above, and utilizes the fact that the differential value or difference value with respect to the reception frequency of the delay time given to the modulated signal by the test receiver becomes zero at the tuning point, The objective is to automatically control the frequency of the signal generator or receiver under test so that this differential value or difference value becomes zero. Examples will be described in detail below.

FIG. 1 is a block diagram of an embodiment of the present invention, in which an output signal in a radio frequency band modulated by the output of a modulation signal source 2 is transmitted from a signal generator 1 to a test receiver 4 via a variable attenuator 3. It can be added to the antenna terminal etc.

The demodulated output of the receiver under test 4 is applied to the signal detection section 5 together with the output of the modulated signal source 2, and the output is proportional to the differential value or difference value with respect to the receiving frequency of the delay time of the demodulated output with respect to the output of the modulated signal source. Drive the motor 6. The motor 6 is coupled to the output frequency adjustment mechanism of the signal generator 1, and the signal detector 5
By rotating until the output of the signal generator 1 becomes zero and stopping, the output frequency of the signal generator 1 is automatically made to match the receiving frequency of the receiver under test 4.

Figure 2 is an explanatory diagram of the delay time given to the modulated signal component by the receiver under test, and Figure 2a shows an example of the selection characteristic α and phase shift characteristic β of the receiver under test, with the tuning frequency f ₀ as a reference. . Here, the reception frequency, 2b is the passband width, ₀ +b is the upper limit frequency of the passband,
₀ -b is the lower limit frequency of the passband. As is clear from the figure, the phase shift characteristic is within the passband, that is,
In the range ₀ + b >> ₀ - b, it changes approximately in proportion to the change in the detuning frequency - ₀ , centered around the tuning frequency ₀ , but the upper limit of the passband is ₀ +
The rate of change increases as it approaches b and the lower limit ₀ - b, and the attenuation band outside the passband, i.e. > ₀ +
In general, the value is approximately constant in the band b and the band < ₀ - b.

FIG. 2b shows the delay time given to the modulated signal component by the phase shift characteristic shown in FIG. 2a. The solid line in the figure shows that when a modulated wave with a frequency spectrum of +b and -b is applied to the test receiver 4, as shown in the lower part, in which the frequency carrier wave is amplitude-modulated with a modulation signal of frequency b, the modulated signal component b The delay time given is shown with respect to the receiving frequency or detuning frequency - ₀ , and as is well known, the delay time is the difference between the phase shift for the carrier wave and the phase shift for the sideband divided by the modulation frequency. As shown in the figure, the maximum value β ₁ /b is reached at the tuning point ₀ , that is, the detuning frequency ₀ , and the characteristic is a single peak that decreases in a substantially symmetrical manner with respect to 0. The dotted line in the figure shows the case where a modulated wave with a frequency spectrum of +b/2 and -b/2 is applied to the receiver under test 4, as shown in the lower part, in which the frequency carrier wave is amplitude-modulated with a modulated wave of frequency b/2. The delay time given to the modulation signal component b/2 is similarly shown. In this case, as shown in the figure, the minimum value is reached at the tuning point ₀ , and ₀ + b/2 and ₀ -
The maximum value is shown at b/2 > ₀ + b/2 and <
In the range ₀ - b/2, it exhibits a bimodal characteristic that decreases in a substantially symmetrical manner with respect to ₀ .

FIG. 3 shows the voltage obtained by differentiating the delay time characteristic shown in FIG. 2b with respect to the reception frequency. Corresponding to the case of modulation frequency b shown by the solid line in Fig. 2b, the third
As shown by the solid line in the figure, an S-shaped characteristic is obtained, which becomes zero at tuning point ₀ , and approaches zero after passing through one maximum value or minimum value, respectively, in approximately point symmetry with respect to this zero point.

Also, corresponding to the case of modulation frequency b/2 shown by the dotted line in Fig. 2b, the tuning point is shown by the dotted line in Fig. 3.
₀ , and approaches zero through a pair of local maximum and minimum values, approximately symmetrical to this zero point 3
Obtain a property with zero crossing points.

In this way, the differential value of the reception time with respect to the detuning frequency is zero at the tuning point ₀ , and changes approximately linearly with respect to the detuning frequency near the tuning point, > ₀
It has a characteristic that the polarity is reversed in the region of 0 and the region of < ₀ . Such a characteristic voltage is extracted as the output of the signal detection section 5 and applied to the motor 6 which is directly connected to the frequency adjustment mechanism of the signal generator 1, so that the motor is always driven in the direction where the detuning frequency becomes zero. By selecting the polarity, a frequency control system using a known negative feedback closed loop method can be constructed. As a result, the motor is controlled so as to always stop at the point where the output of the signal detector 5 is zero, that is, the tuning point ₀ , so the output frequency of the signal generator 1 is always automatically set to the tuning frequency ₀ of the receiver under test 4. It is possible to match the

However, in the case of modulation frequency b/2, that is, in the case of the characteristic shown by the dotted line in Fig. 3, ₀ +b/2>>
It is necessary to consider that the negative feedback closed loop control system is constructed only within the range of ₀ - b/2.

The signal detection section 5 has a function of detecting the delay time between the output of the modulated signal source 2 and the demodulated output of the receiver under test 4, and extracting this as a differential value or a difference value with respect to the receiving frequency. Specifically, the delay time is defined as the time between detecting corresponding specific points (for example, the point at which each output waveform passes the zero point) between the output waveform of the modulation signal source 2 and the demodulation output waveform of the receiver under test 4. is detected by known analog or digital time measurement techniques. Further, the reception frequency is detected by a known analog or digital frequency measurement method.

In order to differentiate the delay time detected in this way with respect to the reception frequency, the delay time is detected every cycle of the modulated signal and the difference from the detected value immediately before (that is, one cycle before) is extracted each time. Ru.

The reception frequency is detected at the same time as the delay time is detected. That is, it is sampled and detected every cycle of the modulated signal. Similarly to the detection of delay time, it is configured to extract the difference from the detected value immediately before (that is, one cycle before) each time.

In this way, the change in delay time between one cycle of the modulated signal and the change in reception frequency during the same period are extracted. Then, the signal obtained by dividing the change in delay time by the change in reception frequency is taken out as the output of the signal detection section 5, and used for controlling the frequency adjustment section as described above. For division in this case, a known analog or digital division method is used.

Normally, when measuring the characteristics of a receiver, the receiving frequency does not change rapidly during one cycle of the modulated signal, so the output of the signal detection section 5 can be considered to be the differential value of the delay time with respect to the receiving frequency. . However, if the sampling period is set to a large value that is an integral multiple of the modulation signal period for some reason, the output of the signal detection section 5 becomes a difference value of the delay time with respect to the receiving frequency, but the basic tuning operation remains the same.

Although an embodiment is shown in which a motor is coupled to a frequency adjustment mechanism as the frequency control means of the signal generator 1, other purely electrical frequency control means may be provided and controlled by the output of the signal detection section 5. .

Alternatively, the output frequency of the signal generator 1 may be fixed, and the receiver under test 4 may be provided with a frequency control means to perform automatic tuning.

As modulation frequencies, b and b/2 are used in the embodiment, but any single or composite frequency can be used as long as a signal detector output having the characteristics necessary for control can be obtained. be able to.

Further, although the embodiments are shown for amplitude modulation, the same applies to frequency modulation.

As explained above, the present invention provides the test receiver 4
The signal detection unit 5 detects the differential value or difference value of the delay time given to the modulated signal with respect to the reception frequency, and controls the frequency adjustment function of the signal generator 1 or the receiver under test 4 so that the value becomes zero. and
Since the signal detecting section 5 uses a method of detecting a zero point with polarity reversal, it is more accurate than a method of detecting a maximum value, and the tuning point can be detected in a short time.

In addition, the differential value or difference value of the delay time with respect to the receiving frequency is not essentially changed by any of the modulation method, the local oscillation frequency arrangement of the receiver under test 4, and the demodulated output polarity. The same tuning scheme can be used regardless of the scheme and type.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG.
FIGS. a to b are explanatory diagrams of the delay time given to the modulated signal component by the receiver under test, and FIG. 3 is an explanatory diagram of the differential value of the delay time with respect to the detuning frequency. 1 is a signal generator, 2 is a modulation signal source, 3 is a variable attenuator, 4 is a receiver under test, 5 is a signal detection section, and 6 is a motor.

Claims (1)

[Claims] 1 In the method of measuring the characteristics of the receiver by applying the output of the signal generator to the receiver under test via an attenuator,
comprising a signal detection unit having a function of detecting a delay time between a modulated input signal applied to the signal generator and a demodulated output signal of the receiver under test, and outputting this as a differential value or a difference value with respect to the reception frequency, A receiver automatic tuning method characterized by controlling a signal generator or a frequency adjustment section of a receiver under test so that the output of the signal detection section becomes zero.