JPH0253964B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for adjusting a band filter, and more specifically, to a method for easily adjusting a band filter to have good band pass characteristics (amplitude characteristics) without using special measuring equipment. This invention relates to a method for adjusting a band filter that can be adjusted to

[Conventional technology]

Conventionally, methods for adjusting the amplitude characteristics of a bandpass filter include a method using a spectrum analyzer 21 as shown in FIG. 8, and a method using a sweep generator 22, a detector 3, and an oscilloscope 2 as shown in FIG.
3, or a method using a standard signal generator 13, a wave detector 3, and a DC meter 4 as shown in FIG.

The method shown in FIG.
The oscillation output signal from the oscillation unit (tracking generator) is supplied to the input side of the bandpass filter 2,
The output signal of the band filter 2 is input to the analysis/display section of the spectrum analyzer 21, thereby directly displaying and monitoring the amplitude characteristics of the band filter 2 while changing the configuration of the resistor, inductor, etc. of the band filter 2. The elements are adjusted to give the bandpass filter 2 a desired amplitude characteristic.

In the method shown in FIG. 9, the oscillation output signal of the sweep generator 22 is input to the band filter 2, the output of the band filter 2 is detected by the detector 3, and then guided to the Y input of the oscilloscope 23. The output is led to the X input of the oscilloscope 23, whereby the amplitude characteristics of the bandpass filter 2 are displayed directly on the oscilloscope and variable components such as resistors and inductors of the bandpass filter 2 are adjusted while being monitored. 2 has a desired amplitude characteristic.

The method shown in FIG.
The output level of the bandpass filter 2 is detected by a detector 3 and a DC meter 4.
This method uses the method to adjust to the maximum value.
This method has the advantage that it does not require special measuring instruments such as the above-mentioned spectrum analyzer or oscilloscope, and can be adjusted relatively easily even outdoors.

[Problem that the invention seeks to solve]

The method using a spectrum analyzer or the like shown in Figure 8 and the method using an oscilloscope or the like shown in Figure 9 can obtain the best amplitude characteristics of the bandpass filter, but on the other hand, tracking
Generators, spectrum analyzers, sweep generators, etc. are currently expensive and heavy. Therefore, the environments in which these methods can be used are limited, and there are many cases where these methods cannot be used.

The method shown in Figure 10 is a simple method and can be easily carried out at any location. However, since the band filter 2 is adjusted so that the detection output is maximum at only the adjustment frequency (o), the adjustment The passband width of the subsequent bandpass filter tends to be narrow as shown in FIG. Although a wider bandpass width may be obtained by using a carrier wave offset from the center frequency of the bandpass filter, good characteristics may not necessarily be obtained depending on variations in the bandpass filter.

[Means for solving problems]

In order to solve the above-mentioned problems, in the present invention, a frequency modulation signal (FM signal) is supplied to the input side of a bandpass filter, the output level of the bandpass filter is detected, and the output level is maximized. A band filter adjustment method is provided for adjusting the band filter.

The frequency modulation signal has the center frequency (o) of the bandpass filter as the carrier wave frequency, the modulation frequency Δ not more than half the passband width of the bandpass filter, and 2Δ, which is twice the modulation frequency, as the carrier wave frequency. It is preferable that the width be one-half or more of the passband width of the filter. Further, it is preferable that the frequency modulation signal has a ratio of (d):Δ=10:7, where the frequency deviation is (d).

An example of the configuration of an apparatus for performing the band filter adjustment method according to the present invention is shown in FIG. In FIG. 1, the FM signal generator 1 includes a standard signal generator 13 that generates a carrier wave signal with an oscillation frequency corresponding to the center frequency (o) of the bandpass filter 2, and a modulated signal generator 13 that generates a modulated wave signal with a modulation frequency Δ. generator 11,
It also includes an FM modulator 12 that frequency-modulates the carrier signal from the standard signal generator 13 using the modulated wave signal from the modulated wave generator 11 with a frequency shift (d). Here, the relationship between the modulation frequency Δ and the frequency deviation (d) in the FM modulator 12 is (d):Δ=10:7.

A frequency modulated signal from an FM signal generator 1 is fed to the input side of a bandpass filter 2. A detector 3 and a DC meter 4 are connected to the output side of the bandpass filter 2 to measure its output level. Detector 3
Elements that can convert an input AC signal to a DC level, such as a linear detector, an envelope detector, or a rectifier/smoothing circuit, can be used.
As the DC meter 4, a DC voltmeter, a DC ammeter, or the like can be used.

Here, the relationship between the passband width W of the bandpass filter 2 and the modulation frequency Δ of the FM signal generator 1 is such that the modulation frequency Δ is less than or equal to half of the passband width W of the bandpass filter 2, and 2Δ is the width of the bandpass filter 2. This is more than one-half of the passband width W of No. 2. That is, the relationship is W/4≦Δ≦W/2.

[Effect]

The operation of adjusting the bandpass filter by the apparatus of FIG. 1 will be explained below with reference to FIGS. 2 and 3. FIG. 2 is a diagram showing the intended frequency/amplitude characteristics of the band filter 2, where the abscissa represents the frequency and the ordinate represents the output amplitude of the band filter. In the figure, (o) is the center frequency of the bandpass filter, W is the passband width of the bandpass filter 2, and Δ is the modulation frequency. Further, FIG. 3 is a diagram showing the spectrum of the frequency modulated signal from the FM signal generator 1.

The frequency modulated signal input from the FM signal generator 1 to the bandpass filter 2 has a carrier frequency of (o),
A frequency modulated signal having a frequency shift (d) of 10Δ/7 and having such a relationship has sideband waves as shown in FIG. 3, assuming that the amplitude of the carrier wave (o) is 1. In other words, the sideband wave (o) ±Δ has almost the same amplitude as the carrier wave (o), and the sideband wave (o)
±2Δ is approximately 0.4 times or less.

This frequency modulation signal is injected into the band filter 2, and in this state, the output level of the FM signal generator 1 is adjusted and fixed so that the pointer of the DC meter 4 has an appropriate deflection. Next, the adjustment points of the band filter 2 are adjusted so that the deflection of the pointer of the DC meter 4, that is, the output level of the band filter 2, is maximized.

Injecting a frequency modulated signal in this way results in the second
As is clear from the figure, the bandpass filter 2 has three carrier waves (o) and (o) with almost the same amplitude.
Since ±Δ is almost evenly distributed within the passband width of the bandpass filter 2 and is injected at the same time,
By adjusting the bandpass filter 2 so that the detection output is maximized, it is possible to obtain good amplitude characteristics that are substantially close to the desired characteristics shown in FIG.

The reason why 2Δ is set to more than half of the passband width W of the bandpass filter 2 is that the sideband (o) ±2Δ is set in the attenuation range of the amplitude characteristic shown in Fig. 2. This is to almost eliminate the influence of sideband waves (o) ±2Δ.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 shows an MCA (multi-channel access) radio receiver in which a band filter adjustment method according to an embodiment of the present invention is performed. In Fig. 4, 40 is an FM signal generator, the carrier wave frequency (o) is 855MHz, the modulation wave frequency Δ is 7kHz,
Outputs a frequency modulated signal with a frequency deviation (d) of 10kHz. 41 is an amplifier, an antenna or
An input signal is input from the FM signal generator 40.
The mixer 42 and the local oscillator 43 constitute the first stage frequency conversion circuit, and convert the 855MHz input signal to 55.025M
After converting to Hz, the signal is input to the band filter 44 which is to be adjusted by the method of the present invention. This band filter 44 has a pass band width W of 24 kHz.

The output signal of the bandpass filter 44 passes through an amplifier 45 and is then input to a second stage frequency conversion circuit consisting of a mixer 46 and a local oscillator 47, where the signal frequency is reduced to 455kHz. The output signal of the conversion circuit passes through a bandpass filter 48 and is input to an amplifier 49. The bandpass filter 48 has a passband width W of 16 kHz, and its amplitude characteristics have already been adjusted. The output signal of the amplifier 49 is divided into two parts, one of which is input to a speaker 52 via an FM demodulator 50 and an amplifier 51, and the other is input to a DC meter 54 via a wave detector 53.

As is clear from the above, the modulation wave frequency Δ (=7kHz) is less than 1/2 of the passband width of the bandpass filters 44 and 48, and 2Δ is 1/2 of the passband width of the bandpass filters 44 and 48. That's all.

When adjusting the band filter 44, the FM
Carrier frequency from signal generator 40 to amplifier 41
A frequency modulation signal of 855 MHz, modulation frequency of 7 kHz, and frequency deviation of 10 kHz is input, and the band filter 44 is adjusted so that the swing of the DC meter 54 is maximized.

5 to 7 show the reception band characteristics of the entire receiver shown in FIG. 4 using the 20 dB noise suppression method obtained by the adjustment method of the present invention and the conventional adjustment method, respectively. Fig. 5 shows the characteristics when using the method of the present invention, Fig. 6 shows the characteristics when using the sweep generator etc. shown in Fig. 9, and Fig. 7 shows the characteristics when using the standard signal generator and DC meter etc. shown in Fig. 10. .

As is clear from FIGS. 5 to 7, the best characteristics are those obtained by adjustment using a sweep generator, etc., as shown in FIG. The characteristics are comparable to those shown in FIG. 6, and are much better than those obtained by the simple adjustment method shown in FIG.

In the above embodiment, the detector 53 extracts the signal applied to the DC meter 54 from the amplifier 49, but the present invention is not limited to this.
The signal may be extracted directly from the output of the amplifier 45 or from the output of the amplifier 45.

〔Effect of the invention〕

According to the invention, a tracking generator;
Even without using expensive and heavy special measuring instruments such as spectrum analyzers or sweep generators, the amplitude characteristics of the bandpass filter can be adjusted to good characteristics with a simple configuration consisting of an FM signal generator, a detector, and a DC meter. It becomes possible. As a result, accurate adjustment of the amplitude characteristics of the bandpass filter can be easily performed relatively anywhere, and the cost of adjustment can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of a device for carrying out the band filter adjustment method of the present invention, Fig. 2 is a diagram showing the amplitude characteristics aimed at band filter adjustment, and Fig. 3 is the FM signal of Fig. 1. FIG. 4 is a diagram showing the spectrum of the frequency modulation signal of the generator, and FIG.
Figures 5 to 7 are diagrams showing the reception band characteristics of the Figure 4 receiver obtained by the method of the present invention and the conventional method, and Figures 8 to 10 are diagrams showing the reception band characteristics of the conventional band filter. Figure 11 shows the adjustment method for the 10th
It is a figure which shows the adjustment characteristic obtained by the figure method. 1...FM signal generator, 2...bandwidth filter, 3...
Detector, 4... DC meter, 11... Modulated wave generator,
12...FM modulator, 13...standard signal generator.

Claims (1)

[Claims] 1. Adjustment of a bandpass filter that supplies a frequency modulated signal to the input side of a bandpass filter, detects the output level of the bandpass filter, and adjusts the bandpass filter so that the output level is maximized. In the method, the frequency modulation signal has a center frequency (o) of the bandpass filter as a carrier frequency, a modulation frequency Δ not more than half the passband width of the bandpass filter,
A method for adjusting a bandpass filter in which 2Δ, which is twice the modulation frequency, is set to be one-half or more of the passband width of the bandpass filter. 2 The frequency modulated signal has a frequency deviation of (d)
The method according to claim 1, wherein (d):Δ=10:7.