JPH0493775A - Measuring device of reception frequency - Google Patents

Abstract

PURPOSE:To enable quick and accurate detection of the frequency of an input signal by a method wherein an output from a switch conducting selection and switching of an output of a mixer and an output of an oscillator is subjected to frequency-voltage conversion. CONSTITUTION:A local signal oscillator 1 oscillates a local signal fLO fro the frequency fR of an input signal. A switch 4 being selected onto the oscillator 3 side, two reference frequencies f1 and f2 are inputted and subjected to conver sion from frequencies into voltages V1 and V2 and the frequency-to-output characteristic of a frequency discriminator 5 is determined. The voltages V1 and V2 are stored in a memory 7. The switch 4 being selected onto the mixer 2 side, next, an output voltage V of the discriminator 5, the frequencies f1 and f2 and the voltages V1 and V2 are substituted in the equation and thereby an intermediate frequency fIF is determined. Since the frequency of the local oscillator 1 is fixed for the input signal, the frequency of the input signal fR can be determined by fR = fLO - fIF without necessitating a time for drawing n the frequency of the local oscillator such as an AFC circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a received frequency measuring device that can quickly and accurately receive a frequency and analyze its frequency components.

[Prior art] In a received frequency measuring device, AFC is used to stabilize the frequency of a local oscillation signal by using the DC component of the demodulated signal of a frequency discriminator.
A circuit is provided.

The AFC circuit controls the frequency of the local oscillator signal using the output from the frequency discriminator so that the human input signal is centered in the selected bandwidth, and detects the frequency of the input signal.

When the selected frequency band width of the input signal is narrow, for example, 50 KHz or less, a crystal can be used for the frequency discriminator, and as a result, the temperature drift characteristics can be highly stabilized.

However, in a radio wave monitoring device, for the purpose of monitoring illegal radio waves, the selected frequency bandwidth of the input signal is
A wide band of about MH2 is required. Since a crystal with a narrow bandwidth cannot be used in such a wideband frequency discriminator, a frequency discriminator composed of a resistor and a capacitor (hereinafter referred to as RC) is used.

However, the frequency discriminator using RC does not have good temperature drift characteristics. Therefore, for example, even if the output voltage of a frequency discriminator is adjusted to be 0 at the center frequency of the selected band, the output voltage will change due to temperature changes, causing a shift in the center frequency, resulting in illegal radio waves. The output frequency of the device is measured incorrectly.

Therefore, AF that does not depend on the temperature drift of the frequency discriminator
The invention of the C circuit is disclosed (Utility Model Publication No. 59-3419)
(Refer to No. 8), to explain the outline of this invention, first, a signal of a reference frequency is input to a frequency discriminator only for a specific period. Next, the output of the frequency discriminator at that time, ie, the output error voltage due to temperature drift, is stored. And A.F.
When constructing the C loop, errors due to temperature drift are removed by controlling the voltage controlled oscillator based on the difference between the output of the frequency discriminator and the previously stored voltage.

[Problem to be solved by the invention]

However, even with the AFC circuit devised above, problems still remain.

That is, in the AFC circuit, the problem inherent to the AFC circuit that it takes a certain amount of time to acquire the frequency of the local oscillator signal has not been solved at all.

This problem will be explained below.

In the AFC circuit, the comparator 10 converts the DC component voltage of the demodulated signal from the frequency discriminator into the basic lightning voltage, for example, when the input frequency of the frequency discriminator (hereinafter referred to as intermediate frequency)
If the DC component voltage is higher than this reference voltage, the voltage will be lowered, and if the DC component voltage is lower than the base Y$ voltage, the voltage will be increased. , it is necessary to correct the frequency fLO of the local oscillator signal, and the correction is performed so that the DC component voltage matches the reference voltage.

As a result, if the circuit system is up-conversion, the frequency fR of the target input signal is the value obtained by subtracting fIF from fLO after correction, that is, fR = f LO - f IF
obtained by.

However, the time required for correction (for example, lock amplifier time in the case of a local oscillator signal) is naturally necessary, and this time cannot be eliminated.

[Means to solve the problem]

In order to solve the above problems, the present invention employs the following means.

The configuration of the apparatus of the present invention will be explained using FIG.

The local signal oscillator 1 oscillates a local signal fLO with respect to the frequency fR of the input signal.

Mixer 2 mixes the frequency fR of the input signal and the frequency fLO of the local signal from local signal oscillator 1 to produce an intermediate frequency signal fIF.

Oscillator 3 oscillates a reference frequency to frequency discriminator 5.

A switch 4 switches between the signal from the mixer 2 side and the signal from the oscillator 3.

The frequency discriminator 5 converts the intermediate frequency r IF or the reference frequency into a voltage V.

A/D converter 6 converts the output voltage of frequency discriminator 5 from an analog signal to a digital signal.

The memory 7 stores digital data in which the reference frequency is converted into voltage.

The calculation unit 8 calculates the characteristics of the frequency discriminator 5 checked using the reference frequency stored in the memory 7 and the intermediate frequency f IF.
The frequency fl? of the input signal is determined by the voltage V of the input signal and the local frequency fLO. Calculate.

The control section 9 controls the memory 7 and the calculation section 8.

The operation of the apparatus of the present invention will be described in detail below.

Select the switch 4 to the oscillator 3 side, and select the two reference frequencies f1.
, f2, the frequencies f1 and f2 are converted from frequencies to voltages v1 and v2, and the frequency discriminator 5
Find the frequency vs. output characteristics of.

Next, the voltages ν1 and v2 are stored in the memory 7, respectively.

Next, the switch 4 is selected to the mixer 2 side, and the output voltage ■ of the frequency discriminator and the above-mentioned frequencies fl, f2 and vl, v2 are selected.
Substitute into the formula below.

Vl-V2 Vl-V2 Then, as a result of calculating the equation, the intermediate frequency fIF can be found.

In the device of the present invention, since the frequency of the local oscillator is fixed with respect to the input signal, fR=
The frequency of the input signal fR can be found from fLO-fIF.

Furthermore, in this device, even if a temperature drift occurs in the frequency discriminator 5, the frequency fR of the input signal can be determined because the straight line of the frequency versus output characteristic is determined from the two reference frequencies f1 and f2.

〔Example〕

The configuration of the present invention will be explained using FIG. 1.

a local signal oscillator 1; a mixer 2 that converts the frequency of an input signal using the local signal; an oscillator 3 that generates two reference frequencies; a switch 4 that selects between the output of the mixer 2 and the output of the oscillator 3; A frequency discriminator 5 that converts the output from the switch 4 into a frequency voltage, an A/D converter 6 that converts the output from the frequency discriminator 5 from analog to digital, and a first reference frequency f1 and a second reference frequency f2. A memory 7 stores the outputs 1 and v2 of the A/D converter 6 corresponding to the outputs 1 and 2 of the A/D converter 6, and a memory 7 stores the outputs v1 and v2 of the A/D converter 6, and the switch 4 The control section 9 stores the outputs of the A/D converters in the memory, and the frequency vs. output characteristics of the frequency discriminator 5 are determined by the output from the memory 7. At the same time, the switch 4 is selectively switched to the input signal side, and the frequency fR of the input signal is calculated from the output from the A/D converter 6 at that time and the frequency fLO of the local signal. 8.

Next, the procedure for determining the frequency of a human input signal according to the present invention will be explained using FIGS. 1 and 2.

(1) First, the switch 4 is switched to the oscillator 3 side that oscillates the reference frequencies f1 and f2.

(2) The frequency discriminator 5 converts the reference frequencies f1 and f2 into corresponding voltages v1 and v2, respectively.

(2) After converting voltages v1 and v2 from analog signals to digital signals, each is stored in memory.

(2) Switch the switch 4 to the mixer 2 side, convert the frequency fR of the input signal, and input it to the frequency discriminator 5.

0 frequency discriminator 5 converts the frequency into voltage, and substitutes the voltage (■) into the following equation.

Vl-V2 Vl-V2■ By calculating the above equation, the intermediate frequency fIF is determined.

■Then, from the intermediate frequency flF and the predetermined frequency fLO of the local signal, fR= fLO
The frequency of the input signal fR is determined by calculating fIF.

Even if a temperature drift occurs in the zero frequency discriminator 5,
According to the reference frequencies f1 and f2, the corresponding voltage VIT,
By determining V2T, the frequency versus output characteristic can be determined, and the frequency of the input signal can be determined from this (see FIG. 2).

As another example, a superheterodyne system in which the mixer 2 is arranged in multiple stages is of course also effective.

In addition, by switching the frequency of the local signal oscillator 1 in steps for each selected band, the receiver can handle a wide range of bands, storing illegal radio waves detected in a certain band, continuing scanning, and later detecting illegal radio waves. It is also possible to check radio waves.

Further, in the embodiment of the present invention, the calculation is performed in the calculation unit 8, but it is also possible to obtain the frequency of the input signal by providing a table in the memory and substituting the voltage value of the input signal into it. becomes.

Furthermore, in the embodiment of the present invention, two reference signals are input and their frequency vs. voltage characteristics are calculated, but if the linearity of the frequency vs. voltage characteristics of the frequency discriminator 5 is poor, three or more points are measured. Of course it is possible to do so.

[Effects of the Invention] First, it has become possible to quickly and accurately detect the frequency of an input signal. As a result, it is effective in detecting illegal radio waves that disappear instantly.

Next, since the output from the frequency discriminator is A/D converted, it can be processed by the CPU as digital data.

Furthermore, even a frequency discriminator using a crystal is not completely free from temperature drift, and if this method is used, the received frequency can be measured with higher accuracy.

[Brief explanation of drawings]

Fig. 1 shows the configuration of the device of the present invention, Fig. 2 shows the characteristics of the frequency discriminator of the invention, and Fig. 3 shows the conventional AF
It is a diagram showing the configuration of a C circuit.・Local signal oscillator, 2...Mixer, ・Oscillator, 4...Switcher, ・Frequency discriminator, 6...A/D converter, ・Memory, 8
...Arithmetic section, -Control section, 10...Comparator.

Claims (1)

[Claims] a local signal oscillator, a mixer that converts the frequency of an input signal using the local signal, an oscillator that generates at least two first and second reference frequencies, and a switch that selects and switches between the output of the mixer and the output of the oscillator. a frequency discriminator that converts the output from the switching device into a frequency voltage; an A/D converter that converts the analog signal output from the frequency discriminator into a digital signal; a memory that stores the outputs of the A/D converters corresponding to the two reference frequencies; and a control unit that stores the outputs of the A/D converters when the switch is selectively switched to the oscillator side. , calculates the frequency versus output characteristic of the frequency discriminator based on the output from the memory, and calculates the frequency vs. output characteristic of the frequency discriminator, and the output from the A/D converter and the frequency of the local signal when the switch is selectively switched to the mixer side. and a calculation unit that calculates the frequency of the input signal from the input signal.