JPH0730449A - Receiver - Google Patents

Abstract

PURPOSE:To reduce channel switching for avoiding interference by using plural filters having respectively different center frequency bands as receiving band limiting filters. CONSTITUTION:Three filters 8, 8a, 8b respectively having center frequency (f0), (f0+DELTAf), (f0-DELTAf) are prepared as filters for limiting receiving bands in an intermediate frequency circuit. Differences in receiving electric field intensity when a receiving signal is passed through respective filters 8, 8a, 8b are measured and the existence of an interference wave and the level of interference frequency are judged based upon the measured results. Where, f0 is intermediate frequency and DELTAf is prescribed frequency polarization. Thereby the existence of an interference wave and the level of interference frequency can be judged by any receiver of this kind independently of a modulation system, the degree of modulation and a return speed, an anti-interference characteristic can be improved by selecting filters whose interference quantity is furthermore reduced and channel switching for avoiding interference can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver of a radio system having a plurality of channels, and more particularly to improvement of interference resistance of the receiver.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing the structure of a double superheterodyne receiver.
Is a receiving antenna, and 2 is a high-frequency amplifier, which amplifies and filters a signal within the reception frequency band of this wireless system from the received signal. A first mixer 3 mixes the output from the high frequency amplifier 2 and the frequency from the first local oscillator 4 corresponding to the reception channel to obtain a first intermediate frequency signal. A first intermediate frequency amplifier 5 amplifies and filters the first intermediate frequency signal. 6 is a second mixer for amplifying and filtering the first intermediate frequency signal and the second
The frequencies from the local oscillator 7 are mixed to obtain a second intermediate frequency signal. Reference numeral 8 is a reception band limiting filter having a second intermediate frequency as a center frequency, 9 is an amplifier for amplifying a signal passed through the filter 8, 10 is a detection circuit for generating a DC voltage proportional to the received electric field strength, and 11 is a demodulation section. Is.

Next, the operation will be described. Although the operation of this type of receiver is well known, the signal received by the receiving antenna 1 passes through the high frequency amplifier 2, the first mixer 3, the first intermediate frequency amplifier 5, and the second mixer 6. , Center frequency f ₀
Of the second intermediate frequency signal. That is, signals other than the frequency band used in this wireless system are transferred to the high frequency amplifier 2
Signals other than the signal that is filtered and is not to be received even within the used frequency band are filtered by the first intermediate frequency amplifier 5 and the band limiting filter 8 to obtain the signal to be received at the frequency f ₀ . However, in the conventional receiver as described above, the signal of the frequency close to the frequency of the desired signal is
The band-limiting filter 8 cannot completely filter, and deteriorates the demodulation characteristics of the demodulation unit 11 as an interference wave.

[0004]

As described above, in the conventional receiver, the amount of interference resistance is determined by the attenuation characteristic of the band limiting filter, and when the demodulation characteristic is deteriorated by the presence of the interference wave, the communication channel is changed. Switching was done to avoid interference, and there was a waste of effective use of frequencies.

The present invention has been made in order to solve the above problems, and provides a receiver capable of reducing the channel switching for avoiding interference and improving the effective use of frequency by improving the interference resistance. The purpose is to do.

[0006]

In the receiver according to the present invention, as a filter for limiting a reception band in an intermediate frequency circuit, its center frequency is frequency (f ₀ ), frequency (f ₀ + Δf), frequency (f ₀ ). _0- Δf) is provided with three filters, the difference in received electric field strength when the received signal is passed through each filter is measured, and the presence or absence of an interference wave and the level of the interference frequency are determined from the measurement result. (However, f ₀ is an intermediate frequency and Δf is a predetermined frequency deviation).

Further, as a filter for limiting the reception band in the intermediate frequency circuit, the center frequencies are respectively (f ₀ + Δ
f) and (f ₀ −Δf) are provided, the difference in the received electric field strength when the received signal is passed through each filter is measured, and the presence or absence of the interference wave and the high and low of the interference frequency are measured from the measurement results. It is characterized by determining.

Further, it is characterized in that a predetermined threshold level is set and it is judged that an interference wave exists only when there is a difference exceeding this level.

Further, from the results of judging the presence or absence of an interference wave and the level of the interference frequency by these means, a filter having the least influence of the interference wave is selected from a plurality of filters and the signal passed through the filter is demodulated. Is characterized by.

Further, when the demodulation unit has an AFC function and the maximum deviation amount for which the AFC function is effective is ± Δf ₁ , the attenuation characteristics of a plurality of filters are made equal to each other, and It is characterized in that the maximum difference between the center frequencies is ± Δf ₁ .

[0011]

By configuring the receiver according to the present invention as described above, regardless of the modulation method, the modulation degree, and the transmission speed, the presence or absence of interference waves and the high and low interference frequencies are present in all receivers of this type. By selecting a filter that can be determined and has a smaller amount of interference, it is possible to improve the anti-interference characteristic and reduce the channel switching for avoiding interference. Further, deterioration of demodulation characteristics can be suppressed by the AFC in the demodulation unit.

[0012]

EXAMPLES Example 1. Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention, which is an example implemented in a double superheterodyne type receiver. In FIG. 1, reference numeral 1 is a receiving antenna, and 2 is a high-frequency amplifier, which amplifies and filters a signal within the receiving frequency band of this wireless system. 3 is the first mixer,
The output from the high frequency amplifier 2 and the frequency from the first local oscillator 4 corresponding to the reception channel are mixed to obtain a first intermediate frequency signal. A first intermediate frequency amplifier 5 amplifies and filters the first intermediate frequency signal. A second mixer 6 mixes the amplified and filtered first intermediate frequency signal and the frequency from the second local oscillator 7 to obtain a second intermediate frequency signal.

Reference numeral 8 is a reception band limiting filter having a second intermediate frequency (hereinafter referred to as f ₀ ) as a center frequency, 8a is a reception band limiting filter having a center frequency as f ₀ + Δf, 8
b is a reception band limiting filter having a center frequency of f ₀ −Δf, 9 is an amplifier for amplifying the signal from the reception band limiting filter 8, 9a is an amplifier for amplifying the signal from the filter 8a, and 9b is from the filter 8b. An amplifier for amplifying the signal of 10 is a detection circuit for generating a DC voltage proportional to the received electric field strength of the output from the amplifier 9, and 10a is an amplifier 9a.
A detection circuit for generating a DC voltage proportional to the received electric field strength of the output from the amplifier 10b, a detection circuit for generating a DC voltage proportional to the received electric field strength of the output from the amplifier 9b, 11
Is a demodulation unit corresponding to the modulation system of the wireless system, and AFC
With the (Automa-tic Frequency Control) function, this AF
Assuming that C has a good demodulation characteristic for a received signal up to a frequency deviation of f ± Δf ₁ , the filters 8a, 8
The Δf of b is configured to match the Δf ₁ of this AFC. When the demodulator 11 is a demodulator that demodulates a frequency-modulated wave, the center frequency of the frequency discriminating circuit is often not f ₀ . In such a case, a local oscillator is provided in the demodulator 11 to convert the center frequency of the signal from f ₀ to the center frequency of the frequency discriminating circuit for demodulation. When the center frequency of the signal deviates from f _{0, the} frequency discriminating circuit detects this deviation, and the demodulation unit 11 uses the detected deviation.
The oscillation frequency of the local oscillator in the inside may be feedback-controlled. 21 is a changeover control circuit, 22 is a changeover switch,
As will be described later, the presence or absence of an interference wave and the amount of interference are determined from the output of each amplifier 10, 10a, 10b,
Of the outputs of the amplifiers 9, 9a, 9b, the output least affected by the interference wave is connected to the demodulation unit 11.

Next, the operation will be described. FIG. 2 is a diagram showing an example of frequency characteristics of the reception band limiting filters 8, 8a, 8b. As shown in the figure, the filters 8, 8a, 8b are shown.
Have the same characteristics except that the center frequencies differ by Δf. Here, the outputs of the amplifiers 9, 9a, 9b are temporarily S0, S +, S-, and the detection circuits 10, 10a, 10b.
Assuming that the output of E is E0, E +, E-, if there is no interference wave in the received signal and only the desired signal frequency is obtained, the measured value of the received electric field strength becomes E0> E + = E-, which causes the switch 22 selects the output S0 of the amplifier 9.

If an interference wave is present in the received signal,
For example, when there is an interference wave with a frequency higher than the desired signal frequency, the measured value of the received electric field strength is E +>E0> E.
-, Which causes the switch 22 to select the output S- of the amplifier 9b. The output S- of the amplifier 9b is the filter 8
Due to the frequency characteristic of b, the frequency higher than that of the filter 8 is limited by Δf. Therefore, the interference wave of higher frequency is filtered by this filter 8b, and only the desired signal frequency is input to the demodulation unit 11. The demodulation unit 11 has the AFC function having a good demodulation characteristic for the received signal up to the frequency deviation of f ± Δf ₁ as described above, and therefore the attenuation characteristics of the filters 8, 8a, 8b are made equal to each other. ,
And the maximum difference between the center frequencies of these filters is ±
By setting Δf ₁ , it is possible to suppress the deterioration of the demodulation characteristics by this AFC, and thus to obtain a demodulated signal that is less affected by the interference wave.

On the contrary, when an interference wave having a frequency lower than the desired signal frequency is present, the measured value of the received electric field strength is E->E0> E +, and the switch 22 causes the amplifier 9 to operate.
By selecting the output S + of a, similarly, a demodulated signal less affected by the interference wave can be obtained. Even if there is no interference wave, depending on the content of the received signal, E- and E +
Therefore, a threshold level that is recognized as a significant difference is actually set in advance, and if there is a difference that exceeds this level, it is judged that there is an interference wave, the above operation is performed, and it must be exceeded. For example, if S0 is selected as no interference wave, more stable operation can be performed.

Example 2. In the first embodiment, the filter-amplifier-detector circuit is composed of three sets. However, as shown in FIG. 3, the switches 221 and 222 that operate before and after the three filters 8, 8a and 8b are provided. Alternatively, the amplifier 9 and the detector 10 may be provided in common. In this case, in order to monitor the interference wave, the switching control unit 211 switches the switches 221 and 222 in a time division manner, stores the received electric field strengths when passing through the respective filters, and performs the above-mentioned comparison. Select the appropriate filter from.

Example 3. Further, the switch 221 may be omitted in the configuration of the second embodiment. This configuration is shown in FIG. In this case, the switching control unit 211 sequentially switches the inputs of the switch 222, compares the output changes of the detector 10, and selects the input that minimizes the output of the detector 10.

Example 4. In the first embodiment, the filter-amplifier-detector circuit is composed of three sets. However, two filters 8a and 8b are sufficient to determine the presence or absence of an interference wave, and when there is no interference wave. , Whether selecting filter 8a or filter 8b by the AFC function,
Since the demodulation performance is the same as when the filter 8 is selected, the configuration of the filter-amplifier-detection circuit is
It is also possible to use two sets of a-amplifier 9a-detection circuit 10a and filter 8b-amplifier 9b-detection circuit 10b, and omit the filter 8-amplifier 9-detection circuit 10. This structure is shown in FIG.

[0020]

As described above, according to the present invention, the presence or absence of an interference wave and the level of the interference frequency can be discriminated by using three filters having different center frequencies as the reception band limiting filters.

Further, according to the result of this discrimination, by selecting the filter with the smallest amount of interference and demodulating, the anti-interference characteristic is improved, and there is an effect that the frequency can be effectively used.

The receiver of the present invention can be implemented irrespective of the modulation method, modulation degree, and transmission rate.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing frequency characteristics of a filter according to the present invention.

FIG. 3 is a block diagram showing a second embodiment of the present invention.

FIG. 4 is a block diagram showing a third embodiment of the present invention.

FIG. 5 is a block diagram showing a fourth embodiment of the present invention.

FIG. 6 is a block diagram showing an example of a configuration of a conventional receiver.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 receiving antenna 2 high frequency amplification part 3 1st mixer 4 1st local oscillator 5 1st intermediate frequency amplifier 6 2nd mixer 7 2nd local oscillator 8,8a, 8b reception band limiting filter 9,9a, 9b amplifier 10, 10a, 10b Detection circuit 11 Demodulation unit 21 Changeover control circuit 22 Changeover switch 211 Changeover control unit 221, 222 Changeover switch

Claims (5)

[Claims] 1. As a filter for limiting a reception band in an intermediate frequency circuit, its center frequency is a frequency (f
₀ ), frequency (f ₀ + Δf), and frequency (f ₀ −Δf) (where f ₀ is an intermediate frequency and Δf is a predetermined amount of frequency deviation), three filters are provided, and the received signal is passed through each filter. A receiver comprising means for measuring a difference in received electric field strength at the time, and determining the presence or absence of an interference wave and the level of the interference frequency from the measurement result. 2. As a filter for limiting a reception band in an intermediate frequency circuit, when the intermediate frequency is f ₀ and a predetermined amount of frequency deviation is Δf, the center frequency is (f ₀ + Δ).
f) and (f ₀ −Δf) are provided, and the difference in received electric field strength when the received signal is passed through each filter is measured. From the measurement result, the presence or absence of an interference wave and the high and low of the interference frequency are measured. A receiver having means for judging. 3. The means for determining the presence or absence of an interference wave based on the difference in the electric field strength sets a predetermined threshold level, and determines that the interference wave exists only when there is a difference exceeding this level. The receiver according to claim 1 or 2. 4. A means for demodulating a signal passed through the filter by selecting a filter having the least influence of the interference wave from the plurality of filters based on the result of the presence / absence of the interference wave and the level of the interference frequency determined by the means. The receiver according to claim 1, 2, or 3, characterized in that. 5. AFC (Automatic Frequency Control)
When the maximum displacement amount that has a function and this AFC function is effective is ± Δf ₁ , the attenuation characteristics of the plurality of filters are made equal to each other, and the maximum difference between the center frequencies of these filters is f. 5. The receiver according to claim 4, wherein ₀ ± Δf ₁ is set.