JP2614551B2 - Electric field strength monitoring receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field strength monitoring receiver used in a radio base station of an automobile telephone system.

[0002]

2. Description of the Related Art A radio base station of an automobile telephone is provided with a receiver for monitoring the electric field strength, and a radio line connection and a radio channel management of a radio zone of a mobile station moving between a number of radio zones in a control area. For this reason, the reception electric field strength (radio wave intensity) of radio waves from a mobile station having a large number of channels of several hundred channels is detected in a short time. FIG. 1 is a block diagram showing a part of a receiver to which the present invention is applied. A received wave f _R from a mobile device is input to a mixer 2 via a high frequency stage (RFA) 1. In order to detect the intermediate frequency signal f _I of many channels to be monitored in a short time, the local oscillator 3
Is supplied to the mixer 2 by switching the output frequency f _L at high speed.

As the local oscillator 3, a frequency synthesizer (hereinafter, referred to as a synthesizer) using a voltage controlled oscillator (VCO) is used to perform frequency switching at high speed. The synthesizers used here include a single synthesizer for high-speed switching and a dual synthesizer combining two synthesizers, each having advantages and disadvantages. That is, the technical point is the harmony of the conflicting characteristics that the S / N is deteriorated when the sensitivity (easiness of pull-in) is increased by shortening the frequency switching time. In FIG. 1, reference numeral 4 denotes an intermediate frequency amplification stage (I
FA). Reference numeral 5 denotes a detector which can obtain an output indicating the electric field strength of the received wave. Reference numeral 6 denotes a control unit such as a microprocessor that controls the entire receiver, and supplies a control signal for frequency switching to the local oscillator 3.

FIG. 2 is a block diagram of the local oscillator 3 of FIG. 1, showing an example of a dual synthesizer system in which two synthesizers are combined. FIG. 3 is a block diagram of a synthesizer using a PLL using a VCO. The VCO 13 is controlled by controlling the frequency division ratio of the frequency dividers 11 and 12 by a control signal.
Output frequency is set. Although the above-mentioned single synthesizer cannot make the frequency switching time zero in principle, the switching time can be made zero in the dual synthesizer system of FIG. That is, the output from the # 1 synthesizer 7 of the frequency designated by the control signal is switched to the switch S
While the local oscillation frequency f _{L is} being output by W, the frequency of the other # 2 synthesizer 8 is switched to the next frequency. When the switching is completed, the switch SW is switched to output the output from the # 2 synthesizer to the local oscillator 3. Output. Practically, the frequencies of the two synthesizers are switched almost simultaneously, and the output whose output is stabilized first is switched by the switch SW.
Take out by. The feature of this method is that the time required for frequency switching can be made sufficiently longer than that of the single synthesizer method, so that the deterioration of S / N is small.

[0005]

However, in the above-mentioned dual synthesizer system, for example, when the power is turned on, the frequencies of the two synthesizers are controlled to the same frequency, or the adjacent synthesizers such as 6.25 kHz or 12.5 kHz are used. The frequency may be controlled, and in the case of the former (the same frequency), a beat frequency is generated due to a mutual phase difference due to interference between VCOs or a difference in interference path, thereby causing S / N deterioration of the receiver. In the latter case (proximal frequency), since the IF passband gain of the receiver is high, mutual interference occurs and spurious signals are generated. FIG. 5 is an explanatory diagram showing a path of mutual interference in the dual synthesizer. In the figure, indicates direct interference between VCOs, indicates interference between output wirings of the VCO, and indicates that the output of the buffer amplifier is VCO
Is the interference path.

In order to reduce the influence of the mutual interference, it is necessary to increase the interval between the two synthesizers or provide an electromagnetic shield. However, at present, small-sized receivers do not have a space for widening the arrangement interval and are provided with three or four layers of shields, and the shield effect is not sufficient. SUMMARY OF THE INVENTION An object of the present invention is to provide an electric field strength monitoring receiver which solves the above-mentioned problems at once, and which is compact and does not require a shield.

[0007]

SUMMARY OF THE INVENTION An electric field strength monitoring receiver according to the present invention receives radio waves of a predetermined number of radio channels, switches the frequency of a local oscillator, and sequentially converts the frequency into an intermediate frequency signal by a mixer. In the electric field intensity monitoring receiver for converting and detecting the electric field intensity of the multiple waves based on the detection output, the local oscillator switches the outputs of the first synthesizer, the second synthesizer, and the first and second synthesizers. The first synthesizer is provided with a switch control signal such that the output frequency of the first synthesizer becomes a frequency obtained by adding the intermediate frequency to the frequency of the received radio wave. Switching control so that the output frequency of the second synthesizer becomes a frequency obtained by subtracting the intermediate frequency from the frequency of the received radio wave. Is characterized in that the output after switching frequency of the first and second synthesizers are provided a control unit for controlling to switch the switch alternately from the one in which stable giving No..

[0008]

FIG. 1, FIG. 2, and FIG. 3 are block diagrams showing respective circuits to which the present invention is applied, and FIG. 4 is a timing explanatory diagram showing a control signal of a local oscillator 3 according to the present invention and its operation. That is, the control signal for setting the frequency of the # 1 synthesizer is different from the control signal for setting the frequency of the # 2 synthesizer. For the # 1 synthesizer, the intermediate frequency f _I is added to the frequency f _R of the radio wave to be monitored sequentially. set the frequency, # for 2 synthesizer sets the frequency obtained by subtracting the intermediate frequency f _I from a radio wave of a frequency f _R for sequentially monitoring. Then, while the output of the synthesizer whose switching has been completed is used as the output of the local oscillator 3, the frequency of the other synthesizer is switched and the switch SW is controlled so as to output the output of the local oscillator 3 when the switching is completed. , And so on. Although the control signal may be supplied separately from the control unit 6, two control signals may be supplied serially.

By performing the above control, the frequencies of the two VCOs are 2f _I even if the two synthesizers are set to the same frequency or adjacent channel frequency without changing the intermediate frequency f _I of the receiver. No mutual interference occurs because of the distance between
Even if the シ ー ル ド quadruple shield is changed to a very simple shield, the improvement effect of S / N degradation of 10 to 15 dB at the same frequency setting and the improvement effect of spurious generation amount of 15 to 20 dB are obtained.

[0010]

As described in detail above, by implementing the present invention, S / N degradation and spurious generation are small even when high-speed frequency switching is performed with a simple shield, and miniaturization and economical efficiency are achieved. The receiver can be realized with a great effect.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a main part of an embodiment of the present invention.

FIG. 3 is a block diagram showing some details of an embodiment of the present invention;

FIG. 4 is a timing explanatory diagram of the embodiment of the present invention.

FIG. 5 is an explanatory view showing a conventional defect.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 RFA 2 Mixer 3 Local oscillator 4 IFA 5 Detector 6 Control unit 7, 8 Synthesizer 11, 12 Divider 13 VCO

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasuo Sera 2-3-13 Toranomon, Minato-ku, Tokyo International Electric Company (72) Inventor Michio Norikachi 2-3-1 Toranomon, Minato-ku, Tokyo International Inside Electric Co., Ltd. (72) Inventor Masataka Nozaki 2-3-13 Toranomon, Minato-ku, Tokyo International Electric Co., Ltd. (72) Katsunori Hamada 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation Examiner Kazuo Kuna (56) References JP-A-63-111741 (JP, A) JP-A-61-102564 (JP, A)

Claims (1)

(57) [Claims] 1. A radio wave of a predetermined multi-wave radio channel is received, the frequency of a local oscillator is switched, the signal is sequentially converted into an intermediate frequency signal by a mixer, and the electric field strength of the multi-wave is detected by a detection output. In the electric field strength monitoring receiver, the local oscillator includes a first synthesizer, a second synthesizer, and a switch that switches an output of the first and second synthesizers to output a local oscillator, and the first synthesizer To the second synthesizer, the output frequency of the first synthesizer becomes a frequency obtained by adding the intermediate frequency to the frequency of the received radio wave, and the output frequency of the second synthesizer is supplied to the second synthesizer. Of the first and second synthesizers by providing a switching control signal such that the frequency becomes the frequency obtained by subtracting the intermediate frequency from the frequency An electric field strength monitoring receiver, comprising: a control unit that controls the switching so that the switch is alternately switched from the one in which the output after switching is stable.