JPS638659B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a space diversity receiving device that switches between two antennas and receives the one with a better reception condition, and more specifically, a selection determination circuit that determines which one has a better reception condition. Regarding.

A conventional space diversity receiver is shown in FIG. Conventionally, the electric field of the radio wave induced in the antenna 1 is detected by a level detector 11, and the detected signal is sampled and held by a sample and hold circuit 12 that samples and holds the detected signal at the clock timing from a clock pulse generation circuit 15. The state of the radio wave induced in the antenna 2 is detected in the same manner as described above by switching in a well-known manner, and the level of the detected signal and the sample-and-hold signal are compared, and the antenna with a better reception state is selected and received.

However, conventionally, even if the current receiving antenna is in good condition, the antenna is switched once and the receiving condition of the other antenna is determined. There are drawbacks that occur. Also, conventionally antennas 1 and 2
Since we are only comparing the reception status of each moment,
It has the disadvantage that it is prone to malfunction due to excessive antenna switching, etc.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a space diversity receiving apparatus that eliminates the above-mentioned conventional drawbacks and can satisfactorily perform antenna switching decisions.

An embodiment of the present invention will be described below with reference to FIG. In the same figure, 1 and 2 indicate antennas, and the signals induced in the antennas are transferred to the antenna switching circuit 3.
The selection switching signal enters the high frequency amplifier 4, is selectively amplified, is converted to an intermediate frequency by the mixer 5, and is sent to the intermediate frequency amplifier 6,
The signal is guided to a speaker 9 via an FM detector 7 and a low frequency amplifier 8. Reference numeral 11 indicates a level detector that detects a part of the signal from the intermediate amplifier 6, and the level of the signal detected by the detector changes in proportion to the strength of the radio wave. 16 is a low-pass filter that obtains the average value of this variation, and 17 is a lower detector. This lower detector 17 has a quick response when the signal decreases, but
Since the rise is slow, it is possible to cut out noise when the electric field temporarily increases due to noise when switching antennas. The output signal of this detector 17 is guided to a comparator 13. Reference numeral 18 denotes a filter that removes components of 19 kHz or less from the output of the level detector 11 and passes the others. The signal that has passed through the filter enters the detector 19, where it becomes a direct current. As is well known, when the filter 18 is disturbed by multi-path reflections while the radio waves are transmitted from the broadcasting station to the antenna, the strength of the radio waves changes.
An AM component is generated in the output of the level detector 11.
Also, the 19kHz pilot portion of this AM component is
Since the modulation degree of the pilot signal is fixed by regulation, a good correlation with multipath distortion can be obtained. This has been confirmed through actual measurements, so the filter is centered around 19kHz, and this level is proportional to the amount of multipath. This signal is converted into a DC signal by a wave detector 19 and supplied to a determination circuit 20, which generates a trigger signal when the DC level is equal to or higher than a set level set by the determination circuit 20. 21
indicates a sensitivity switching circuit, and when the radio waves become weak, AM components are generated due to the radio's self-noise.
Since malfunctions occur, the determination level of the determination circuit 20 is increased in a weak electric field to prevent malfunctions. When a trigger signal is generated from the determination circuit 20, the sample hold circuit 12 operates and holds the level of the output signal of the lower detector 17. Thereafter, antenna switching is performed as described below. The antenna switches and its state is applied to comparator 13 as before.
The transient state at this time is the lower detection circuit 17 (actually
(consisting of an emitter follower detection circuit using a PNP transistor). In this way, the comparator 13 compares the output of the sample hold circuit 12 and the output of the lower detection circuit 17, which is the level after switching, and if the output of the lower detection circuit 17 is large, the antenna as it is is used. hold,
Next, the operation is stopped until a trigger signal is received from the determination circuit 20 again. If the sample and hold circuit 13 is larger, a signal is generated from the comparator 13 to the hold circuit 14 so as to return the antenna to the original antenna 1, and the antenna switching circuit 3 is operated. This operation is maintained until a trigger signal is received from the determination circuit 20 next. In this way, by switching the antenna only when multipath occurs, the generation of noise due to the switching is reduced, and at the same time, the state of the radio waves can be determined correctly, allowing reception with low multipath distortion and noise. ,can.

If the antenna is switched only when multipath occurs, as in this embodiment, the frequency of switching can be reduced, and the noise based thereon can be reduced. Furthermore, when switching antennas, if the reception condition of that antenna is poor, the antenna is switched again to the original antenna, so there is no inconvenience such as continuing to receive radio waves from the antenna side with poor reception condition.

According to the present invention described above, since the antenna can be selected and switched correctly, there is an effect of reducing multipath noise, skip noise, etc. of the FM car radio.

[Brief explanation of the drawing]

FIG. 1 shows a block diagram of a conventional space diversity determination circuit. FIG. 2 shows a block diagram of an improved decision circuit according to the present invention. 1...Antenna, 2...Antenna, 3...Antenna switching circuit, 4...High frequency amplifier, 5...Mixer, 6...Intermediate frequency amplifier, 7...FM detector, 8...Low Frequency amplifier, 9...Speaker, 1
0... Local oscillator, 11... Level detection, 12...
...Sample hold circuit, 13...Comparator, 14
...Hold circuit, 15...Clock, 16...
Low-pass filter, 17...lower detection circuit, 1
8... Filter, 19... Detection circuit, 20...
Judgment circuit, 21...Sensitivity switching circuit.

Claims (1)

[Claims] 1. A first antenna, a second antenna, an antenna switching circuit that selects one of the antennas and guides a received signal induced in the selected antenna to a reception regeneration circuit, and an antenna switching circuit coupled to the reception regeneration circuit. , a detection circuit that detects a level signal proportional to the received signal, a sample hold circuit that samples and holds the detection signal of the detection circuit when it receives a control signal (pulse), and a hold signal of the sample hold circuit and the detection circuit of the detection circuit. a comparison circuit for comparing detection signals; and an antenna switching control circuit coupled to the comparison circuit, receiving the control signal, and supplying an antenna switching control signal to the antenna switching circuit when the detection signal is smaller than the hold signal. In the space diversity method, the detection circuit is coupled to the sample and hold circuit, the comparison circuit, and the antenna switching control signal generation circuit, and when the AM component of the detection signal of the detection circuit exceeds a predetermined level, An AM component detection circuit detects an AM component, and upon receiving a detection signal from the AM component detection circuit, generates the control signal, and supplies the control signal to the sample hold circuit, comparison circuit, and antenna switching control signal generation circuit. 1. A space diversity receiving device characterized by being provided with a control signal generation circuit that performs a control signal generation circuit. 2. The AM component detection circuit is coupled to the detection circuit, and includes a filter that passes frequencies around 19 kHz, a detector that detects the frequency that has passed the filter and obtains a DC signal, and a detector that detects the level of the DC signal of the detector. 2. The space diversity receiving device according to claim 1, further comprising a determining circuit which determines the level of the signal and when the level reaches a predetermined level or higher, activates the control signal generating circuit to generate a pulse.