JPS5928093B2 - receiving device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a receiving apparatus having two intermediate frequency amplifiers having different band characteristics, and a receiving apparatus including a device for automatically switching between the two intermediate frequency amplifiers according to reception conditions.

In general, in FM receivers, when dealing with nearby station interference signals or interference waves, it is better to narrow the band of the intermediate frequency amplifier (hereinafter referred to as IF amplifier) and increase the selectivity to eliminate mixed interference signals. However, the distortion of the demodulated signal increases and the sound quality deteriorates.

Further, when using a wide band, it is advantageous in reducing distortion and improving sound quality, but it becomes susceptible to mixed interference. Therefore,
In order to satisfy the above-mentioned mutually contradictory factors, conventionally, an IF amplifier having two band characteristics, a wide band characteristic and a narrow band characteristic, is provided, and the switching is performed manually or automatically depending on the receiving condition. However, manual switching is not practical because the receiver must check for the presence or absence of an interference signal before switching, and automatic switching requires comparing the output level detected by an interference signal detector with a predetermined level. However, in such a configuration, the narrowband IF amplifier is also used when the interfering interference components are not reduced even if the narrowband is used, such as pulse noise such as ignition noise, noise at weak input, etc. Since the signal was switched between the two, it was not possible to receive the signal in the best possible condition.
The present invention relates to automatic switching of intermediate frequency amplification and provides a device that eliminates the above-mentioned drawbacks.Embodiments of the present invention will be described below with reference to the drawings. The radio waves received by the antenna 1 are converted into an intermediate frequency by the front end 2 and input to the wideband IF amplifier 3a and the narrowband IF amplifier 3b. The outputs of the wideband and narrowband IF amplifiers 3a and 3b are F
The signals are demodulated by M detectors 4a and 4b, respectively. When interference signals such as proximity interference signals and pulse noise are mixed, FM
Noise components occur in the detection output. The noise components are detected by high-pass filters 5a, 5b and AM detectors 6a, 6.
b converts it into a DC signal. T is a comparator, which compares the two output levels from the AM detectors 6a and 6b, and when the output level of the AM detector 6a is higher than the output level of the AM detector 6b, that is, the FM detector on the wide band side 4
An output signal is generated only when the noise component of a is greater than the noise component of the narrowband side FM detector 4b, and is input to the switching circuit 8. The switching circuit 8 switches to the narrow band only when an output is generated from the comparator 7, and otherwise switches to the wide band. If a proximity interference signal occurs, F
Since a wideband bead component is generated in the M detection output by the proximity interference signal and the desired station, the output level of the wideband side AM detector 6a is higher than the output level of the narrowband side AM detector 6b. Therefore, an output signal is generated from the comparator 7, which causes the switching circuit 8 to switch to the narrow band side. Furthermore, with respect to pulse noise such as ignition noise, since the outputs of both the AM detectors 6a and 6b are at the same level,
No output is generated from the comparator 7, so the switching circuit 8 is switched to the broadband side. Also, in normal reception conditions where no noise such as a proximity interference signal or pulse noise occurs, the output level from the AM detectors 6a and 6b is zero, so the switching circuit 8 switches to the wideband side as described above. . FIG. 2 shows input level vs. S/N ratio characteristics when a wideband 1F amplifier is used and input level vs. S/N ratio characteristics when a narrowband 1F amplifier is used.

At the time of weak input, the S/N ratio also deteriorates as the input level decreases. However, when the input level is between a and b, the AM detectors 6a and 6b have the same output level because the S/N ratio is the same for both the input level and the input level.
Therefore, by switching the switching circuit 8, wideband 1F
Reception is performed by amplifier 3a. If the input level further decreases and becomes lower than point a, the S/N ratio will be larger for the same human power level than for A, and therefore the output level of AM detector 6a will be lower than that of AM detector 6b. The signal becomes larger than the output level, an output signal is generated from the comparator 7, and the switching circuit 8 puts the narrowband IF amplifier 3b into a receiving state. As described above, according to the present invention, when the reception condition can be improved by switching the bandwidth of the intermediate frequency amplifier,
In other words, it detects proximity interference signals and automatically switches to a wideband or narrowband 1F amplifier to achieve the best reception condition, and reduces the intermediate frequency bandwidth in case of pulse noise or weak input. It has an identification function that switches to wideband reception when the reception condition cannot be improved even after switching, and also switches to wideband reception even in normal conditions where noise components such as the proximity interference signal and pulse noise are not generated. This makes it possible to receive data in the optimal state at all times.

[Brief explanation of drawings]

FIG. 1 is an embodiment of the present invention, and FIG. 2 is a diagram showing input level versus S/N ratio characteristics of wideband and narrowband intermediate frequency amplifiers. 1...Antenna, 2...Front end, 3a...
・Wideband intermediate frequency amplifier, 3b... Narrowband intermediate frequency amplifier, 4a, b... FM detector, 5a, b... High pass filter, 6a, b... AM detector, 7... Comparison device, 8... switching circuit, 9... FM multiflex demodulator.

Claims (1)

[Claims] 1 a first intermediate frequency amplifier having wideband characteristics; a first detector that detects the output of the first intermediate frequency amplifier;
a second intermediate frequency amplifier having narrowband characteristics; a second detector for detecting the output of the second intermediate frequency amplifier; and an interference distortion signal and pulse nature contained in the demodulated signal of the first detector. a first interference signal detection means for detecting the magnitude of a noise component such as noise; and a first interference signal detection means for detecting the magnitude of a noise signal such as an interference distortion signal or pulsed noise contained in the demodulated signal of the second detector. a comparison means for comparing the output levels of the second interference signal detection means and the first and second interference signal detection means;
switching means controlled by the output from the comparing means, and when the comparing means detects a predetermined level difference or more, the switching means is controlled to change the output of the first or second intermediate frequency amplifier. A receiving device characterized in that: selectively passes through a transmission system.