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US 4,286,221 AGranted
Multi-frequency signal receiving apparatus
AssigneeHitachi, Ltd.
InventorKazuhiko Takaoka
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AssigneeHitachi, Ltd.
InventorKazuhiko Takaoka
Estimating the term…
A multi-frequency signal receiving apparatus for receiving signals with at least more than two frequencies and selectively separating these signals, comprising a first maximum value detecting means for detecting the maximum value of the rectified outputs of a plurality of channel filters provided for said signals to be selected; a second maximum value detecting means for detecting the maximum value of the rectified outputs at the intermediate stage of two channel filters for discriminating the signals at both ends of the signal frequency bands of a plurality of said channel filters; and a comparison means for comparing the outputs of said first and second maximum value detecting means with an appropriate weight and thereby detecting the presence or absence of the signal to be detected; whereby based on the result of comparison, the threshold value of discriminators placed at the succeeding stage of said channel filters for discriminating the predominant frequency signal is controlled. The invention thus permits the elimination of input filers, and realizes an economical and reliable signal receiver.
A multi-frequency signal receiving apparatus which receives multi-frequency input signals, separates and selects said multi-frequency input signals comprising,
Dependencies are inferred from the claim text.
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Using multi-frequency signalling: in which m-out-of-n signalling frequencies are transmitted
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Term ended 3 Oct 1999 (estimated)
USPTO file history isn’t available for this patent, so only indexed dates are shown.
This invention relates to a multi-frequency signal receiving apparatus, and more particularly to a multi-frequency signal receiving apparatus which receives plural input signals with different frequencies, discriminates and converts them into d.c. output signals, and sends these output signals to plural output points in accordance with the frequencies of the input signals.
Before the explanation of this invention in comparison with a prior art, a brief explanation will be made of the drawings, in which:
FIG. 1 is a block diagram showing a prior art multi-frequency signal receiving apparatus;
FIG. 2 is a block diagram showing one embodiment of a multi-frequency signal receiving apparatus according to this invention;
The constitution of a prior art multi-frequency signal receiving apparatus is as shown in FIG. 1, in which waves with different frequencies arrive at an input terminal IN and then enter a common main band-pass filter MBPF. The MBPF selects a signal group in a required frequency band from a signal outside this band, the latter being either mixed in the input signal or coming independently thereof. The outputs of the MBPF are made to enter the channel band pass filters CHBPF 1, 2, . . . , 6 provided for each frequency band. Each CHBPF detects a wave in a selected band from the input signal frequency group and sends only the due component to the output. The output of each CHBPF 1, 2, . . . , 6 is connected to the input of each discriminator DIS 1, 2, . . . 6 having a fixed threshold and the output is compared with the above fixed threshold and it is also compared with the output information of a later-mentioned signal detection circuit SDC.
The output of the MBPF is also connncted to a signal detection circuit in order to control the signal timing system of the receiver. When the output of the MBPF exceeds a preset threshold level, the SDC generates a pulse train in response to the output of the MBPF, rectifies and shapes. After a predetermined delay time the d.c. signal is sent to the DIS 1, 2, . . . , 6.
Accordingly, after the d.c. signal comes from the SDC, the DIS 1, 2, . . . , 6 convert the outputs of the CHBPF 1, 2, . . . , 6 into pulse signals with two values, rectify and shape them, and send them to output terminals OUT 1-6.