Telecommunications – Receiver or analog modulated signal frequency converter – Noise or interference elimination
Patent
1981-08-12
1983-07-26
Bookbinder, Marc E.
Telecommunications
Receiver or analog modulated signal frequency converter
Noise or interference elimination
328167, 333 17R, 455307, H04B 112
Patent
active
043957790
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a jamming wave rejecting device for rejecting jamming waves of a single frequency present in a receiving frequency band or in its vicinity in a receiver of a relatively wide receiving frequency band.
BACKGROUND ART
For example, in a Loran C receiver, electric waves of a Decca navigation system (hereinafter referred to as the Decca electric wave) may sometimes lie in the vicinity of its receiving frequency band. For rejecting this Decca electric wave, a narrow-band rejection filter, which is what is called a notch filter, is employed. A vessel loaded with the Loran C receiver sails passing through areas of Decca electric waves of different frequencies, so that when it enters an area in which the frequency of the Decca electric wave jamming reception differs from that in the previous area, it is necessary to adjust the center frequency of the abovesaid narrow-band rejection filter to accurately set it to the jamming wave. Since the rejection filter is to reject the jamming wave in the vicinity of the receiving band or in the receiving band, its rejection band designed to be narrow; accordingly, the operation of adjusting its center frequency to the frequency of the jamming wave is very difficult and much time and skill are required for the adjustment; in addition, even if this adjustment contains a slight deviation, the presence of this rejection filter rather rejects a portion of the signal component desired to receive and the jamming wave rejecting effect extremely lessens, making it impossible to achieve the desired object. The jamming wave to the Loran C receiver, the Decca electric wave in general, may sometimes exist not only at one frequency but also at a plurality of frequencies and it was very troublesome to adjust the center frequency of the narrow-band rejection filter for each of them. In ordinary receivers as well as in the Loran C receiver, the adjustment for rejecting the jamming wave by a narrow-band rejection filter was very cumbersome and demanded time and skill.
An object of this invention is to provide a jamming wave rejecting device which is designed so that when the frequency of a narrow-band rejection filter is brought to the neighborhood of the jamming wave to be rejected, the center frequency of the narrow-band rejection filter automatically and accurately coincides with the frequency of the jamming wave, thus enabling rejection of the jamming wave easily and accurately.
DISCLOSURE OF THE INVENTION
According to this invention, the narrow-band rejection filter is arranged so that its rejection center frequency may be controlled by a control signal; signals on the input and output sides of the narrow-band rejection filter are taken out utilizing the general property of the narrow-band rejection filter that the phase of its output corresponding to the input signal becomes a leading phase or a lagging phase with respect to the input signal depending upon whether the frequency of the input signal is above or below the center frequency of the filter; the phase difference between the signals taken out is detected; and the center frequency of the narrow-band rejection filter is controlled by the detected output so that the center frequency may automatically coincide with the frequency of the jamming wave accurately. In this case, since a linear portion of the phase characteristic of the narrow-band rejection filter is very narrow, the output from the narrow-band rejection filter is provided via a band-pass filter to an indicator and the pass center frequency of the band-pass filter is controlled by a control signal so that the indicator may indicate a maximum value, that is, the pass center frequency of the band-pass filter may substantially coincide with the center frequency of the jamming wave. By the control signal at that time is controlled the rejection center frequency of the narrow-band rejection filter. In this case, the same control characteristic is used for the both filters, by which the center frequency of the band-pass filter for
REFERENCES:
patent: 3293572 (1966-12-01), Smith
patent: 3562675 (1971-02-01), Urell
patent: 3715690 (1973-02-01), Young et al.
patent: 3787774 (1974-01-01), Tietze et al.
Chiwaki Kenichi
Fujino Teruhisa
Narazaki Sadatoshi
Osawa Fujio
Bookbinder Marc E.
Kabushiki Kaisha Koden Seisakusho
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