Method and circuit for avoiding band interference wave in receiver
First Claim
1. A method of avoiding a band interference wave which is produced in a receiver when a reception frequency used for radio communication is converted into a fixed intermediate frequency by using an oscillation frequency of a local signal oscillator, comprising the steps of setting bandwidths of a plurality of bandpass filters for dividing a band of reception frequencies such that a frequency of a band interference wave produced by the oscillation frequency of the local signal oscillator falls outside a pass band, and switching one of the plurality of bandpass filters to a bandpass filter corresponding to the frequency of the reception signal.
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Abstract
In a method of avoiding a band interference wave which is produced in a receiver when a reception frequency used for radio communication is converted into a fixed intermediate frequency by using the oscillation frequency of a local signal oscillator, when the frequency of a reception signal is on the low-frequency side in a reception frequency band, channel setting and route switching control are so performed as to make the reception signal pass through a low-pass filter. A circuit for avoiding a band interference wave is also disclosed.
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Citations
5 Claims
- 1. A method of avoiding a band interference wave which is produced in a receiver when a reception frequency used for radio communication is converted into a fixed intermediate frequency by using an oscillation frequency of a local signal oscillator, comprising the steps of setting bandwidths of a plurality of bandpass filters for dividing a band of reception frequencies such that a frequency of a band interference wave produced by the oscillation frequency of the local signal oscillator falls outside a pass band, and switching one of the plurality of bandpass filters to a bandpass filter corresponding to the frequency of the reception signal.
- 3. A circuit for avoiding a band interference wave which is produced in a receiver when a reception frequency used for radio communication is converted into a fixed intermediate frequency by using an oscillation frequency of a local signal oscillator, comprising bandpass filters for dividing the band of reception frequencies into a plurality of narrow bands, and a switch for switching said bandpass filters in accordance with a reception frequency of a reception signal corresponding to a set channel, wherein said plurality of bandpass filters respectively have frequency characteristics which set bandwidths such that a frequency of a band interference wave produced by the oscillation frequency of said local signal oscillator falls outside a pass band.
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5. A circuit for avoiding a band interference wave which is produced in a receiver when a reception frequency used for radio communication is converted into a fixed intermediate frequency by using an oscillation frequency of a local signal oscillator, comprising:
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a plurality of bandpass filters which divide a band of reception frequencies into a plurality of narrow bands, and respectively have bandwidths set such that a frequency obtained by adding a frequency ½
the intermediate frequency to a lowest reception frequency in each band falls outside a pass band;
a switch for switching said bandpass filters in accordance with a reception frequency; and
a local signal oscillator for generating a fixed intermediate frequency by changing a generated oscillation frequency in accordance with a reception frequency.
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Specification