Method and apparatus for eliminating interference due to spurious signals generated in synthesized receivers

A method for eliminating spurious signal interference generated in a synthesized radio frequency (RF) signal receiver tuned to receive an RF signal from signal source;

• the RF signal receiver including first multiplying means for multiplying the RF signal and a first synthesizer signal to provide a first intermediate frequency (IF) signal, first filtering means having a predetermined frequency passband for filtering the first IF signal, second multiplying means for multiplying the filtered first IF signal from the first filtering means and a second synthesizer signal to provide a second intermediate frequency (IF) signal, second filtering means having a predetermined frequency passband for filtering the second IF signal, a signal source for providing a reference signal having a predetermined frequency, and synthesizing means coupled to the reference signal source for generating the first and second synthesizer signals, said method comprising the steps of:
• producing one of at least three pre-selected intermediate frequencies of the first IF signal;
• detecting that at least one of the first and second IF signals is modulated by a spurious signal;
• changing, in response to detection of spurious signal modulation, the frequency of the first and second synthesizer signals to produce another of the pre-selected intermediate frequencies of the first IF signal, whereby said RF signal receiver remains tuned to receive said RF signal and the spurious signal modulation is shifted outside the passband of the second filtering means.

A radio frequency (RF) signal receiver tuned to receive an RF signal from a signal source, comprising:

• first multiplying means for multiplying the RF signal and a first synthesizer signal to provde a first intermediate frequency (IF) signal having one of at least three pre-selected intermediate frequencies;
• first filtering means having a predetermined frequency passband for filtering the first IF signal, the frequency passband of the first filtering means including the three pre-selected intermediate frequencies of the first IF signal;
• second mutliplying means for multiplying the filtered first IF signal from the first filtering means and a second synthesizer signal to provide a second intermediate frequency (IF) signal having a pre-selected intermediate frequency;
• second filtering means having a predetermined frequency passband for filtering the second IF signal, the frequency passband of the second filtering means being less than the frequency passband of the first filtering means;
• a signal source for providing a reference signal having a predetermined frequency;
• synthesizing means coupled to the reference signal source and responsive to a control signal for generating the first and second synthesizer signals;
• means for demodulating the filtered second IF signal from the second filtering means;
• means coupled to the demodulating means for detecting spurious signals and generating an input signal when spurious signals have been detected;
• and
• control means responsive to the input signal for generating the control signal for changing the frequency of the first and second synthesizer signals to produce another of the pre-selected intermediate frequencies of the first IF signal, whereby said RF signal receiver remains tuned to receive said RF signal and the spurious signal modulation is shifted outside the passband of the second filtering means.

A radio frequency (RF) signal receiver tuned to receive an RF signal from a signal source, comprising:

• first multiplying means for multiplying the RF signal and a first synthesizer signal to provide a first intermediate frequency (IF) signal having one of at least two pre-selected intermediate frequencies;
• first filtering means having a predetermined frequency passband for filtering the first IF signal, the frequency passband of the first filtering means including the two pre-selected intermediate frequencies of the first IF signal;
• second multiplying means for multiplying the filtered first IF signal from the first filtering means and a second synthesizer signal to provide a second intermediate frequency (IF) signal having a pre-selected intermediate frequency;
• second filtering means having a predetermined frequency passband for filtering the second IF signal, the frequency passband of the second filtering means being less than the frequency passband of the first filtering means;
• a signal source for providing a reference signal having a predetermined frequency;
• first and second synthesizing means coupled to the reference signal source and responsive to first and second control signals for generating the first and second synthesizer signals, respectively;
• means for generating an input signal indicating that at least one of the first and second IF signals is modulated by a spurious signal;
• and
• control means responsive to the input signal for generating the first and second control signals for changing the frequency of the first and second synethesizer signals to produce another of the pre-selected intermediate frequencies of the first IF signal, whereby said RF signal receiver remains tuned to receive said RF signal and the spurious signal modulation is shifted outside the passband of the second filtering means.

A radio frequency (RF) signal receiver tuned to receive an RF signal from a signal source, comprising:

• first multiplying means for multiplying the RF signal and a first synthesizer signal to provide a first intermediate frequency (IF) signal having one of at least two pre-selected intermediate frequencies;
• first filtering means having a predetermined frequency passband for filtering the first IF signal, the frequency passband of the first filtering means including the two pre-selected intermediate frequencies of the first IF signal;
• second multiplying means for multiplying the filtered first IF signal from the first filtering means and a second synthesizer signal to provide a second intermediate frequency (IF) signal having a pre-selected intermediate frequency;
• second filtering means having a predetermined frequency passband for filtering the second IF signal, the frequency passband of the second filtering means being less than the frequency passband of the first filtering means;
• a signal source for providing a reference signal having a predetermined frequency;
• synthesizing means coupled to the reference signal source and responsive to a control signal for generating the first and second synthesizer signals;
• means for demodulating the filtered second IF signal from the second filtering means;
• means coupled to the demodulating means for detecting spurious signals and generating an input signal when spurious signals have been detected;
• and
• control means responsive to the input signal for generating the control signal for changing the frequency of the first and second synthesizer signals to produce another of the pre-selected intermediate frequencies of the first IF signal, whereby said RF signal receiver remains tuned to receive said RF signal and the spurious signal modulation is shifted outside the passband of the second filtering means.

A method for eliminating spurious signal interference generated in a synthesized radio frequency (RF) signal receiver tuned to receive an RF signal from a signal source;

• the RF signal receiver including first multiplying means for multiplying the RF signal and a first synthesizer signal to provide a first intermediate frequency (IF) signal, first filtering means having a predetermined frequency passband for filtering the first IF signal, second multiplying means for multiplying the filtered first IF signal from the first filtering means and a second synthesizer signal to provide a second intermediate frequency (IF) signal, second filtering means having a predetermined frequency passband for filtering the second IF signal, a signal source for providing a reference signal having a predetermined frequency, and synthesizing means coupled to the reference signal source for generating the first and second synthesizer signals;
• said method comprising the steps of:
• producing one of at least two pre-selected intermediate frequencies of the first IF signal;
• detecting that at least one of the first and second IF signals is modulated by a spurious signal;
• changing, in response to detection of spurious signal modulation, the frequency of the first and second synthesizer signals to produce another of the pre-selected intermediate frequencies of the first IF signal, whereby said RF signal receiver remains tuned to receive said RF signal and the spurious signal modulation is shifted outside the passband of the second filtering means.