Instrument landing system receiver monitor

Claim 2

In a radio receiver system of the type separably recovering first and second tonal modulation components on a received carrier signal; said receiver comprising means for amplitude detecting said tonal modulation components, tone bandpass filtering means receiving the output of said means for detecting and producing first and second output signals comprising said demodulated tones, means for rectifying the outputs from said filtering means and applying DC signals respectively proportional to the difference in aMplitude of said tonal modulation components to an indicating means; a monitoring means for detecting malfunction in said receiver and annunciating same, said monitoring means comprising a tracer signal source, means for amplitude modulating said received carrier signal by said tracer signal, further bandpass filtering means connected to the output from said tone bandpass filtering means and passing a signal corresponding in frequency to that of said tracer signal, a first phase detector receiving the output of said further bandpass filtering means as a first input thereto, said tracer signal source comprising a second input to said first phase detector, low pass filtering means receiving the output of said first phase detector, means for controlling the frequency of said tracer signal source as a function of the output of said low pass filtering means, and annunciating means being connected to and activated in response to a predetermined threshold output from said low pass filtering means.

Claim 3

A receiver system as defined in claim 1 including means for phase locking said tracer signal source to a frequency to which said first and second outputs from said bandpass filtering means are equally responsive.

Claim 4

A system as defined in claim 2 wherein said tracer signal source operates at a frequency substantially equal that of the mean of said demodulated tone frequencies.

Claim 5

A receiving system as defined in claim 3 wherein said means for modulating comprises means to vary the impedance of a carrier frequency selective circuit preceding any active element in said receiving means.

Claim 6

A receiving system as defined in claim 4 further comprising a third bandpass filtering means centered at the frequency of said tracer signal source and receiving the output of said receiver amplitude detector, said third bandpass filtering means output being applied as a first input to a second phase detecting means, said tracer signal source comprising a second input to said second phase detecting means, and said annunciating means being connected to and additionally responsive to a predetermined amplitude threshold of the output from said second phase detecting means.

Claim 7

A receiving system as defined in claim 5 wherein said annunciating means is connected to and additionally responsive to a predetermined threshold output from said tone bandpass filtering means.

Claim 8

In a radio receiver system of the type separably recovering first and second tonal modulation components on a received carrier; said receiver comprising means for amplitude detecting said tonal modulation components, tone bandpass filtering means receiving the output of said means of detecting and producing first and second output signals comprising said demodulated tones, means for rectifying the outputs from said bandpass filtering means and applying DC signals respectively proportional to the difference in amplitude of said tonal modulation components to an indicating means, and carrier frequency amplifying means receiving said carrier signal and including carrier frequency selective circuitry preceding any active element therein; a monitoring means for detecting malfunction in said receiver and annunciating same, said monitoring means comprising means for further amplitude modulating said received carrier frequency signal by varying the impedance of at least one of said carrier frequency selective circuits in accordance with a source of tracer signal having a predetermined frequency, means for controlling said tracer signal in frequency and phase at a frequency comprising substantially the mean of said first and second tonal modulation component frequencies and in a manner such that said tracer signal frequency component as coupled to said tone bandpass filtering means produces an equal effect upon the tone outputs from said tone bandpass filtering means, further bandpass filtering means centered about said tracer signal frequency receiving the output from said amplitude detecting means, means for phase detecting the output From said further bandpass filtering means with the output from said tracer signal source, and annunciating means responsive to a predetermined threshold output from said first phase detecting means to be activated.

Claim 9

In a radio receiver system of the type separably recovering first and second tonal modulation components on a received carrier; said receiver comprising means for amplitude detecting said tonal modulation components, tone bandpass filtering means receiving the output of said means of detecting and producing first and second output signals comprising said demodulated tones, means for rectifying the outputs from said bandpass filtering means and applying DC signals respectively proportional to the difference in amplitude of said tonal modulation components to an indicating means, and carrier frequency amplifying means receiving said carrier signal and including carrier frequency selective circuitry preceding any active element therein; a monitoring means for detecting malfunction in said receiver and annunciating same, said monitoring means comprising means for further amplitude modulating said received carrier frequency signal by varying the impedance of at least one of said carrier frequency selective circuits in accordance with a source of tracer signal having a predetermined frequency, means for controlling said tracer signal in frequency and phase at a frequency comprising substantially the mean of said first and second tonal modulation component frequencies and in a manner such that said tracer signal frequency component as coupled to said tone bandpass filtering means produces an equal effect upon the tone outputs from said tone bandpass filtering means, further bandpass filtering means centered about said tracer signal frequency receiving the output from said amplitude detecting means, means for phase detecting the output From said further bandpass filtering means with the output from said tracer signal source, and annunciating means responsive to a predetermined threshold output from said first phase detecting means to be activated.

Claim 10

A monitoring means as defined in claim 7 wherein said tone bandpass filtering means comprises first and second bandpass filtering means respectively responsive to an individual one of said first and second tonal modulation frequencies, each of said first and second bandpass filtering means exhibiting a predetermined like bandpass characteristic and being phase sensitive, and said means for controlling said tracer signal comprises means for phase locking said tracer signal source to a frequency to which said first and second bandpass filtering means are equally responsive.

Claim 11

A receiving system as defined in claim 8 wherein said means for phase locking comprises a still further bandpass filtering means connected to the outputs from said first and second bandpass filtering means and passing a signal the frequency of which is substantially equal that of the mean of said demodulated tone frequencies, a further phase detector receiving the output of said still further bandpass filtering means as a first input thereto, said tracer signal source comprising a second input to said further phase detector, low pass filtering means receiving the output of said further phase detector, and means for controlling the frequency of said tracer signal source as a function of the output from said low pass filtering means; and said annunciating means being connected to and additionally responsive to a predetermined threshold output from said low pass filtering means.