METHOD AND APPARATUS FOR MEASURING MULTIPATH DISTORTION

• US 3,869,673 A
• Filed: 05/21/1973
• Issued: 03/04/1975
• Est. Priority Date: 05/21/1973
• Status: Expired due to Term

• Current Assignee: Ernest Frederick Close
• Original Assignee: Ernest Frederick Close
• Inventors: Close, Ernest Frederick
• Primary Examiner(s): Libman, George H.
• Application Number:
  US05/361,902
• Time in Patent Office: 652 Days
• Field of Search: 325/67,65,363,398,473,455 328/163
• US Class Current: 455/210
• CPC Class Codes: G01R 29/0814 Field measurements related to measuring influence on or from apparatus, components or humans EMC, EMI and similar testing in general G01R31/001, e.g. in ESD, EMI, EMC, EMP testing, measuring radiation leakage; detecting presence of micro- or radiowave emitters; dosimetry; testing shielding; measurements related to lightning
• CPC Class Codes: H04B 17/364 Delay profiles

Abstract

A quantitative approximation of the distortion due to multipath reception of a frequency modulated or other angle modulated signal is obtained by detecting the frequency variations in the received signal and providing a first output signal, such as the discriminator output, indicative of those frequency variations and additionally detecting the amplitude variations in that same signal and providing a second output signal indicative of those amplitude variations. The first and second output signals are then correlated, with the degree of correlation providing a quantitative measure of the multipath distortion present in the received signal. In a first embodiment, the correlation is obtained using a doubly balanced mixer or multiplier circuit while in a second embodiment this correlation is approximated by the use of a single balanced mixer.

Claims

1. In an FM receiver having a sequentially coupled radio frequency amplifier, mixer, intermediate frequency amplifier, limiter, frequency modulation detector and audio output stages;

a circuit for providing a quantitative measure of the distortion present in a received signal due to propagation of that signal along paths of dissimilar lengths comprising;

an amplitude modulation detector having an input coupled to the receiver prior to the limiter and having an output;

multiple input amplifier means for providing an output signal the magnitude of which varies directly as a function of the magnitude of each input signal;

means coupling the output of the amplitude modulation detector to at least one of the amplifier means multiple inputs;

means coupling the output of the frequency modulation detector to at least another of the amplifier means multiple inputs;

indicator means coupled to the output of said amplifier means output to indicate the quantitative measure of said distortion present in a received signal; and

wherein the amplifier means comprises a multiplier circuit for forming the instantaneous product of the signals presented to the multiple inputs.

2. The circuit of claim 1 further comprising rectifying means in circuit with at least one of said coupling means to thereby present a unidirectional likeness of the corresponding at least one signal to the corresponding multiple inputs.

3. The circuit of claim 1 wherein said indicator means comprises a panel display meter coupled to the said amplifier means and responsive to the output thereof to provide a visible deflection corresponding to the quantitative measure of distortion present in the received signal.

4. The circuit of claim 3 further comprising a capacitor in parallel with the said panel display meter to stabilize the indication provided by that meter and provide an indication of average distortion present in the received signal.

5. The circuit of claim 4 further comprising rectifying means coupling the amplifier means and the parallel combination of the capacitor and panel display meter to thereby supply a unidirectional likeness of the output of the amplifier means to the said parallel combination.

6. The method of obtaining a quantitative approximation of the distortion due to multipath reception of a frequency modulated signal comprising the steps of:

detecting the frequency variations in a received signal and providing a first output signal indicative of those frequency variations;

detecting the amplitude variations in that same received signal and providing a second output signal indicative of those amplitude variations;

correlating the first and second output signals;

providing an indication of the degree of correlation between the first and second output signals; and

wherein the step of correlating includes the steps of providing a unidirectional likeness of the first output signal, providing a unidirectional likeness of the second output signal, and providing the instantaneous product of the two thus provided likenesses.

7. The method of claim 6 further comprising the step of averaging the instantaneous product to thereby provide an indication of average distortion in the received signal.

8. The method of obtaining a quantitative approximation of the distortion due to multipath reception of a frequency modulated signal comprising the steps of:

detecting the frequency variations in a received signal and providing a first output signal indicative of those frequency variations;

detectiNg the amplitude variations in that same received signal and providing a second output signal indicative of those amplitude variations;

correlating the first and second output signals;

providing an indication of the degree of correlation between the first and second output signals; and

wherein the step of correlating includes the step of providing an instantaneous product of the first and second output signals, and providing a unidirectional likeness of the thus provided product.

9. In a receiver for receiving angle modulated signals, a circuit for providing a measure of the distortion present between such received signals due to multipath reception of those signals comprising:

means for angle demodulating the received signals;

means for amplitude demodulating the received signals; and

means coupled to each said demodulating means and responsive thereto to provide an indication of the correlation between angle modulation and amplitude modulation in received signals; and

wherein the coupled means comprises a multiplier circuit for forming the instantaneous product of signals presented thereto, and rectifier means coupling the multiplier circuit to each said demodulating means to thereby form the product of unidirectional likenesses of the respective demodulated signals.

10. The circuit of claim 9 further comprising a panel display meter coupled to the said multiplier circuit and responsive to the output thereof for providing a visible deflection which indicates a measure of the distortion present in the received signals.

11. The circuit of claim 10 further comprising a capacitor in parallel with the panel display meter to stabilize the meter indication and provide an indication of the average value of the multiplier circuit output.

12. In a receiver for receiving angle modulated signals, a circuit for providing a measure of the distortion present between such received signals due to multipath reception of those signals comprising:

means for angle demodulating the received signals;

means for amplitude demodulating the received signals; and

means coupled to each said demodulating means and responsive thereto to provide an indication of the correlation between angle modulation and amplitude modulation in received signals; and

wherein the coupled means comprises means for forming the instantaneous product of the signals presented thereto, a panel display meter, and rectifier means coupling the coupled means to the panel display meter to thereby display an indication of the magnitude of a unidirectional likeness of the instantaneous product of the two signals presented to the coupled means.