Radio frequency digital fourier analyzer

• US 3,876,946 A
• Filed: 10/31/1973
• Issued: 04/08/1975
• Est. Priority Date: 10/31/1973
• Status: Expired due to Term

• Current Assignee: Librascope Corporation
• Original Assignee: Gunther W. Sorger, John P Mccarthy, Philip W. La Clair
• Inventors: La Clair, Philip W., McCarthy, John P., Sorger, Gunther W.
• Primary Examiner(s): Morrison, Malcolm A.
• Assistant Examiner(s): Malzahn, David H.
• Application Number:
  US05/411,502
• Time in Patent Office: 524 Days
• Field of Search: 325/363,67 324/77C,77CS 235/152
• US Class Current: 702/77
• CPC Class Codes: G01R 23/18 with provision for recording frequency spectrum

Abstract

A radio frequency digital Fourier analyzer is provided which serves not only as a spectrum analyzer, but as an important statistical tool. The digital Fourier analyzer comprises a twochannel receiver which is interfaced with a digital computer through an analog/digital converter, and which also includes appropriate control, peripheral and read-out equipment. The receiver comprises a two-channel radio frequency/intermediate frequency converter, and it can operate as an analog spectrum anaylzer or network analyzer. The receiver responds to radio frequency signals in a frequency range of, for example, 500 KHz to 1,300 MHz. The receiver converts a radio frequency signal which is to be analyzed into a band-limited intermediate frequency signal of the proper frequency for digital conversion. The analog/digital converter converts the intermediate frequency signal from the receiver into digital data for the computer. The computer calculates the fast Fourier transform (FFT) of the sampled data and uses the result to calculate one or more desired functions. The read-out equipment displays and/or records the results of the computation.

Claims

1. A radio frequency digital Fourier analyzer system comprising:

a pair of input circuits for receiving a pair of separate signals each lying in a predetermined radio frequency range;

a radio frequency/intermediate frequency converter circuit coupled to each of said pair of input circuits and responsive to said radio frequency signals to produce intermediate frequency output signals of a particular intermediate frequency and bandwidth;

an analog/digital converter coupled to the outputs of said radio frequency/intermediate frequency converter circuits for transforming each intermediate frequency output signal into a corresponding digital signal;

digital computer means coupled to said analog/digital converter and responsive to the digital signal therefrom for performing computations corresponding to selected Fourier transforms; and

readout means coupled to said digital computer means for utilizing output information from the computer means corresponding to the aforesaid computations.

2. The radio frequency digital Fourier analyzer defined in claim 1, in which each of said radio frequency/intermediate frequency converter circuits includes at least one mixer coupled to a variable frequency local oscillator for heterodyning a received radio frequency signal to a selected intermediate frequency said local oscillator being coupled to permit said computer means to control the frequency of said local oscillator in discrete steps through a predetermined frequency range.

3. The radio frequency digital Fourier analyzer defined in claim 1, in which each of said radio frequency/intermediate frequency converter circuits includes an automatic gain control circuit responsive to the output signal level of one of said converter circuits and to said digital computer means for maintaining a predetermined amplitude of the intermediate frequency output signals of each of said converter circuits at a maximum value with respect to the requirements of said analog/digital converter.

4. The radio frequency digital Fourier analyzer system defined in claim 1, in which each of said radio frequency/intermediate frequency converter circuits includes a plurality of bandpass filters, and further includes switching means connected to said plurality for selectively coupling one of said plurality in series with the output of said converter circuit, so as to establish different bandwidths of said intermediate frequency output signal.