FREQUENCY BAND SHIFTER

• US 3,691,394 A
• Filed: 08/25/1971
• Issued: 09/12/1972
• Est. Priority Date: 08/25/1971
• Status: Expired due to Term

• Current Assignee: Scientific-Atlanta Incorporated (Cisco Systems, Inc.)
• Original Assignee: Robert B. Davis
• Inventors: Davis, Robert D.
• Primary Examiner(s): Schaefer, Robert K.
• Assistant Examiner(s): Smith, William J.
• Application Number:
  US05/174,672
• Time in Patent Office: 384 Days
• Field of Search: 307/3,13 332/16 328/15 331/47,179,30
• US Class Current: 307/3
• CPC Class Codes: G01R 23/00 Arrangements for measuring frequencies; Arrangements for analysing frequency spectra

Abstract

A frequency band shifter for shifting a selected frequency band in a complex waveform, which frequency band is translated with its relative frequency, phase and amplitude relationships maintained to a reproduced lower frequency and, if desired, to a smaller frequency band for analysis, which translation is processed by manual or digital control with a master local oscillator control clock that provides protection against drift in frequency and phase throughout the system.

Claims

1. In a frequency band shifter for shifting a selected bandwidth of frequencies of a complex signal, means for providing a reference signal having a given frequency, means for providing a second signal having a frequency corresponding to selected center frequency of a particular bandwidth of frequencies in the complex signal, means for summing the reference signal with said second signal and producing a carrier signal, data modulator means for modulating said carrier signal with the complex signal producing translated signals, means for polyphase modulating the translated signals with the reference signal producing an output signal band having the center frequency of the reference signal and the amplitude and phase of the frequency band of interest in the complex signal, means for providing a demodulating carrier signal having a frequency slightly greater than said reference signal, and data demodulator and filter means for modulat1ng said demodulating carrier signal with said output signal band and filtering the demodulated output producing a bandwidth of frequencies having a center frequency corresponding to the frequency difference between said reference signal and said demodulating carrier signal.

2. In a frequency band shifter as claimed in claim 1, including, a master oscillator for providing a master output frequency signal, and means for locking the phase of said reference signal, said second signal and said programmed low frequency signal to said master frequency signal.

3. In a frequency band shifter as claimed in claim 1 in which, said polyphase modulating means includes demodulator means for translating said translated signals down to audio range, phase and amplitude coherent bandpass filter means for filtering said translated signals, and modulator means for translating said filter signals to the frequency of the reference signal.

4. In a frequency band shifter as claimed in claim 3 in which, said bandpass filter means comprises zero IF variable bandwidth and bandpass filters, and means for providing a signal that selectively sets the frequency range of the bandwidth of said bandpass filters.

5. In a frequency band shifter as claimed in claim 4 including, means for providing a programmed signal determinative of the selective bandwidth of the complex signal translated, and said zero IF bandpass filters being responsive to said signal for setting the bandwidth of said filters.

6. In a frequency band shifter as claimed in claim 1 in which, said polyphase modulating means having first and second circuit channels, each of said circuit channels having phase and amplitude coherent bandpass filter sections, and means for supplying a bandpass controlling signal to said bandpass filter sections for controlling the bandwidth of said bandpass filter sections.

7. In a frequency band shifter as claimed in claim 1 in which, said polyphase modulating means comprising first and second circuit channels, each of said channels having a demodulator for receiving the translated signals, connected in series with a variable bandwidth and bandpass low pass filter connected in series with a modulator, means for supplying said reference frequency to each of the demodulators and modulators in the first channel and supplying the reference frequency with a 90* phase shift to the demodulators and modulators in the second channel, and summing means for summing the output signals from the modulators in Each of the channels.

8. In a frequency band shifter as claimed in claim 7 including, means for providing a programmed signal to each of said variable bandwidth and bandpass filters, and said variable bandwidth and bandpass filters having their pass-band set by said programmed input signal.

9. In a frequency band shifter as claimed in claim 1 including, encoder means for providing an output signal corresponding to a selected frequency signal, phase lock multiplier means responsive to said master output frequency signal and said signal from said encoder for providing said second signal that is phase locked to said master output frequency signal, and said summing means for summing the reference signal to said second signal having means for phase locking said carrier signal to said master output frequency signal.

10. In a frequency band shifter as claimed in claim 9 including, bandwidth switching means responsive to said master output frequency signal and input control signals for providing said demodulator carrier signal which demodulating carrier signals are phase locked to said master output frequency signal.

11. The method of translating a selected bandwidth of frequencies of a complex signal to a lower frequency band while preserving phase and amplitude coherence comprising the steps of, modulating the complex signal with a signal comprising a reference frequency plus a second frequency corresponding to the center frequency of the selected bandwidth of the complex signal to be translated, passing the modulated output through a phase and amplitude coherent bandpass filter section that employs polyphase modulation to translate the modulated output down to the audio range, and raising the filtered output to the frequency of the lower frequency band to which the selected band width of frequencies of the complex signal is being translated.

12. The method of claim 11 including the step of, selectively varying the bandwidth of the bandpass filter section to selectively vary the bandwidth of frequencies of the complex signal that are translated.

13. In the method of claim 12 including the step of, selectively setting the center frequency of the lower frequency band to which the selected bandwidth of frequencies of the complex signal are translated to a frequency that in conjunction with the selected bandwidth of the bandpass filter section, maintains the lower frequency band above zero frequency.

14. In the method of claim 13 including the step of, phase locking the reference signal and the second frequency and the center frequency signal of the lower frequency translated band to the phase of a master oscillator output.

15. In the method defined in claim 14 including the step of, modulating the output of the bandpass filter section with said reference frequency, demodulating said modulated output with a signal comprising said reference frequency and the selected center frequency of the lower frequency translated band, and filtering the demodulated output to the lower frequency translated band.

16. In the method claimed in claim 14 including the step of, controlling the center frequency the lower frequency translated band by computer program command.