Method and apparatus for frequency stabilization of a down converter

• US 5,046,135 A
• Filed: 11/30/1989
• Issued: 09/03/1991
• Est. Priority Date: 11/30/1989
• Status: Expired due to Term

• Current Assignee: John E Chance & Associates
• Original Assignee: John E Chance & Associates
• Inventors: Hatcher, G. Stephen
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): CHAROUEL, LISA
• Application Number:
  US07/443,145
• Time in Patent Office: 642 Days
• Field of Search: 455/214, 455/302, 455/303, 455/314, 455/315, 455/317, 455/319, 455/316, 342/357, 342/358, 342/395, 342/400, 342/420, 364/427
• US Class Current: 455/303
• CPC Class Codes: H04B 1/26 for superheterodyne receivers multiple frequency-changing H03D7/16

Abstract

A method and apparatus is disclosed for automatic elimination of frequency instabilities in a receiver frequency converter. Such instabilities result from temperature variations and mechanical vibrations of the local oscillator of a first stage converter. A marker signal is introduced into the first stage down converter mixer and is subjected to the same variations in frequency conversion as is the received signal from an antenna. Intermediate down converted received signals and an intermediate down converted marker signal are received by a second stage converter where such signals are applied to a mixer, the output of which is free of frequency variations introduced by the local oscillator of the first stage converter.

Claims

1. A receiver for converting a high frequency received signal including a band of signal frequencies to a lower band of signal frequencies comprising:

a first local oscillator which produces a first oscillator signal of a first oscillator frequency, said first oscillator frequency varying in frequency by an error frequency;

means for generating a marker signal having a marker frequency;

mixer means which is;

(a) responsive to said received signal and said first oscillator signal for generating a first intermediate band of signal frequencies superimposed thereon, and

(b) responsive to said marker signal and said first oscillator signal for generating a first intermediate marker signal of a first intermediate marker frequency;

base band mixer means responsive to a signal including said first intermediate signal band and to a signal including said first intermediate marker signal for intermediate marker signal for generating a base band signal, said base band signal having a frequency band definition which includes the difference between said frequency band of said received signal and said marker frequency of said marker signal, wherein said base band signal is substantially free of said error frequency of said first oscillator frequency, and

wherein said first intermediate band of signal frequencies and said first intermediate marker signal are generated on a single cable,

said receiver further comprising,

diplexer means for separating said signals on said single cable such that said first intermediate signal band is applied to a first signal path and said first intermediate marker signal is applied to a second signal path,

a second local oscillator which produces a second oscillator signal of a second oscillator frequency,

second mixer means which is responsive to said first intermediate signal band on said first signal path and to said second oscillator signal for generating a second intermediate signal band of frequencies superimposed thereon,

a third local oscillator which produces a third oscillator signal of a third oscillator frequency,

third mixer means which is responsive to said intermediate marker signal and to said third oscillator signal for generating a second intermediate marker signal of a second intermediate marker frequency, and

wherein said second intermediate signal band and said second intermediate marker signal are applied to said base band mixer means for generating said base band signal having a frequency definition which includes the difference between said frequency of said frequency band of said received signal and said marker frequency of said marker signal and in addition said base band signal frequency definition includes the difference between said frequency of said second oscillator signal and said frequency of said third oscillator signal.

2. The receiver of claim 1 wherein said high frequency received signal is generated on an antenna which is located at a remote distance from said diplexer means,

said high frequency received signal is in the 3.7-4.2 GHz band, and

said first local oscillator generates a first oscillator frequency of 5150 MHz and is disposed at a location subjecting its frequency output to frequency drift due to temperature variations and/or mechanical vibration.

3. The receiver of claim 2 wherein said first intermediate band of signal frequencies is from 950 to 1450 MHz.

4. The receiver of claim 3 wherein said marker frequency of said marker signal is 4228 MHz which when mixed with said first oscillator frequency produces a first intermediate marker frequency of 922 MHz.

5. The receiver of claim 1 wherein said diplexer means responsive to signals on said single cable includes

a high pass filter for passing to said first signal path said intermediate band of signal frequencies while blocking said first intermediate marker frequency, and

a low pass filter for blocking said intermediate band of signal frequencies while passing said first intermediate marker frequency to said second signal path.

6. The receiver of claim 5 wherein said first intermediate marker frequency is less than frequencies of said first intermediate band of signal frequencies.

7. The receiver of claim 1 wherein

said high frequency received signal is generated on an antenna which is located at a remote distance from a location at which said diplexer means is disposed,

said first local oscillator and said mixer means being disposed at a location subjecting the frequency of said first local oscillator to frequency drift due to temperature and/or mechanical vibrations, said location of said first local oscillator and said mixer means being relatively nearer said antenna than said diplexer means so as to produce a band of signals in an intermediate frequency range in order to reduce attenuation of signals via said single cable to said diplexer means,

said means for generating a marker signal including,

a marker oscillator disposed at a location at which said diplexer means is disposed,

said marker oscillator generating a local oscillator signal of an intermediate frequency, and

means for transmitting said local oscillator signal and multiplying the frequency of said local oscillator signal at said local oscillator signal at said location of said first local oscillator and said mixer means to produce said marker signal of said marker frequency and applying same to said mixer means.

8. The receiver of claim 7 wherein

said marker oscillator generates a local oscillator signal at an intermediate frequency of 528.5 MHz.

9. The receiver of claim 7 wherein said means for transmitting and multiplying the frequency of said local oscillator signal comprises,

a first directional coupler means disposed at a location at which said diplexer means is disposed and associated with said single cable for accepting said local oscillator signal and directing same toward said mixer means via said single cable yet blocking transmission of said local oscillator signal via said single cable toward said diplexer means,

a second directional coupler means disposed at a location at which said mixer means is disposed and associated with said single cable for accepting said local oscillator signal and directing same toward a marker multiplier loop means yet blocking transmission of said local oscillator signal via said single cable toward said mixer means,

said marker multiplier loop means responsive to said local oscillator signal via said single cable for multiplying the frequency of said local oscillator signal to produce said marker signal, and

a third directional coupler means disposed at a location at where said mixer means is disposed and associated with a receiving cable by which said high frequency received signal is applied to said mixer means for accepting said marker signal and directing same toward said mixer means via said receiving cable yet blocking transmission of said marker signal via said receiving cable away from said mixer means.

10. In a receiver system in which an antenna and a first frequency conversion stage is disposed at a first location subject to variations in temperature and mechanical vibration and in which a second frequency conversion stage is disposed at a second location not substantially subject to variations in temperature and mechanical vibration, wherein said first and second frequency conversion stages are interconnected by a cable, a method for substantially eliminating frequency shift errors introduced into the receiver system due to temperature variations and mechanical vibrations at said first frequency conversion stage comprising the steps of,

introducing a marker signal of marker frequency into a mixer of said first frequency conversion stage so that said marker frequency is converted to an intermediate marker signal of an intermediate marker frequency by the same frequency of a first stage local oscillator as is the band of frequencies of a received signal from said antenna is converted to an intermediate received signal of intermediate band of signal frequencies,

receiving said intermediate marker signal and said intermediate received signal at said second frequency conversion stage via said cable,

separating said intermediate received signal and said intermediate marker signal onto respective first and second processing paths,

applying said intermediate received signal and said intermediate marker signal to a mixer to produce a base band signal having a frequency band definition which includes the difference between said frequency band of said received signal and said marker frequency of said marker signal, wherein said base band signal is substantially free of said error frequency of said first stage local oscillator frequency.

11. In a receiver system in which an antenna and a local oscillator and mixer of a first frequency conversion stage is disposed at a first location which is subject to variations in temperature and mechanical vibration and in which a second frequency conversion stage is disposed at a second location, with said first and second frequency stages interconnected by a cable, apparatus for substantially eliminating frequency shift errors introduced into the receiver system due to temperature variations and mechanical vibrations effects of said local oscillator of the first frequency conversion stage comprising,

means for converting a high frequency information signal received from said antenna to an intermediate frequency information signal by mixing said high frequency information signal with a signal of said local oscillator of said first conversion stage and applying said intermediate frequency information signal to said cable, said signal of said local oscillator having a nominal frequency which varies by an error frequency;

means for applying a marker signal to said first frequency conversion stage at said first location where said marker signal is modulated in said mixer by said frequency of said local oscillator and applying to said cable at said first location a first intermediate marker signal of a first intermediate marker frequency, where said local oscillator frequency is said nominal frequency which varies in frequency by said error frequency, and

base band mixer circuit means connected to said cable at said second location which is responsive to said first intermediate marker signal and to said first intermediate information signal for generating a base band information signal which is substantially free of said error frequency of said local oscillator at said first location.

12. The apparatus of claim 11 wherein said base band mixer circuit means includes,

means for separating said first intermediate information signal and said first intermediate marker signal onto respective first and second processing paths, and

means for applying said first intermediate information signal and said intermediate information marker signal to a mixer to produce said base band information signal having a frequency band definition which includes the difference between said frequency band of said information signal and said marker frequency.