Data processing: measuring – calibrating – or testing – Calibration or correction system – Circuit tuning
Reexamination Certificate
1999-04-02
2001-10-16
Grimley, Arthur T. (Department: 2852)
Data processing: measuring, calibrating, or testing
Calibration or correction system
Circuit tuning
C702S106000, C702S190000, C702S191000, C702S193000, C702S195000, C342S090000, C342S162000, C455S212000, C340S315000, C375S317000
Reexamination Certificate
active
06304828
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to signal detection threshold circuits, and more particularly, relates to a system and method for automatically calibrating a signal detection threshold circuit.
(2) Description of the Prior Art
Signal detection threshold circuits are commonly used in receivers to prevent false signals from being detected by the receiver as a result of random noise. The signal detection threshold circuit determines whether the signals received are above a predetermined voltage or threshold setting. Only those signals of interest that exceed this threshold setting are passed on for detection by the receiver. Noise or other signals having an amplitude lower than the threshold setting are rejected by the signal detection threshold circuit.
Previously, technicians had to manually adjust receiver signal detection thresholds, and often the adjustment was made incorrectly. Setting the threshold too high caused a loss of sensitivity. In an early warning radar (EWR) system, for example, pulsed radio frequency (RF) signals will go undetected when the threshold is set too high. When the threshold is manually set too low, false signals are detected by the receiver due to random noise crossings.
This manual threshold alignment process was further complicated by the presence of signals in the environment. In some cases, radio frequency pre-amplifiers are remotely located from the receiver and outside signals cannot be isolated from the receiver detection circuits during calibration. This commonly occurs in military vessels and aircraft. In a submarine, for example, the pre-amplifier is often located in a periscope or an antenna mast close to the receiver antenna. Technicians must work around interfering signals to manually align signal detection thresholds in these systems. Manual alignment in such systems is time consuming and often results in an incorrect alignment and inadequate receiver performance.
SUMMARY OF THE INVENTION
One object of the present invention is to align signal detection thresholds in signal detection receivers to optimize receiver sensitivity for detection of pulsed RF signals, while limiting the false alarm rates due to random noise crossings.
Another object of the present invention is to automatically align signal detection thresholds in the presence of normally interfering signal environments.
A further object of the present invention is to quickly and accurately align the receiver signal detection threshold for the best achievable receiver performance and eliminate the possibility of operator error.
The present invention features a method of calibrating a signal detection threshold circuit comprising the steps of:
a. setting a threshold setting at an initial threshold value;
b. receiving noise signals in at least one signal channel in the signal detection threshold circuit;
c. rejecting each of the noise signals lower than the threshold setting;
d. determining a pulse repetition frequency (PRF) of noise pulses greater than the threshold setting;
e. lowering the threshold setting by a predetermined increment and repeating steps a-c until the pulse repetition frequency of the noise pulses is greater than a predetermined frequency;
f. storing the threshold setting as a noise measurement when the pulse repetition frequency is greater than the predetermined frequency;
g. repeating steps a-e until a predetermined number of noise measurements are made for the signal channel;
h. determining an average value of the predetermined number of noise measurements and setting the threshold setting to the average value when a predetermined number of acceptable noise measurements are made in the signal channel;
i. indicating successful calibration of the signal channel in the signal detection threshold circuit when a pre-determined number of acceptable noise measurements are made in the signal channel; and
j. indicating unsuccessful calibration of the signal channel in the signal detection threshold circuit when a predetermined number of unacceptable noise measurements are made in the signal channel.
The method preferably includes receiving noise signals in a plurality of signal channels, wherein steps a-j are performed for each of the plurality channel signals. The preferred method further includes repeating steps a-j for the signal channel if the predetermined number of acceptable noise measurements are not made in each signal channel. If the predetermined number of acceptable noise measurements are not made in the signal channel after repeating steps a-j for a predetermined number of times, the threshold setting is set to a default value.
According to one example, after the step of storing the threshold setting as the noise measurement, the method includes the steps of determining whether the noise measurement is greater than a predetermined maximum acceptable value or whether the noise measurement is less than a predetermined minimum acceptable threshold value. When the noise measurement is greater than the maximum acceptable value or less than the predetermined minimum acceptable value, the noise measurement is deemed an unsuccessful noise measurement. The method also includes the steps of providing an indication of excessive noise in the channel when the noise measurement is determined to be greater than the predetermined maximum acceptable value; and providing an indication of insufficient noise in the channel when the noise measurement is determined to be less than the predetermined minimum acceptable value.
The present invention also features an automatic signal detection threshold calibration system. The system comprises a plurality of signal channels for receiving and carrying a plurality of signals including noise signals. A threshold comparer is coupled to each of the signal channels for comparing the noise signals to a threshold setting and for rejecting each of the noise signals below the threshold setting. A detector is coupled to the threshold comparer for determining a pulse repetition frequency of each of the noise signals above the threshold setting. An automatic threshold determiner and setter is coupled to the detector for automatically determining the threshold setting by setting the threshold setting at an initial threshold value and lowering the threshold setting until the pulse repetition frequency of each of the noise signals above the threshold setting is greater than a predetermined frequency. A calibration indicator responsive to the automatic threshold determiner and setter provides an indication of a proper or improper calibration in each of the signal channels.
REFERENCES:
patent: 4005415 (1977-01-01), Kossiakoff et al.
patent: 4646254 (1987-02-01), O'Conner et al.
patent: 4648126 (1987-03-01), Toffolo
Huntley William P.
Swanick David J.
Charioui Mohamed
Gauthier Robert W.
Grimley Arthur T.
Lall Prithvi C.
McGowan Michael J.
LandOfFree
System and method for calibrating a signal detection... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with System and method for calibrating a signal detection..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System and method for calibrating a signal detection... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2616717