System for locating concealed underground objects using digital filtering
AssigneeThe Charles Machine Works, Inc.
InventorsLloyd N. Salsman, Leslie D. Hoy
Life of this patent
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Abstract
A locating system has its performance enhanced by the use of digital filtering. The locating system may include a transmitter for transmitting an electromagnetic signal from a concealed object. The locating system may also use electromagnetic signals from existing electromagnetic sources unrelated to the locator system. A receiver is provided for receiving a selected electromagnetic signal. The signal is subsequently converted from an analog signal into a digital signal and subjected to digital filtering. The resulting digital signal is then processed to provide location information about the concealed object.
Claims27
A system for locating a concealed object comprising:
- transmitting means for transmitting an electromagnetic signal from said concealed object;
- and
- receiving and processing means for receiving and processing said electromagnetic signal, said receiving and processing means including
- antenna means for receiving said electromagnetic signal as an analog signal;
- amplifying means for amplifying said received analog signal;
- analog-to-digital converter means for converting said amplified analog signal to a digital signal, said analog-to-digital converter means sampling said amplified analog signal at a predetermined frequency;
- digital filter means for filtering said digital signal, said digital filter means including a two-stage digital filter, the filter characteristics of said first stage of said two-stage digital filter being defined by parameters AO11 and AO12, and the filter characteristics of said second stage of said two-stage digital filter being defined by parameters AO21 and AO22, wherein
- AOx1=2*(1-1/q) *cos (2*pi*fctr/fsmpl)*16384
- and
- AOx2=-(1-1/q).sup.2 *32768,
- wherein
- q=quality factor,
- fctr=center frequency,
- fsmpl=sampling frequency, and
- x=1 or 2;
- and
- processing means for processing said filtered digital signal to provide an output signal indicative of the location of said concealed object.
A method of selecting a two-stage digital filter for use in a locating system including means for receiving a signal radiated from a concealed object as an analog signal, means for amplifying the received analog signal, means for converting the amplified analog signal to a digital signal, and a two-stage digital filter for filtering said digital signal, the means for converting said amplified analog signal to a digital signal sampling the amplified analog signal at a predetermined frequency, wherein the characteristics of said two-stage digital filter are defined by coefficients AO11, AO12, AO21 and AO22, the method comprising:
- calculating said coefficients AO11, AO12, AO21 and AO22 according to the following formulae:
- AOx1=2*(1-1/q) *cos (2*pi*fctr/fsmpl)*16384
- and
- AOx2=-(1-1/q).sup.2 *32768
- wherein
- q=quality factor
- fctr=center frequency
- fsmpl=sampling frequency, and
- x=1 or 2;
- and
- performing a stabilization analysis of the digital filter defined by said coefficients.
A receiver for receiving an electromagnetic signal radiated by a concealed object to indicate the location of said concealed object comprising:
- a. antenna means for receiving said electromagnetic signal as an analog signal;
- b. amplifying means for amplifying said analog signal;
- c. analog-to-digital converter means for converting said amplified analog signal to a digital signal, said analog-to-digital converter means sampling said amplified analog signal at a predetermined frequency;
- d. digital filter means for filtering said digital signal, said digital filter means including a two-stage digital filter, the filter characteristics of the first stage of said two-stage digital filter being defined by parameters AO11 and AO12, and the filter characteristics of the second stage of said two-stage digital filter being defined by parameters AO21 and AO22 wherein
- AOx1=2*(1-1/q) *cos (2*pi*fctr/fsmpl)*16384
- and
- AOx2=-(1-1/q).sup.2 *32768,
- wherein
- q=quality factor,
- fctr=center frequency,
- fsmpl=sampling frequency, and
- x=1 or 2;
- and
- e. processing means for processing said filtered digital signal to indicate the location of said concealed object.
Dependencies are inferred from the claim text.