# US 10,310,130 B2 · Cable detection apparatus with a comb filter

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- Number: US 10,310,130 B2
- Document ID: US10310130B2
- Status: Granted
- Kind: B2
- Application number: 14/625,496
- Filed: 2015-02-18
- Published: 2015-08-20
- Granted: 2019-06-04
- Earliest claimed: 2014-02-19
- Assignees: Metrotech Corporation
- Applicants: Metrotech Corporation
- Inventors: Johan Overby; John Mark Royle
- Web page: https://patentgrep.com/patent/US10310130B2

## CPC

- G01V 3/10: using induction coils
- G01V 3/12: operating with electromagnetic waves {(operating with millimetre waves G01V8/005)}
- G01V 13/00: Manufacturing, calibrating, cleaning, or repairing instruments or devices covered by groups G01V1/00 – G01V11/00
- G01V: GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS (means for indicating the location of accidentally buried, e.g. snow-buried, persons A63B29/02)

## Abstract

An apparatus that uses harmonics of the power line frequency at which electrical power is distributed is presented. The apparatus includes a sensor antenna to detect an electromagnetic field produced by a cable. The output of the sensor is fed to a mixer together with a signal from a sine wave generator at less than the fundamental power frequency to frequency shift the signals from the sensor. The mixed output is then amplified to provide an audible output. A single comb filter receives signals from the mixer and outputs a filtered signal removing non-harmonic frequencies but preferably passing both odd and even harmonics. The output of the comb filter is then integrated at and displayed to indicate the detection of a cable based on the filtered signal.

## Claims

### Claim 1

A cable detection apparatus comprising:
a sensor to detect an electromagnetic field produced by a cable and provide signals, the electromagnetic field expected to have a component at a first frequency;
a frequency shifter to frequency shift the signals from the sensor by a second frequency of half the first frequency;
an amplifier that receives the frequency shifted signals;
a first filter to receive signals from the amplifier and output a filtered signal, the first filter having a higher transmittance at the second frequency and at the second frequency shifted by whole multiples of the first frequency than at least one frequency between two of said shifted frequencies; and
an indicator to indicate the detection of the cable based on the filtered signal.

### Claim 2 (depends on 1)

The cable detection apparatus of claim 1, wherein the whole multiples include both odd and even multiples.

### Claim 3 (depends on 1)

The cable detection apparatus of claim 1, wherein there is only a single comb filter between the sensor and the indicator.

### Claim 4 (depends on 1)

The cable detection apparatus of claim 1, wherein the first filter is a comb filter.

### Claim 5 (depends on 1)

The cable detection apparatus of claim 1, wherein the frequency shifter includes a mixer and a sine wave generator operating at the second frequency.

### Claim 6 (depends on 1)

The cable detection apparatus of claim 1, further comprising a second filter between the amplifier and the first filter, the second filter being a high-pass filter to remove a B-field of the earth from the signals received from the amplifier.

### Claim 7

A method of cable detection, the method comprising:
sensing an electromagnetic field produced by a cable to provide signals, the electromagnetic field expected to have a component at a first frequency;
frequency shifting the signals by a second frequency of half the first frequency;
amplifying the frequency shifted signals;
filtering, using a first filter, the amplified signals, the first filter having a higher transmittance at the second frequency and at the second frequency shifted by whole multiples of the first frequency than at least one frequency between two of said shifted frequencies; and
indicating detection of the cable based on the filtering.

### Claim 8 (depends on 7)

The method of claim 7, wherein the whole multiples include both odd and even multiples.

### Claim 9 (depends on 7)

The method of claim 7, further comprising filtering using only a single comb filter.

### Claim 10 (depends on 7)

The method of claim 7, wherein the first filter is a comb filter.

### Claim 11 (depends on 7)

The method of claim 7, wherein the frequency shifting includes mixing in a sine wave having the second frequency.

### Claim 12 (depends on 7)

The method of claim 7, further comprising filtering, using a high-pass filter, the amplified signals to remove a B-field of the earth from the amplified signals.