Advanced passive interference management in directional drilling system, apparatus and methods
A transmitter for inground use controls a depth signal transmit power in relation to a data signal transmit power such that one reception range of the depth signal at least approximately matches another, different reception range of the data signal. A portable device can form a system with the transmitter in which the portable device scans a plurality of frequencies within at least one low frequency depth signal range to measure the electromagnetic noise at each one of the plurality of frequencies and identify at least one of the frequencies as a potential depth frequency for the transmitter. The portable device can include a dual mode filter having a rebar mode and a normal mode filter. The depth signal frequency is dynamically positionable in relation to low frequency noise.
1. A portable device as part of a system in which a transmitter is configured to move through the ground in a region during an operational procedure while transmitting a depth signal at a depth frequency and a data stream at one or more data frequencies that at least characterizes an orientation parameter of the transmitter, said portable device comprising:
an antenna for receiving the depth signal and the data frequencies to produce an output;
a switchable filter section for limiting the antenna output in a normal mode to one frequency band that is above a predetermined frequency to pass the depth signal and the data stream at one or more frequencies and for limiting the antenna output in a rebar mode to another frequency band to pass the depth signal at less than the predetermined frequency and the data stream including the one or more frequencies above the predetermined frequency; and
a processor configured for switching the switchable filter section between the normal mode and the rebar mode to recover the depth signal and data stream responsive to selection of normal mode and the rebar mode.
2. The portable device of claim 1 wherein the switchable filter includes a normal mode filter for the normal mode and a rebar filter for the rebar mode.
3. The portable device of claim 1 wherein the predetermined frequency is 1 KHz.
4. The portable device of claim 1 wherein the rebar filter includes a rebar mode lower filter corner that is less than 1 KHz and the normal mode filter includes a normal mode lower filter corner that is greater than 1 KHz.
5. The portable device of claim 2 wherein the rebar filter defines a rebar passband that is wider in bandwidth than a normal mode passband that is defined by the normal mode filter.
6. The portable device of claim 5 wherein a first upper corner of the rebar passband at least approximately matches a second upper corner of the normal mode passband.
7. The portable device of claim 1 wherein said rebar band admits additional low frequency noise as compared to the normal mode band and wherein the portable device is further configured for scanning electromagnetic noise at least below said predetermined frequency to identify at least one low noise frequency for use by the transmitter as the rebar mode depth frequency in the rebar band to dynamically position the rebar mode frequency in relation to the additional low frequency noise.
8. The system of claim 1 wherein the portable device is configured for transmitting the identified low noise frequency to the transmitter to serve as the depth signal frequency.