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This was a presentation given at the Radio Solutions Conference in London on 7th November 2001. The conference proceedings are available from the Low Power Radio Association.
Last updated 8th Nov 2001. Page hits since 8th Nov
2001
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Low frequency sub-surface radio is used for communications with miners and cavers. The signal attenuation is dependent on frequency and on the electrical conductivity of the ground. In addition, the optimum frequency for communications is dependent on depth below the surface; and on the degree of noise and co-channel interference. An adaptive communications system, under development now, makes use of a channel-sounding technique by transmitting a wideband signal and deriving the signal/noise ratio (SNR) as a function of frequency. The communications system can thereby alter its transmission frequency, and other parameters, to optimise SNR under different conditions. The same principles are relevant to applications in sub-surface radiolocation, archaeology and geophysics. The channel-sounding technique makes use of a modified pseudo-random binary sequence, which is cross-correlated with its inverse at the receiver, and which uses a code-locked loop to maintain synchronism with the transmitter. The transmitting antenna for such a system is essentially an induction loop, and the extreme wideband nature of the system requires this to be operated untuned. The resultant low efficiency is countered by using a suitable binary sequence at the transmitter and signal-averaging techniques at the receiver.
The above presentation included the following references. Click on the links to read the abstracts for these references. The papers by David Gibson (refs 1-5, 7 , 9) are available in a 'document bundle' from the author, which includes a copy of the above paper. (Please note that reference 9 will not be available until after the DSPCS 02 conference (ref 10), as a courtesy to the conference organisers).
The price of this document bundle is £20 (or £5 to BCRA personal members who do not represent commercial or academic bodies). You can pay by cheque, or order online and pay by credit card. (Please note that if you have a UK bank account it will be cheaper, and mucheasier for you to pay by cheque). Price includes postage world-wide. The documents are only available on paper at the moment - for PDFs please enquire. For further information about payment, or to order, click here.
1. Gibson, David (1994), Induction Radio for Communications Through Rock, Radio Solutions Conference Proceedings 1994, LPRA.
Induction radio is used for many applications; communications through rock to miners or potholers is one of the less well known, though it is by no means a new idea. The author has written several papers on theoretical aspects VLF radio for the Cave Radio & Electronics Group of the British Cave Research Association. This paper outlines the characteristics of induction radio. This is without a detailed mathematical analysis, though some equations are presented, and some knowledge of electronics and physics is assumed.
Although the principle of induction is straight-forward to understand there are a number of interesting aspects which come to light when the operation of a radio is analysed in detail; and the generation of near and far-fields is frequently misunderstood. Some aspects of the operation of induction radio systems are, at first sight, counter-intuitive. For example, the performance of the antenna does not depend on the number of turns of wire, but on the mass of the winding.
Some examples are given of the use and limitations of an induction radio system for communicating with cavers. Radio-location devices are also used in surveying caves and other civil engineering applications. The range is limited by the amount of wet, conductive, overburden and is very dependent on the mineralisation of the rock.
Induction radios are licence-exempt. Type approval is covered by MPT 1337 or BS 6083 (the unreleased MPT 1370). Devices operating below 9kHz may not need type-approval (except for EMC). Unfortunately MPT 1337 contains serious anomalies but its replacement, the draft ETS 300330 has been corrected.
2. Gibson, David (1997), Using Low Power Radio for Communicating through the Ground. Radio Solutions Conference Proceedings 1997, LPRA.
Commercial uses of low-frequency ground-penetrating radio include the tracking and telemetering of sondes in pipe-lines; voice-link systems for communicating with trapped miners; and the surveying of underground cavities in civil engineering applications. In addition to commercial uses, cavers and pot-holers have developed, largely on an amateur basis, a range of devices such as pagers, beacons, and systems for medical telemetry and video images. This presentation will describe, briefly, some commercial systems in use, and will outline the work being done on cave rescue systems.
3. Gibson, D. & M. Darnell (1999), Adaptive Digital Communications for Sub-Surface Radio Paths, Proc. DSPCS '99, pp237-244.
Low frequency sub-surface radio is used for communications with miners and cavers. The signal attenuation is dependent on frequency and on the electrical conductivity of the ground. In addition, the optimum frequency for communications is dependent on depth below the surface; and on the degree of noise and co-channel interference. An adaptive communications system makes use of a channel-sounding technique by transmitting a wideband signal and deriving the signal/noise ratio (SNR) as a function of frequency. The communications system can thereby alter its transmission frequency, and other parameters, to optimise SNR under different conditions. The same principles are relevant to applications in sub-surface radiolocation, archaeology and geophysics.
4. Gibson, David (1999), A Channel Sounder for Sub-Surface Communications: Part 1 - Adaptive Digital Communications for Sub-Surface Radio Paths, CREGJ 38, pp23-28, Dec 1999
Channel-sounders are used to test radio-wave propagation in a specified band, often the short-wave (HF) or one of the UHF 'cell-phone' bands. In this series of articles, David Gibson describes a new design of sounder that operates from 0 - 200kHz with a wide-band induction loop antenna. The sounder can also be used as a spectrum analyser, and is intended to be part of a wideband adaptive digital communications system.
Abstract for part 1: Low frequency sub-surface radio is used for communications with miners and cavers. The signal attenua-tion is dependent on frequency and on the electrical conductivity of the ground. In addition, the optimum frequency for commu-nications is dependent on depth below the surface; and on the degree of noise and co-channel interference. An adaptive communi-cations system makes use of a channel-sounding technique by transmitting a wide-band signal and deriving the signal/noise ratio (SNR) as a function of frequency. The communications system can thereby alter its transmission frequency, and other parame-ters, to optimise SNR under different condi-tions. The same principles are relevant to applications in sub-surface radiolocation, archaeology and geophysics.
5. Gibson, David (2000), A Channel Sounder for Sub-Surface Communications: Part 2 - Computer Simulation of a Small Buried Loop, CREGJ 41, pp29-32, Sept 2000
Channel-sounders are used to test radio-wave propagation in a specified band, often the short-wave (HF) or one of the UHF 'cell-phone' bands. In this series of articles, David Gibson describes a new design of sounder that operates from 0 - 200kHz with a wide-band induction loop antenna. The sounder can also be used as a spectrum analyser, and is intended to be part of a wideband adaptive digital communications system.
Abstract for part 2: The equations gov-erning the behaviour of a magnetic loop antenna and the field propagation were derived in the 1960s when computation was both slow and expensive. However, with powerful tools such as MatLab, iterations on a PC can now take seconds instead of hours. We can investigate field behaviour at a level of detail that was previously not possible. Such an analysis is of benefit both for the design of an adaptive communications system, and the investigation of new radio-location techniques. The results of the simulations will be tested in detail with the channel-sounder.
7. Gibson, David (1997), LF utility stations, CREGJ 28, pp16-17, June 97.
A list of transmitters operating in the LF spectrum, compiled by David Gibson from information supplied by Joerg Klingenfuss of Klingenfuss Publications, and others.
This table of LF utility stations has been complied from a list entitled "1996 Super Frequency List on CD-ROM", published by the German company Klingenfuss Publica-tions (see box). It is reproduced here by permission. Thanks are due also to John Hey and Nick Potter for the information about the Racal Decca navigation beacons.
9. Gibson, D. & M. Darnell (unpublished), A Channel Sounder for Low Frequency Sub-Surface Radio Paths.
In an application to measure subter-ranean radio propagation, a wide-band low-frequency channel sounder makes use of a modified pseudo-random binary sequence, which is cross-correlated with its inverse at the receiver, and which uses a code-locked loop to maintain synchronism with the transmitter. The transmitting antenna for such a system is essentially an induction loop, and the extreme wideband nature of the system requires this to be operated untuned. The resultant low efficiency is countered by using a suitable binary sequence at the transmitter and signal-averaging techniques at the receiver.