What is the HeyPhone?. The HeyPhone was designed by John Hey with the support of the British Cave Rescue Council BCRC and the Cave Radio & Electronics Group (CREG), which is a special interest group of the British Cave Research Association (BCRA). In the period up to 2001, working with CREG, the BCRC issued over fifty HeyPhones to the UK's cave rescue teams, allowing communication between the surface controller and one or more underground teams. This was the first time that a national organisation had systematically equipped its rescue teams with such advanced equipment. The impact of the HeyPhone on the UK cave rescue service was not due to any novel features of the HeyPhone - in fact, none are claimed - but to the dedication of John Hey and the CREG team that sought to bring the project to fruition by design, experimentation and documentation.

A key element of the project was to publish the design. The rescue groups saw this as an essential feature of the project and the availability of the documentation should ensure that HeyPhone users will be able to maintain their equipment and, perhaps, design and build compatible add-on equipment. Publishing the design also means that third parties will be able to build HeyPhones although neither the BCRC nor CREG undertakes to support third party construction. (It should be noted that those involved in the project have expressed the desire that the information should not be used for profit, and that the information on this web site is protected by copyright).

How does the HeyPhone work? Technically, the HeyPhone is a standard design of single-sideband radio, usually operating at 87kHz USB. In concept, it differs only marginally from Bob Mackin's Molefone, which was used by UK cave rescue groups in the 1970s. The Molefone operated using induction loops antennas and, whilst the HeyPhone can also do this, it is usually operated with earthed electrodes separated by 25m to 100m. This technique of current-injection into the earth re-creates the trench communications of the First World War, but the transmission range is enhanced by the use of the 87kHz carrier in the LF band.

Compared with induction loops, an earth-current system (which may also be referred to as an end-grounded horizontal electric dipole) offers a greater communications range for a lower power drain and with a less-critical alignment of the transmitter and receiver. (However, the radio licensing requirement of such a system has, in the past, been rather a grey area). A properly-designed induction-loop system could still have advantages over a less-mobile earth-current station, but the practical design of such systems still lags a long way behind the theoretical analysis.

Will there be any future developments? There is no doubt that the HeyPhone was welcomed by the rescue groups who were finding it increasingly difficult to maintain their ageing Molefones in working order. However, for a commercial application, considerable improvements could be made. The design contains a significant number of redundant components due, no doubt, to the speed of development and to the "committee" approach to the systems-engineering aspects. The design uses discrete logic for the control functions, for which the use of a microcontroller would bring about a significant reduction in component count. There are some aspects of the design - e.g. the phasing network and the receiver AGC - where more up-to-date designs would also be beneficial. There is also the point that the HeyPhone design, and its mode of operation, are "traditional", and can be further developed. For example, a DSP-based radio would significantly reduce the size, component count and cost. And why use SSB? Spread-spectrum is one possibility, and David Gibson has proposed a novel method utilising a quadrature phase space technique that might result in far less co-channel and adjacent-channel interference. Naturally, this additional level of development is difficult to achieve within a group of volunteers, working only in their spare time.

In 2006, Graham Naylor reported significant progress with his digital cave radio, which addresses some of the above points. For information on this and other cave radio projects, please see the CREG index to members' personal web pages.

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This page, http://bcra.org.uk/creg/heyphone/introduction.html was last modified on Sat, 14 Jan 2006 00:00:00 +0000
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