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# format auto-updated on access: Mon 27-Nov-2017 11:29:52 +01:00 CREG Journal Contents. (This is a bit-map scan). The GB2CRO - GB4CRO Link-up Mike Bedford reports on the recent HF link-up between underground stations operating from the Yorkshire Dales and South Wales. Talk-through Boxes A 'talk-through box' is the correct terminology for the type of 'repeater' needed to interface a cave radio to devices such as HF radios, telephones and so on. Mike Bedford and David Gibson explain the principles. Induction Radio or Telephone? Stuart France uses his experience with South Wales CRO to contrast the Ogofone with cable-laid telephones. Eavesdropping on Bats Dave Whiteley gives some background on bats and how to listen to them electronically. 49MHz Radios Underground Pete Allwright describes the use of 49MHz hands-free radios by the CRO in the Yorkshire Dales. Update - The France/Mackin Radio-location Beacon Mike Bedford gives further information about the tuning capacitors used in the France/Mackin beacon. Simplex Protocols for Cave Radios In a glossary and draft specification, David Gibson discusses the operation of a PTT switch, cueing tones, hands-free operation, and talk-through boxes. PICs for Cave Radio Control Mike Bedford describes how a small PIC microcontroller can be used in a cave radio application; in this case, for a cueing tone generator. High Power Switching Regulator David Gibson introduces a novel design. Earth Current / Induction Field Experiments - part 2 Rob Gill reports on further experiments. Earth Rod Resistivity 20 Rib Gill compares a hexagonal array with a single long rod. Sodium Lamps for Caving Nick Williams and David Gibson describe the characteristics of these lamps. Update - An Ergonomic Loop Antenna Mike Bedford updates his earlier design. Signal/Noise Ratio - Part 1 of a Series on Receiver Noise Topics David Gibson introduces this series and explains the steps leading up to an expression for the s/n ratio of an induction loop receiver. Cave Radio Notebook David Gibson's notes on 4: earth current communication, 5: circular polarisation, 5: [sic] ground conductivity. Wet & Dry Our regular(ish) column on waterproof electronics. More on waterproof speakers by David Gibson.