sandbox: Journal 130 has gone to press and is due for publication in June 2025
CREG Journal 130 (0-24)
This issue has a cover date of June 2025 and was published on 1 June 2025.

Front Cover (1)
Electrical conductivity measurement being taken in Dr&#x10D;a Jama, Slovenia. Photo: <span class="author">Alexander Debenjak</span> - J. K. Kra&scaron;ki Krti

Contents (2)
List of contents and masthead information.

News and Notes (2)
Field Meeting Postponed, Editorial Team, Hidden Earth.

A Cheap Portable Electrical Conductivity and pH Meter for Identifying Underground Waters (3-7)
In the Classical Karst area, the numerous surface and underground springs get their water from three rivers, which always present electrical conductivity (EC) values that are different from each other, especially during high flow. So, the source of water can be determined by measuring the EC during the same period each Spring. This requires many conductivity meters, which are expensive. As <span class="author">Luca Tringali</span>, <span class="author">Matteo Cavanna</span>, <span class="author">Alexander Debenjak</span>, <span class="author">Tecla Tripari</span>, <span class="author">Max Stabile</span>, <span class="author">Caterina Bearzotti</span> and <span class="author">Giacomo Canciani</span> report, a cheap EC meter that they developed, while less precise than commercial ones, is suitable for detecting Classical Karst waters.

We Hear (8)
<span class="author">Mike Bedford</span> reports: UK to get Commercial eLORAN Service, Monitoring Radon in Poole's Cavern, Raspberry Pi Launch Bare RP235x.

Cave in a Box: a Compact, Handheld Display Device for Cave Holograms (9-11)
Previously, <span class="author">John Klayer</span> described methods for making holograms in a cave environment. That article briefly mentioned a small box that fits in a pocket to display the finished hologram. Here he gives some practical advice for those wanting to build one.

Building Blocks (12)
Use of computer modelling techniques for determining radio coverage - by <span class="author">Tony Haigh</span>.

Radiolocation Applied to Cave Surveys (13-14)
Surveyors and radiolocators seem to have parallel existences, with radiolocation rarely if ever being used as an input to surveys. <span class="author">Luc Le Blanc</span> reflects on this topic following a request by a user of Auriga, his mobile cave survey freeware.

An Android App for Processing Radiolocation Data (15-16)
<span class="author">V&iacute;ctor Porto</span> describes an Android app that he has written to simplify the calculation of depth from radiolocation data. Features include: depth calculation by the magnetic field angle (angle method), or by signal strength (ratiometric method).

Electric and Magnetic Field Measurements around a Loop Antenna (17-18)
Following tests that showed LF communication using a loop antenna could achieve a range that was in the radiative far field, <span class="author">Ian Drummond</span> presents the results of tests to judge whether a whip - that is, an E-field antenna - would offer a viable alternative to the more cumbersome loops.

Mechanically Powered Transmitters at VLF and Below (19-21)
<span class="author">Mike Bedford</span> delves into methods of generating signals at the bottom end of the radio spectrum that rely on mechanical instead of electronic techniques.

Improving the Performance of a Cylindrical Coil Antenna for Radiolocation (22-24)
<span class="author">Ken Smith</span> and <span class="author">Aren Leishman</span> describe their work in enhancing the cylindrical coil antenna for use in a new version of the Pinger radiolocation system which is intended for use by divers in flooded passages.