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#sandbox: Journal 115 has gone to press and is due for publication in September 2021
CREG Journal 115 (0-24)
This issue has a cover date of September 2021 and was published on 1 September 2021.

Front Cover (1)
Experimenting with 3D lidar modelling on an iPhone 12 in the short Högberget cave in Kirkkonummi, Finland. Photo: Jarmo Ruuth and Jari Arkko

Contents (2)
List of contents and masthead information.

News and Notes (2)
Subscriptions, CREG Committee. Rob Gill.

Experimenting with 3D Lidar Modelling on Latest iPhones (3-5)
The iPhone 12 Pro models have a lidar sensor that can be used to build 3D models of objects and rooms. Jari Arkko describes how he has used this facility for low-cost cave surveying in 3D. Although still an experimental technique, it has been used with impressive results in Lummelunda Cave, Gotland, Sweden.

Overview of Methods for Modelling Radio Propagation along Cave Passages (6-8)
Mike Bedford presents a summary of the main methods of modelling radio propagation along cave passages, with a view to planning a system and predicting performance.

Building Blocks (9)
Options for sourcing a printed circuit board. By Tony Haigh.

A Simple Class-D Single-Sideband Modulator (10-13)
David Gibson describes how the output pulses from two class-D double-sideband modulators using carrier-frequency PWM (CF-PWM) can be interleaved to create a class-D single-sideband modulation. The method, assumed to be novel, is simple enough to be implemented on a standard micro-controller, which means that it is more accessible to hobbyist designers than a DSP implementation.

We Hear (14)
Roundup of news and events: Mike Bedford brings us the latest to impact the world of cave radio and electronics. Walking Robot for Cave Exploration, Introducing PlasticArm for IOT and Beyond, Move Over Li-ion Here Comes Al-ion.

Letters to the Editor (15)
Rugged Cases, Luc Le Blanc; The Next CREG Field Meeting, Rob Gill.

Web Watch (15)
Peter Ludwig considers improved batteries, exciting night-vision developments, ultrasonic hearing with spatial awareness and using AI drones to peer through leafy canopies.

Data Protocol and Coding Examples for the British Cave Science Centre (16-20)
The British Cave Science Centre (BCSC) at Poole’s Cavern in Derbyshire has been fitted with sensors and data loggers in support of a number of cave science projects. The sensors transmit their data to the Internet via a broadband telephone connection. Two data protocols are used, essentially a ‘push’ and a ‘pull’ operation, which David Gibson describes as ‘Source-As-Browser’ and ‘Source-As-Server’. Each method has its advantages and disadvantages, which are explained in this article, that also gives examples of the code needed to handle the operations.

Presenting an Easy-to-Build Arduino-based Data Logger for Monitoring Water Levels (21-24)
Brendan Hall describes a low-cost Arduino cave data logging device, for tracking in-cave water levels, and presents the results of his initial trials that were carried out in Sleets Gill Cave. Practical information is provided to allow others to build the data logger.