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# format auto-updated on access: Tue 01-Dec-2020 12:15:46 +00:00 CREG Journal 112 (0-24) This issue has a cover date of December 2020 and was published on 1 December 2020. Front Cover (1) 3D rendering showing the stereo camera system in the textured model of the Grotta Giusti cave. Image: (FBK) and (AMU) Contents (2) List of contents and masthead information. News and Notes (2) Digital Signal Processing, A Cost-effective 3D Photogrammetric Approach for Semi-submerged Caves (3-6) , , and present a method, based on photogrammetry, to simultaneously survey the above and below water parts of semi-submersed caves. Single-board Computers for Data Logging and IoT Applications (7-9) Off-the-shelf SBCs could simplify the design of cave data loggers. presents an overview of suitable products. Strain Gauge Amplifier for Load Cells and other Fast-acting Signals (10-11) presents the work by Paul Thorne using two moderately fast-acting amplifiers to build a strain gauge amplifier for a Wheatstone bridge load cell with a rise and fall time of below 10 microseconds. We Hear (12) Roundup of news and events: brings us the latest to impact the world of cave radio and electronics. Drone Developments: Enter the Dragon, Triboelectric Energy Scavenging, Light Sticks Under the Spotlight. Underground Trials of Low-cost Coaxial Cables as Leaky Feeders (13-14) Following previous tests aimed at determining an ideal type of cable and operating frequency, , EA4HCN, reports on underground tests using low-cost coaxial cables as leaky feeders aimed at quantifying real-world performance. Building Blocks (15) Exploring what a basic GPS receiver can offer, by . An Introduction to GNU Radio (16-19) Digital Signal Processing offers many advantages over more traditional analogue approaches. presents an introduction to this DSP package, which can run on a Raspberry Pi. Letters to the Editor (20-21) Earth Resistivity Surveying, ; Earth Resistivity - Correction; Addressable Electrodes, . The Adventures of Greg (20) Illustration by , and words by . Web Watch (21) Fascinating links - from serious power tools, incredible charging speeds to powerful magnification, by . Update: Regenerative Brake (21) In an extension of his notes on regenerative braking, describes how to build an LED lamp that is powered by a falling weight. HF Cave Radio - The Story so Far (22-24) and summarise the results of several years of experimentation into cave radio at HF and suggest some avenues for further work.