OpenSK https://github.com/google/OpenSK released by Google is a fully open-source implementation for security keys written in Rust that supports both FIDO U2F and FIDO2 standards.

OpenSK is based on the FIDO2 specifications, which combine the World Wide Web Consortium’s (W3C) Web Authentication (WebAuthn) specification and FIDO Alliance’s corresponding Client-to-Authenticator Protocol (CTAP).

The nRF52840 MDK USB Dongle works well with OpenSK. Taking advantage of the UF2 Bootloader, you can easily program the OpenSK by just copying the .uf2-format image to the flash drive.

How to measure the number of correctable errors on CDs to judge the quality.
Found via https://reproducible-builds.org/who/projects/ which links to https://www.fabiankeil.de/gehacktes/electrobsd/

All parts 3D printed from PETG material, UV resistent and water proof. Found via https://www.rtl-sdr.com/techminds-building-a-3d-printed-2-4-ghz-dual-feed-helix-for-qo-100/ and https://www.qrz.com/db/DC8PAT
See also https://www.rtl-sdr.com/receiving-x-band-images-from-the-arktika-m1-arctic-monitoring-satellite/, https://www.rtl-sdr.com/a-comprehensive-beginners-guide-to-hrpt-weather-satellite-reception/

On/Off button with USB interface based on Arduino. Includes links to information about HID.

Interface circuit to attach a Sun type 5 keyboard to a PC, using a 68HC11 microcontroller.

The best compromise between sensitivity and portability
by Luca Feletti and Renato Romero. PCB layout by Jochen Richert.

Detailed description of a shielded magnetic loop antenna for VLF signals

The tinyPFA is a Phase Frequency Analyzer, it is a portable, battery operated, two input device with a 4 inch display that can measure very precise frequency and phase differences between the signals applied to both inputs. The input frequency can be any frequency between 1 MHz and 300 MHz. Typical use is to measure the differences between two 10 MHz clocks. The tinyPFA can numerically display the phase and frequency difference, show the measurement in a graph versus time, store the measurements on a SD card inserted into an SD card slot, or send the phase measurements over USB to a PC, running a program such as TimeLab, for further display and processing. Phase and Frequency measurement accuracy is better then 1e-12 divided by the measurement time in seconds with decimation set to 1 Be aware the maximum frequency difference that can be display depends on the measurement time (Tau) and is approximately 0.4 / (Tau in s) so for Tau is 1 s it is 0.4 Hz maximum difference.

Found on https://soldersmoke.blogspot.com/2017/05/indonesian-bitx-check-out-britx.html

Found on http://www.aaronsplace.co.uk/blog/2018-04-03-gpib-arduino.html