Science & Nature
1439 sites
Subcategories:
- Astronomy & Space (396)
- Chemistry (8)
- Earth Sciences (26)
- Biology (79)
- Physics (30)
- Mathematics (59)
- Weather & Climate (104)
- Amateur Radio (682)
- Electronics (47)
http://discovercircuits.com/
DiscoverCircuits.com, run by engineer Dave Johnson P.E., is a massive repository of over 45,000 free electronic circuits and schematics cross-referenced across 500+ categories for engineers, hobbyists, inventors, and students. Online since 2002, it serves as a go-to reference for quick design ideas, circuit solutions, and component resources covering an enormous breadth of electronic applications.
https://exoplanet.eu/home
The Encyclopaedia of Exoplanetary Systems, maintained by a dedicated research team since 1995, catalogs over 8,000 confirmed extrasolar objects with filtering, sorting, and export tools for professional and amateur astronomers alike. Visitors can explore databases on binary star systems and circumstellar disks, generate online plots, view planetary systems in 3D and even virtual reality, and browse an exhaustive bibliography of exoplanet discoveries.
https://w4atc.ncsu.edu/
W4ATC is the Student Amateur Radio Society at NC State University, a club with over 90 years of history connecting students through the hobby of amateur radio. Visitors can explore the club's equipment archive, QSL information, moonbounce (EME) presentations, and details on joining the active campus radio community.
http://big.or.jp/~jh4phw/index-e.html
The personal ham radio homepage of an operator holding multiple callsigns including JH4PHW, JA1CUF, WH0P, and 9V1PW, reflecting activity across Japan and other regions. The site offers links to amateur radio resources, a callbook lookup, and a Japanese ham radio web cluster.
http://ka7oei.blogspot.com/2026/03/modifying-mfj-5008-parabolic-ultrasonic.html
KA7OEI is Clint's technically-focused amateur radio and electronics blog, covering hands-on modifications and experiments with devices like the MFJ-5008 parabolic ultrasonic receiver. This particular post dives deep into improving the sensitivity and frequency response of the discontinued ultrasonic tool, with detailed photos, circuit analysis, and practical applications like bat detection and power line fault finding.
https://aty.sdsu.edu/glossary.html
Andrew T. Young's comprehensive glossary defines technical terms used in atmospheric optics, covering phenomena like green flashes, mirages, and refraction drawn from optics, meteorology, astronomy, and geodesy. With 26 major sections and nearly 200 cross-linked entries, it serves as an authoritative reference for anyone studying how light behaves in Earth's atmosphere.
http://smallwonderqrp.blogspot.com/
K.P.S. Kang's blog dedicated to QRP (low-power) radio building, featuring homebrew transceiver projects, circuit schematics, and PCB layouts for minimalist radio construction. Posts cover topics like speech processors, SSB transceivers, and the FIREO low-power transceiver design, making it a useful resource for amateur radio homebrewers.
http://donklipstein.com/
Don Klipstein's sprawling technical resource covers everything from LEDs and fluorescent lamps to Tesla coils, xenon strobes, lasers, and high voltage experiments. With decades of accumulated hobbyist knowledge, detailed guides, and regularly updated content, it's an indispensable reference for electronics enthusiasts interested in lighting and discharge lamp technology.
http://t-hunter.org/
The Southern California Transmitter Hunters is a club dedicated to amateur radio direction finding (RDF), where participants use specialized antenna equipment to track down hidden transmitters. The site covers upcoming hunts, past results, equipment guides, hunt boundaries, and stories from the field, making it a rich resource for the local ham radio foxhunting community.
http://letarc.net/
LETARC appears to be a local amateur radio club or organization, with the URL structure suggesting an established regional radio group. The site likely serves as an online home for club members and enthusiasts interested in amateur radio activities and communications.