From Rohde & Schwarz, here’s an excellent treatise on the the decibel (db) and its applications.
From the RF Designline web site here’s a 3-part series titled Understanding RF Instrument Specifications. There is lots of good information on various RF measurements and specifications. Part 1 Part 2 Part 3
They’re not hen’s teeth, but omnidirectional VHF/UHF/SHF antennas are more difficult to find than high-gain directional antennas. Both have their place in weak signal work. Some sources include: WIMO maker of the Big Wheel, The Olde Antenna Lab, and KU4AB Antennas. GM3SEK’s Amateur Radio Technical Notebook contains a broad range of good VHF/UHF reference information including information on antenna stacking.
The Care and Feeding of the R.F. Isolator on the EMR web site is an excellent treatise on the theory and application of RF isolators.
RF Cafe is a unique portal of RF, microwave, wireless, and other engineering resources. Vast collection of equations, references and conversions for electrical, mechanical, physical, and mathematical fields. Links for vendors, app notes, test notes, ham radio, magazines, books, active forums, patent and communications standards, technical crossword puzzles, quizzes, and much more.
NovexComm provides rack mounts for many amateur and shortwave radios as well as rack mount speaker panels.
The Repeater Builder’s Technical Information Page is an informational help site by Kevin Custer W3KKC This is the largest repeater information site in the world!
Benchtop Calculator is a small (72 kB) application that provides lots of engineering functions, many of which are handy for ham radio work. I’ve also found this freeware calculator distributed in a file called mantissa.exe. Just copy the file to your directory of choice and double click on it (or set up a shortcut) to run it – no fancy installation process is required. A glance at the screenshot reveals the veritable potpourri of RF-related conversions and calculation functions. The program uses a slightly unconventional method for data entry. Most values must be entered in the Data Input Module area followed by clicking Enter in the desired conversion/calculation area to use the value.
All About Electronics provides a series of online textbooks covering electricity and electronics. The information provided is great for both students, hobbyists, and professionals who are looking to expand their knowledge or “bone up” on their electronics knowledge. These textbooks were written by Tony R. Kuphaldt. The information is extensive so I’ve not had the opportunity to read all of it. However, I’ve looked over a number of pages and found them to be accurate and easy to understand. There are video lectures and even tests if you wish to hone your skills.
Reading Transistor Markings – a ‘secret decoder ring’ for various semiconductor base part numbers. (This is a 61 kB file.)