I'm happy to announce that the No-Nonsense Extra Class License Study Guide is now available. The No-Nonsense series of amateur radio license study guides has become famous for helping people pass the tests. Written in a simple, easy-to-understand style, this study guide will help you upgrade to Amateur Extra Class. Here's an excerpt: Digital circuits are used for a variety of functions in modern amateur radio equipment. Unlike analog circuits, the output voltage of an ideal digital circuit can only be one of two values. One of these voltages—normally a positive voltage—represents a digital 1. The other value—normally near 0 V—represents a digital 0. This type of logic is generally called positive logic. Positive Logic is the name for logic which represents a logic '1' as a high voltage. (E7A11) The logic may be reversed, though. That is to say that a high voltage may represent a logic 0. Negative logic is the name for logic which represents a logic '0' as a high voltage. (E7A12) The microcomputers that control today’s transceivers, for example, are very complex digital circuits. These complex digital circuits are made by combining many smaller building blocks called logic gates. These gates perform basic digital logic functions. One of the most basic digital circuits in the NAND gate. The logical operation that a NAND gate performs is that it produces a logic '0' at its output only when all inputs are logic '1.' (E7A07)The study guide costs $7.99, and is available from my website, Amazon.Com, or Barnes&Noble.Com. For more information on the Extra Class study guide, as well as my other study guides, go to http://www.kb6nu.com/tech-manual.