How to Use Filter Equations in Software and Spreadsheets

Do a WWW search for filter equations and you will find thousands of pages, including a few here on RF Cafe. However, if you want an example of how to implement the transfer functions in a spreadsheet or software, examples of actual code are elusive (other than maybe a Matlab or MathCAD worksheet). As one who has incorporated equations for Butterworth, Chebyshev Type 1, Chebyshev Type 2, and other filter functions in many spreadsheets and software over the past few decades, I figured it might be useful to post snippets of my code so that someone else can copy and paste it directly into other work. BTW, I do not consider myself to be a filter expert by any means and there is no ground-breaking knowledge here; it's just hopefully easier to find. Writing a macro to use in a spreadsheet is the preferred...

Attack Planes Hug Hostile Terrain with New Radar

According to this 1964 article in Electronics magazine, the U.S. Air Force's decision to build radar systems that would enable low altitude, terrain-following flight paths for strategic and tactical aircraft was in response to the shooting down of Gary Powers' U-2 spy craft in 1960. The event made clear that simply flying high over enemy territory and dropping bombs would not be a reliable strategy since surface-to-air missiles could reach and destroy aircraft before they got to their targets. Terrain-following capability on the part of bombers and fighters would add a major element of surprise since approach paths could be masked until it was too late to take offensive action. That approach was not without its risks and faults, as made apparent by the Dr. Strangelove movie satire that poked fun at the very concept...

Antenna Reference Chart

Selecting the proper antenna for a particular application can mean the difference between success and failure when any combination of signal strength and/or signal interference is involved. Modern spread spectrum technologies has eased the job a bit, but there are still instances when high gain and/or directivity is necessary. You might be tempted to say that gain and directivity are essentially the same thing, and to some extent that is true. However, in the case of needing to minimize signal interference from surrounding sources, a directional antenna might be utilized not due to a need for increased desired signal strength but to reduce the power of undesired emitters. Such was often the requirement for television and FM radio reception. After years of needing to reorient the folded dipole antenna for my FM radio because...

Goddard Satellite Missions of the 1960s

America's first successful orbiting of a satellite launch happened on February 1, 1958 with the launch of Explorer 1 atop a Juno 1 rocket. Our first attempted satellite launch was the Vanguard TV3, on December 6, 1957, but it unfortunately succumbed to a failed booster rocket (it rose only 4 feet off the launch pad). Russia had already launched its Sputnik 1 satellite on October 4, 1957, making it the very first manmade satellite to orbit the earth - to the forever chagrin of U.S. scientists. Fortunately, advances occurred rapidly for the U.S. space program after Explorer 1. In its first full decade of existence, the Goddard Space Flight Center, located in Greenbelt, Maryland, was responsible for launching more than 100 different spacecraft...

How to Use Your Radio

This 1934 edition of Tower Radio magazine was thrown in with a batch of vintage radio magazines I bought on eBay. Most of the content pertains to entertainers of the day rather than with technical issues. Reportedly, it was only sold at Woolworth's stores. Ironically, the number of households with over-the-air (OTA) radio listeners today, at least as a percentage of the population if not in absolute numbers, is probably about the same as in 1934 when commercial radio broadcasting was just getting a foothold. These days, many - if not most - people listen to radio and podcasts via cellphone and/or Internet streaming media than from over-the-air broadcasts, even while in their cars. Organizations like the National Association of Broadcasters (NAB) are trying to change that, but it's an uphill battle. I tune in to OTA when possible, but with my radio sitting close to the computer with all the EMI it spews...

New Magnetron Shifts Frequency Fast

Frequency hopping spread spectrum, first proposed and patented by Hollywood actress Hedy Lamarr, relies on both transmitters and receivers to precisely tune in a pseudorandom manner to a band of discrete frequencies in a time-synchronized manner with each other. The faster an encoded signal hops between frequencies, the more difficult it is for an unintended listener to decode the message. Same goes for the number of discrete frequencies used in the spread spectrum scheme. Modern computer programs and fast-tuning receiver systems can gather huge amounts of information spread across a broad bandwidth and re-assemble it into intelligible data, and if an unlimited amount of time was available to do so, just about any message can be decoded...

War and the Radio Amateur

Amateur radio station operators seemed to always be amongst the first to lose their rights in time of war. Governmental power brokers - from unelected local bureaucrats on up to presidents - love to demonstrate their influence over citizens when the opportunity arises. The Radio Act of 1912 revoked the rights of amateur radio stations to operate, and in some cases authorized the confiscation of radio equipment for use by the government. Permission was not restored until 1919, after World War I. Amateurs took it on the chin again in World War II with revocation of licenses. In this 1917 article in The Electrical Experimenter publisher Hugo Gernsback makes the case for permitting "our red-blooded boys be trusted to assist our officials in running down spies." "...we realize how absurd it is to close all privately owned radio stations during the war..."

Magnetism - Its History

An ancient legend tells us that nearly 5,000 years ago an Emperor of China had a small statue of a man mounted on his chariot. This statue was pivoted at the base and one outstretched arm always pointed to the south. In those ancient times, this action must have seemed truly miraculous - probably the Emperor used his statue more to impress his subjects than he did to find his way. This legend is the first report of man's use of a black or lead-colored stone called magnetite. About the time of Christ, magnetite was rediscovered by a Grecian shepherd. He noticed that the iron of his staff was attracted to certain stones. But for nearly another 1,000 years, no particular use was made of this discovery...

Citizen Band Radios

Although "Citizens Band" (CB) is the common reference to these unlicensed two-way radio service transceivers, the official name for the spectrum allocated by the FCC to their operation is "Citizens Band Radio Service" (CBRS). It was originally called just "Citizens Radio Service," but the popular use of "Band" caused the FCC to incorporate the additional term later on. Early Part 95 Class D citizens band radios offered up to 23 channels in the 11-meter band from 26.965 MHz through 27.255 MHz. CB radio channels increased to 40 in 1977 due to the immense popularity at the time (long before cellphones) - recall the "Convoy" song. The 11-meter band was re-allocated from the amateur radio spectrum in 1958 (to the great dismay of Hams). CB radios are still used heavily by truckers who don't like the idea of "Big Brother" listening to and recording conversations...

1 to the 4th Power Amplification in Star Trek Redux

A few years ago I posted a note about a technical faux pas on an episode of Star Trek titled "Court Martial," where Captain Kirk makes a comment ordering the ship's auditory sensors to be boosted "on the order of 1 to the 4th power," (1⁴) in order to pick up heart beats. RF Cafe visitor Sam M. just sent me a note offering a possible - and plausible - explanation for the gaff. If you are a devoted Trekkie looking for a response to your apostate friends when confronted over the scene, read on...

RF Cafe Engineering & Science Crossword Puzzle for February 24

Beginning in 2000, I have created hundreds of custom technology-themed crossword puzzles for the brain-exercising benefit and pleasure of RF Cafe visitors who are fellow cruciverbalists. The jury is out on whether or not this type of mental challenge helps keep your gray matter from atrophying in old age, but it certainly helps maintain your vocabulary and cognitive skills at all ages. A database of thousands of words has been built up over the years and contains only clues and terms associated with engineering, science, physical, astronomy, mathematics, chemistry, etc. You will never find a word taxing your knowledge of a numbnut soap opera star or the name of some obscure village in the Andes mountains. You might, however, encounter the name of a movie start like Hedy Lamarr or a geographical location like Tunguska, Russia, for reasons which, if you don't already know, might surprise you...

A Look at the PC Market

When I first read the title for this article, "A Look at the PC Market," I was thinking personal computers, not printed circuits. It being from a 1972 issue of Popular Electronics, my assumption was that the photos of circuit boards were from early kit format computers, but then it finally dawned on me that there were no personal computers in 1972 - not even in kit form. Actually, that is not entirely true since there were advertisements for hokey contraptions called "computers" that combined some switches, logic gates, and LEDs for implementing simple multiple choice true/false testing boxes or rudimentary (with emphasis on "rud[e]") calculators. Getting to the real story, though, the 1970s was the decade where printed circuit boards (PCBs) were replacing point-to-point wiring wherever possible. If you opened a radio or television...

Electromagnetism - What It Is

Chapter 12 of the U.S. Navy's basic electronics training course discusses electromagnetism. It follows on the heels of the sections introducing magnetism and electrical currents. The Navy (and the Air Force, I must add) is renowned for its high quality training and for turning out graduates that perform highly in both their service duties and in private industry after separation. It describes the electromagnet as being like a natural or artificial magnet in its attractive force, is tremendous and can hold tons of iron. Because this magnet is powered by an electric current, the magnetism can be turned on and off with the flick of a switch. Electrically-powered magnets are called electromagnets. Electromagnets come in all sizes and shapes...

Variable-Voltage Tuning: How It Works

Have you ever used any of these voltage-variable capacitor (VVC) types: varicaps, epicaps, minicaps, voltacaps, capistors and varactrons? If you answered "no, but I have used varactor diodes," then the more correct answer would have "yes, I have, but by a different name." Construction was similar for all variations. This article from a 1969 issue of Radio-Electronics magazine reports on some of the earliest forms of diodes specifically designed to use a reverse bias on the PN junction to control the effective capacitance of the device for use in frequency tuning circuits. The first uses were for electronically tuning local oscillators in mixing stages, and then for making tunable filters. Capacitance ratios greater than 10:1 with some VVCs allowed tuning over a very wide range. At the time the article was written, there was not universally agreed upon schematic symbol for the VVC, as illustrated in Figure 2. Varactor-tuned television channel selectors...

The Operational Amplifier

There is no such thing as too many introductory articles on operational amplifiers (opamps). Of course, when this story was written for Electronics World back in 1967, opamps were relatively new to the scene. Prior to the advent of opamps, circuit design for controllers, filter, comparators, isolators, and just plain old amplification was much more involved. Opamps suddenly allowed designers to not worry as much about biasing, variations in power supply voltages, and other annoyances, and instead focus on function. Even from the very beginning with the μa741 operational amplifier, the parameters came close to those of an ideal device: infinite input impedance, zero output impedance, perfect isolation between ports, and infinite bandwidth. OK, the bandwidth spec was more constrained compared to the other three, but still, with frequencies...