Radio Mirrors for Communications

Passive repeater antennas have been used for a long time to overcome line-of-sight-limitations of many - if not most - of the radio communications universe. Properly designed and implemented passive repeaters can exhibit very high levels of efficiency, and in some cases can actually provide gain by focusing signals impinging on a large panel of multiple wavelength dimensions onto a smaller transmitter or receiver antenna. That is known as aperture gain. Optical telescopes are a good analogy where for the same level of magnification at a given wavelength, a larger aperture (refractive lens or reflector mirror) results in a brighter image at your retina or CCD...

R. F. Interference Filters

Sprague Electric engineer Benedict Rosen, discusses how the characteristics of a circuit in need of protection against RF interference needs to be considered when selecting filter components. He points out that attempting to hang a shunt feedthrough capacitor on the input and/or output of a low impedance (e.g., 50 Ω) RF circuit could make the situation worse, depending on whether the circuit is strongly capacitive or inductive in its out-of-band region. Sprague was a major manufacturer of all sorts of capacitors qualified for use in military and aerospace systems, so they put a lot of effort into characterizing device parameters over a wide range of voltage, current, power, temperature, mechanical, and frequency environments...

UJT Monostable / Monocycle Multivibrator

Monostable multivibrator, one-shot multivibrator, monocycle multivibrator - it's a matter of semantics, although the circuit designer doesn't necessarily think so. The distinction, evidently, is that this monocycle multivibrator uses a positive-going pulse as a trigger and the output in its rest (stable) state is a digital "0" (low). A mere 2 mA of current flows since all the unijunction transistors (UJTs) are turned off. A UJT, to refresh your memory, is not used as a linear amplifier because of its regenerative, negative resistance operating region that causes it to effectively lock into a fully on or fully off conduction state until an external stimulus causes...

Capacitance Probes in Industrial Instrumentation

Simmonds Precision Products, a company in Vergennes, Vermont, which I worked for for a couple years prior to quitting to attend the University of Vermont full-time to finish my electrical engineering degree, had as one of their main products capacitance-based fuel measurement systems for military and commercial aircraft. As was common in the era, they made not only the capacitance probes and associated electronics, but also the cockpit displays and power supplies. Being a test technician at the time, I got a pretty good exposure to the complexities of such a fundamentally simple principle as using the...

Effective Radiated Power

EIRP - effective isotropic radiated power - is an important parameter when calculating both intentional and unintentional electromagnetic emissions. EIRP is a vector quantity that accounts for both power (magnitude) and 3-dimensional coordinates (direction). It includes antenna directivity that concentrates power in a particular direction rather than distributing it equally in all directions (e.g., isotropically). Effective radiated power factors in modulation type and power envelope shape as well. Knowing how to measure that quantities can make the difference between...

Crystal Filters

As with most technologies that have been around for decades, the fundamentals of crystal filters have not changed with time. Materials and methods have changed, of course, but the equivalent lumped element model (using resistors, capacitors and inductors) of a crystal filter is essentially the same today as it was in 1969 when this article appeared in Electronics World magazine. Open a first semester electronics circuits textbook and the chapter on crystals will look much like this piece by Mr. Robert Kent, of Damon Engineering. The use of crystal had a profound impact on filter design because their extremely high "Q" factors...

Tips for Technicians

Did you know that Mallory, the well-known capacitor maker, at one time was at the forefront of solid state rectifier diodes? Not me, at least before seeing this infomercial from a 1969 Electronics World magazine. I know that they made selenium rectifiers that replaced many application which formerly required vacuum tubes. This installation of Mallory's "Tips for Technicians" is one of many run for the benefit of service shop guys who needed to keep abreast of changes in technology. Note the admonition at the end: "Don't forget to ask 'em - 'What else needs fixing?'"...

Wartime Solder

Prior to the big push for leadless solder in the 1990s, probably 99% or more of the solder used by industry, tradesmen, and hobbyists contained lead. The 60/40 Sn-Pb (and 63/47) alloy, both with and without a rosin or acid core, was used for electrical work, electronics, plumbing, copper guttering, radiators, and many mechanical assemblies made of steel, brass, copper, tin, etc. Between World War I, "The War to [Not] End All Wars," and World War II, the electronics industry exploded in growth. All realms of society and government became utterly dependent on products assembled using solder. Both tin and lead were abundantly available...

Crystals for CB & Ham Communication

According to author R.R. Freeland, manufacturing processes for radio-quality manmade crystals saw major improvements toward the end of World War II. At the time, the process was highly manual-intensive, as can be seen in this really nicely done 1940s video titled "Crystals Go to War." Prior to the use of crystals as frequency-determining devices, inductor-capacitor (LC) tank circuits were the dominant configuration. There were actually other frequency-determining schemes like spark gaps and even vibrating mechanical reeds. As you might guess, anything less than...

RF Cafe Engineering Crossword Puzzle w/Weekly Headlines

At least 10 clues with an asterisk (*) in this technology-themed crossword puzzle are pulled from this past week's (1/8 - 1/14) "Tech Industry Headlines" column on the RF Cafe homepage (see the Headline Archives page for help). For the sake of all the avid cruciverbalists amongst us, each week I create a new technology-themed crossword puzzle using only words from my custom-created related to engineering, science, mathematics, chemistry, physics, astronomy...

Comsat Laboratories Needed Electronic Technicians

For the benefit of RF Cafe visitors, I have posted at no charge to companies many employment announcements for engineers, technicians, managers, and other technical positions. This electronics technician job was located at COMSAT Laboratories' (Communications Satellite Corporation) Washington, D.C., facilities since 1969 was prior to when the then-futuristic-looking Clarksburg, Maryland, campus was established. In the early 1990s, I worked as an RF design engineer for a few years at COMSAT Laboratories in Clarksburg. About a decade earlier, before earning my BSEE degree, I was working as an electronics technician at ...

A Few More Electronics-Themed Comics

TGIF. If this past week has had you on edge, cheer up -the weekend's almost here. Once the final fire has been put out - or is at least contained - give yourself a break and enjoy these tech-themed comics from a vintage issue of Electronics World magazine. My favorite is the one on page 83 which is a takeoff on the well-worn comedy meme of the husband trying to sneak back into the house after a night out with the boys. This poor guy has been outwitted by his wife, who evidently has a bit of tech savvy working for her...

Atomic Radiation: Types & Relationships

Nuclear energy was a big topic in the 1960s and 1970s as it was believed to be the future of electrical power generation for the world (at least up until the 3 Mile Island and Chernobyl incidents occurred). Ships and submarines were being powered by reactors that allowed them to run for months at a time without refueling, atmospheric emissions were practically zero, and the fuel source was abundant (albeit not simple to obtain). Medical and space applications were increasingly dependent on a greater knowledge of radiation and its effects on humans, plants, animals, and electronics. Many people by that...

Cleveland Institute of Electronics Advertisement

As mentioned often here on RF Cafe, especially with an ever-increasing amount of devices and appliances with "no user serviceable parts inside," the demand for electronics technicians is as great today as it was decades ago. Associated equipment is significantly different now and a lot more of it consists of swap-out modules and assemblies rather than performing repairs in the field. However, there still exists a significant amount of legacy electronics everywhere, and it all needs to be maintained until upgrades are installed. There...

News Highlights, July 1972 Popular Electronics

Engineering and science magazines, websites, and discussion panels frequently report on and lament the lack of women and minorities in both realms. You might think this is a relatively new concern since, but as evidenced by this 1972 Popular Electronics tidbit the effort to attract women and minorities into the fields has been going on for half a century. At the time, women and minorities made up about 2% of undergraduates in engineering curricula. The proportion was 20% as of 2015 according to a recent report by the ASEE. During that same time period (1970), according to the National Center for Education...