## Transforming impedances: Question G5C07

In the last two weeks, I’ve received e-mails from two readers of The No-Nonsense General-Class License Study Guide. Both questioned my explanation of how transformers transform impedance. I wrote:

Transformers are also used to transform impedances. The impedance ratio is also related to the turns ratio, but the transformation is equal to the square of the turns ratio. The turns ratio of a transformer used to match an audio amplifier having a 600-ohm output impedance to a speaker having a 4-ohm impedance is 12.2 to 1. (G5C07)

Doug wrote, “The only way I can reproduce the calculation is by taking the square root of the turns ratio.” His comment made me see where my explanation could be a bit misleading. I wrote back:

Think about it this way. An impedance transformation can go either way. When transforming from a higher impedance to a lower impedance, you divide by the square root of the turns ratio. When transforming a lower impedance to a higher impedance, you multiply by the square of the turns ratio. In either case, the impedance ratio is “related” to the square of the turns ratio.

I love getting feedback from my readers. Feedback like this helps me improve my study guides. If you have used one of my study guides, and have a comment or question about any of the material, please feel free to contact me.

## From the trade magazines: litz wire, vector network analyzers, SDR

Another selection of amateur radio related items appearing recently in the electronic engineering trade publications.

Litz wire and other component cleverness
If you’re not familiar with it, litz wire is not named after a person or a place. It’s short for Litzendraht, the German term for braided, stranded, or woven wire. It’s a very clever solution to the problems and inefficiencies caused by the skin effect — as the frequency of the current that a wire carries increases, the current tends to go to the outside of the wire.

Vector network analyzers support versatile testing
Among the most valuable of RF/microwave test tools is the vector network analyzer (VNA), which can measure amplitude and phase with frequency. VNAs have long become associated with the measurements of complex impedance parameters—such as scattering (S) parameters—using the test data to design efficient impedance matching networks for the optimum transmission of high-frequency signals through active and passive devices and networks. At present, VNAs are available from both well-known and not-so-well-known instrument manufacturers, in both bench top and portable configurations for making measurements on high-frequency (HF) through millimeter-wave-frequency signals.

The scaling of CMOS technologies typically has a great impact on analog design. The most severe consequence is the reduction of the voltage supply. Imec and Renesas have managed to put a complete, high-performance SDR (Software Defined Radio) receiver into a 28nm CMOS process with a 0.9V power supply. The IC has everything except a PLL on a single monolithic chip. (See Figure 1.) This is an impressive integration of analog functionality.

## From the trade magazines: spectrum sharing, active filters, real capacitors

Passive components aren’t really so passive (Part 1): Capacitors. Transistors and ICs are considered active components because they change signals using energy from the power supply. Capacitors, resistors, inductors, connectors, and even the printed-circuit board (PCB) are called passive because they don’t seem to consume power. But these apparently passive components can, and do, change the signal in unexpected ways because they all contain parasitic portions. So, many supposedly passive components, like the capacitor shown below, aren’t so passive.

The model above shows that a capacitor adds more than just capacitance when you use it in a circuit.

Peaceful coexistence on the radio spectrum. How two engineers (shown at right) tried to get the military to share some spectrum with their small company.

Signal-chain basics #43: Active filters. While low-frequency filters can be designed with inductors and capacitors, they often require physically large and often expensive inductors. This is where active filters, which combine an operational amplifier (op amp) with some resistors and capacitors, become attractive. Active filters can provide an LCR-like performance at low frequencies

## From my inbox: interplanetary communication, emcomm router, 3.3V logic

From ACM Tech News 5/8/13. Now all we need are sub-space transceivers….Dan
Google’s Chief Internet Evangelist on Creating the Interplanetary Internet
Google chief Internet evangelist and ACM president Vint Cerf has been working for years on an interplanetary Internet with protocols capable of handling a space environment. Together with the U.S. National Aeronautics and Space Administration (NASA) and the Jet Propulsion Laboratory, Cerf has created an early-stage space-based network with a few nodes that he says are “the front end of what could be an evolving and expanding interplanetary backbone.” The project began in 1997 when Cerf considered what the Internet might need in 25 years, and concluded that NASA and other space-faring agencies would need greater networking capabilities. The interplanetary protocol has the capacity to store a large amount of data for a long time prior to transmission. If the protocol is adopted by the Consultative Committee on Space Data Systems, which standardizes space communication protocols, then all robotic and manned space missions will have the option of using these protocols. View Full Article

Also from ACM Tech News 5/8/13. Sound like something useful for emcomm….Dan
This Box Keeps Information Flowing During a Crisis

Technology Review (05/05/13) David Talbot
The creators of Ushahidi, a software platform for communicating information during a crisis, have developed BRCK, a Wi-Fi router that can connect with any network in the world, can provide eight hours of wireless connectivity, and can be programmed for new applications. The BRCK device can serve up to 20 devices when there is an Internet connection and connects to a cloud-based server that enables any BRCK user to monitor its performance remotely and manage alerts. The device also is programmable, apps can be written for it, and it comes with up to 16 GB of storage. “Once you understand what the product does–provides a reliable connectivity backup in places where power and connectivity are spotty–it’s hard to understand why no one has built the tool before,” says Massachusetts Institute of Technology’s Ethan Zuckerman, who serves on the board of Ushahidi. The nonprofit company says the purpose behind BRCK was to build the world’s most simple, reliable, and rugged Internet connection device, but with sophisticated cloud-based features. “No other single device does these off-grid communications, software cloud access, and remote management of sensors connected to it,” says Ushahidi co-founder Erik Hersman. View Full Article

From André N4ICK via the Tacos mailing list…..Dan

Temperature and voltage variation of ceramic capacitors. Read the data sheet! This tutorial explains how ceramic capacitor type designations, such as X7R and Y5V, imply nothing about voltage coefficients. You must check the data sheet to really know, how a specific capacitor will perform under temperature and voltage.

Circuit measures capacitance or inductance. You don’t need a fancy LC meter to measure capacitance or inductance. This short article show you how to do it with a function generator, multimeter, frequency counter, and an oscilloscope. Hmmmmm. By the time you get that all lashed up, it might have been quicker to just buy one of these LC meters from China.

Understand Radio Architectures. This is the first in a series of excerpts from the book RF Circuit Design, 2e by Christopher Bowick. Even though this appears in an engineering trade magazine, some of this is pretty basic stuff. You even get a schematic for a crystal radio!

## Wire and cable throughout the ages

The German Wire Museum (Deutsches Drahtmuseum) in Altena is all about wire and cable—from its use in chainmail in the Middle Ages through superconductors today. Just reading the story about the museum is a real eye-opener. As hams, we tend to think of wire and cable as electronic components, but wire has been used down through the centuries in jewelry, in pianos, in bridges, and many other applications. Interesting stuff.

## On the Internet – 11/26/12

WITCH gets a reboot. The world’s oldest digital computer was brought back to life by engineers at The National Museum of Computing in Buckinghamshire, England. The computer was first turned on in 1951 and uses 480 relays and 828 vacuum tubes called Dekatrons, which store ten discreet values. EETimes also ran a story on this computer.

First Visible LED Demoed 50 Years Ago. Since we’re doing history today, here’s a link to a Wired article marking the first demonstration of an LED that emitted visible light. The article notes, “In the February 1963 issue of Reader’s Digest, Holonyak predicted that the LED would eventually replace incandescent bulbs. Bold words from a man who worked for GE, a company founded by Thomas Edison.” We’re finally getting around to this 50 years later.

How to Listen to Real Spy Broadcasts Now. Lifehacker shows you how to dial in to numbers stations and the like. The article says, “The behavior of shortwave radio in the atmosphere makes it ideal for long range radio transmission. You can send messages on a given frequency all over the world, and most people who use shortwave radio use it to communicate with ships at sea and people in locations all over the world.”

## Book tells you not only how to use components, but what can go wrong when you do

Encyclopedia of Electronic Components – Volume 1
By Charles Platt
O’Reilly Media, 2012, 278 pages.

The Encyclopedia of Electronic Components is the latest from Make: magazine, part of the O’Reilly empire. Like all of their publications, this book is well-written, well-illustrated, and if you’re just getting started in amateur radio or electronics, it would make a great addition to your library.

The nice thing about this book is that it not only talks about what a component does and show you the schematic symbol for a particular type of component, it also talks about typical applications for a component and what can go wrong with that type of component. Let’s compare how the 2005 ARRL Handbook (the latest version that I have) discusses resistors  with how The Encyclopedia covers resistors.

The 2005 Handbook devotes about a page and a half total to resistors, including:

• four paragraphs on the fundamentals of resistance in the chapter Electric Fundamentals,
• twelve paragraphs on different resistor types in the chapter  Real World Component Characteristics, and
• a half page on resistor markings in the chapter Component Data and References.

It’s also very chintzy with illustrations. I only count one chart and one drawing.

The Encyclopedia, on the other hand, devotes an entire chapter to resistors, with 17 illustrations and two charts. The chapter not only covers theory, but also discusses practical applications, including how they’re used to limit current, bias a transistor, and pull up or pull down voltages in a digital logic circuit.

I also love the “What Can Go Wrong” section. This section describes how resistors can overheat, introduce noise into a circuit, and how tolerances can affect circuit operation. The book takes this approach to discussing a wide variety of electronic components, including batteries, switches, relays, encoders, capacitors, motors, and semiconductor devices, so no matter what kind of electronics you’re hacking, this book has some good info for you.

## Interesting tidbits from the Internet – Homemade tools, more kits, a CMOS replacement

This set of links include a website for homemade tools, another source of kits, and a report on an electronic technology to replace CMOS.

This manual pick-and-place station is one of many that you’ll find on HomemadeTools.Net that are useful for amateur radio operators.

Home-made tools. This is a new site from the founder of Hotrodders.com, established to organize all of the homemade tools posted on forums and websites around the net. The site currently has nearly 3,000 different homemade tools, with new tools added regularly. Be sure to check out the electrical section, which has many tools that you can use around the ham shack. It includes a \$3 battery charger, a low-cost 12 V benchtop power supply, and a manual pick-and-place station to use when building with surface-mount components.

Kits by K5BCQ, K5JHF, and the Austin QRP Club. Kees, K5BCQ; John, K5JHF; and other members of the Austin QRP Club are making available some useful kits at reasonable prices to encourage kit building and homebrewing. The kits are all based around readily available, low-cost microcontrollers, flash memory, and LCD displays. I’m thinking about buying the The Si570 Controller and Frequency Generator Kit #2. At \$54 or less, I think it’s a steal.

NRI to lead new five-year effort to develop post-CMOS electronics. This article from the NIST Tech Beat describes a project to develop a next-generation electronics technology to replace the venerable CMOS technology. According to the article, new technology is needed because pretty soon IC manufacturers won’t be able to make transistors any smaller.

## Extra Class question of the day: Frequency counters and markers

To measure the frequency of a signal, you use an instrument called a frequency counter. The purpose of a frequency counter is to provide a digital representation of the frequency of a signal.(E7F09) A frequency counter counts the number of input pulses occurring within a specific period of time. (E7F08)

To accurately measure high-frequency signals digitally, you need a highly stable and accurate frequency source, called the time base. The time base provides an accurate and repeatable time period, over which you count the number of pulses of the test signal. The accuracy of the time base determines the accuracy of a frequency counter. (E7F07)

An alternate method of determining frequency, other than by directly counting input pulses, that is used by some counters is period measurement plus mathematical computation. (E7F10) An advantage of a period-measuring frequency counter over a direct-count type is that it provides improved resolution of low-frequency signals within a comparable time period. (E7F11)

You also need an accurate and stable time base to generate and receive microwave signals. All of these choices are correct when talking about techniques for providing high stability oscillators needed for microwave transmission and reception: (E7F05)

• Use a GPS signal reference
• Use a rubidium stabilized reference oscillator
• Use a temperature-controlled high Q dielectric resonator

If you want to measure a signal whose frequency is higher than the maximum frequency of your counter, you might use a prescaler. The purpose of a prescaler circuit is to divide a higher frequency signal so a low-frequency counter can display the input frequency. (E7F01) A prescaler would, for example, be used to reduce a signal’s frequency by a factor of ten. (E7F02)

You might use a decade counter digital IC in a prescaler circuit. The function of a decade counter digital IC is to produce one output pulse for every ten input pulses. (E7F03)

In some cases, you might use a flip-flop. Two flip-flops must be added to a 100-kHz crystal-controlled marker generator so as to provide markers at 50 and 25 kHz. (E7F04) The purpose of a marker generator is to provide a means of calibrating a receiver’s frequency settings. (E7F06) You mostly find marker generators in older, analog receivers.