2014 Tech study guide: SWR and antenna measurements

In the 2010 study guide, this section was part of the section on feedlines and connectors. I think it makes more sense to separate it like I have here. There is one added question in this section T7C13 asks what a dummy load consists of…Dan

Standing wave ratio is a term you’ll often hear when talking about antennas and feedlines. In general terms, standing wave ratio (SWR) is a measure of how well a load is matched to a transmission line. (T7C03) In this context, the “load” is the antenna. When we say that an antenna is matched to a transmission line, we mean that the impedance of the transmission line is equal to the impedance of the antenna.

The reason it is important to have a low SWR in an antenna system that uses coaxial cable feedline is to allow the efficient transfer of power and reduce losses. (T9B01) The bigger the mismatch is between the feedline and the load, the higher the SWR will be, and the more power you will lose in the feedline. Power lost in a feedline is converted into heat. (T7C07) Power converted into heat is not radiated by the antenna, meaning your radiated signal will be weaker.

You can measure the SWR of your antenna system with an SWR meter. You usually connect the SWR meter near the output of your transmitter because it is important to have a low SWR at that point. A directional wattmeter is an instrument other than an SWR meter that you could use to determine if a feedline and antenna are properly matched. (T7C08)

1 to 1 is the reading on an SWR meter indicates a perfect impedance match between the antenna and the feedline. (T7C04) 2 to 1 is the approximate SWR value above which the protection circuits in most solid-state transmitters begin to reduce transmitter power. (T7C05) An SWR reading of 4:1 means that there is an impedance mismatch. (T7C06)

One way to ensure that the impedance of the antenna system matches the output impedance of transmitter is to use an antenna tuner. An antenna tuner matches the antenna system impedance to the transceiver’s output impedance. (T9B04)

In addition to the SWR meter and the directional wattmeter, there are a couple of other types of test instruments commonly found in an amateur’s “shack.” One instrument that every shack should have is the dummy load. A dummy load consists of a non-inductive resistor and a heat sink. (T7C13) The primary purpose of a dummy load is to prevent the radiation of signals when making tests. (T7C01)

Another common test instrument is the antenna analyzer. An antenna analyzer is an instrument that can be used to determine if an antenna is resonant at the desired operating frequency. (T7C02) You can also make a number of other measurements that will help you set up an antenna system, such as SWR, capacitance, and inductance.

From my Twitter feed: radio gifts,

RadioSurvivor's avatarRadio Survivor @RadioSurvivor
There’s got to be someone on your list who wants a radio purse radiosurvivor.com/2013/12/02/hol…

Check out the radio tower tie….Dan

HamRadioSupply's avatarAmateurRadioSupplies @HamRadioSupply
New post: What the heck is a grid dip meter? goo.gl/C9BTnR

I wrote this yesterday for the AmateurRadioSupplies.Com blog…Dan

ARRL_PR's avatar

Get tips on #HamRadio PR & promotion! The December issue of #ARRL‘s CONTACT! has been posted! bit.ly/bRzdks

From the trade magazines: satellite tracking, online circuit design, open-source test board

More cool stuff from the electronics engineering trade magazines….Dan

LEO satellite tracking in your backyard. Learn how one guy built his own satellite tracking system in his backyard.

The rise of the online circuit-design collective. Though still in the infancy stage, design and simulation tools that run entirely in the browser are pushing their way onto the EDA landscape. The ultimate goal is that they become essential players within the realm of professional design.

Test and measurement  turns to open source, Kickstarter. The field of test and measurement is set to benefit from open-source software applications if a Kickstarter fundraising project is successful. The Red Pitaya is a credit card-sized, reconfigurable measurement board with 60MHz of input bandwidth and an onboard Xilinx Zinq FPGA to perform signal processing.

How to build a WWVB receiver?

A recent news story about the 50th anniversary of WWVB got me to thinking about building my own WWVB receiver. I Googled “wwvb kits” and came up with the following:

Unfortunately, all of these kits use a little PC board made by a company called C-MAX, and the company has either discontinued making the IC that powers this module or simply quit selling this module in the U.S. As recently as a couple of years ago, Digikey actually sold this module for about seven bucks.

There are several Web pages that show how to interface the CMMR-6 module to an Arduino or a PIC processor. Here are two:

A couple of companies in the UK seem to still have the modules in stock. The price from a company called Earthshine is only six pounds, but that doesn’t include shipping, of course.

There are some plans that don’t  use the C-MAX chip, but, of course, they’re much more complex. One guy designed his own receiver, but it’s quite a bit more complex than simply using a single chip. There are also several commercial receivers available, but the cheapest one I found is $220.

There are several Web pages that describe how to use the WWVB receiver modules from “atomic clocks.” One of the projects scavenges the WWVB module from a Sony clock. The second uses the module from an Atomix 13131. The Atomix 13131 costs as little as $13.

So, I’m still unsure which way I’m going to go here, but it looks as though hacking an existing clock might be the way to go, especially if I can find one at a thrift shop or garage sale.

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.

Integrated RF analog, multi-standard, software-defined radio receivers
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 my Twitter feed: no code test, Contest U, iPhone sig gen

NO CODE TEST! If that don’t grab ‘em, I argue MIGHT AS WELL! Outreach according to http://www.dashtoons.com  #hamr #qrp pic.twitter.com/vAngtDNmmu

Matt MaszczakMatt Maszczak @rocknrollriter
For the new or newer op looking into contesting: http://www.arrl.org/news/view/dayton-contest-university-videos-available-on-youtube?utm_source=twitterfeed&utm_medium=facebook …

Jacob BeningoJacob Beningo @Jacob_Beningo
Turn a Smart Phone into a Signal Generator | EDN http://www.edn.com/electrical-engineer-community/industry-blog/4416138/1/Turn-a-Smart-Phone-into-a-Signal-Generator … via @edncom

From the trade magazines: capacitors, inductors, radio architectures

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!

From my Twitter feed: HF receivers, voltage reference, FDIM

A History of HF Receivers | Smoke Curlshttp://t.co/A2uHc38mic #hamr


Erl’s voltage referencehttp://t.co/X0MOESc8BO

I need to build one of these……Dan


qrparciFDIM 2013 (Dayton) – Full seminar schedule now online http://t.co/9eWdTI0FEx #hamr#qrp #hamvention

I’ll be attending FDIM. If you see me, say hi….Dan

You need a digital multimeter

I’ve decided that my next book is going to be about multimeters. Here’s a draft of the first chapter…Dan

Digital multimeters, or DMMs, are the most commonly-used test instruments by electronics engineers, technicians, and hobbyists to design, build, and troubleshoot electronic circuits. If you work with electronics or electrical circuits, either as a professional or as a hobbyist, you need a digital multimeter. Without one, it’s almost impossible to adjust or troubleshoot circuits.

Let me give you an example. About a year ago, my brother, Michael, decided that he was going to purchase a very-used shuffle bowling machine at an estate sale. This is the kind of coin-operated machine that you would often in bars. Put in a dime and it would allow you to “bowl” a game.

The unit he purchased was built in the late 1950s. Needless to say, it needed a lot of work. Before he actually paid for it, Michael asked me if I would help him fix it, and I said sure. It looked like it would be a lot of fun to get it running again.

The first thing that I advised him to do-once he got the machine home-was to buy a digital multimeter. With the digital multimeter, he was able to:

  • Check the voltage across the transformer secondary windings to ensure that the transformer was still good.
  • Check the continuity of the many solenoids in the machine to ensure that they were not shorted or open.
  • Check the switches to make sure that they operated properly.
  • Check the continuity of the wires in the cables connecting all the switches, solenoids, and indicators.
  • And make many other measurements.

Without the digital multimeter, it would have been next to impossible to get the machine working again.

If you’re an amateur radio operator, you’ll need a multimeter to measure the output of your power supply and set it properly. You’ll need it to measure the resistance of the resistor that you’re going to insert in the printed circuit board of the kit you’re building. You’re going to need it to make sure that you haven’t shorted out your coax after you’ve installed a PL-259 connector on it. I have used mine for all of these measurements and more.

If you’re a homeowner, you can use a multimeter to check that the voltage present at an AC wall socket is really 117 VAC. You can also use it to make sure that the socket is wired properly.  You can also use it to tell if a switch is working properly or if a circuit is wired properly.

What is a digital multimeter?
Simply put, a DMM is a test instrument that allows the user to measure voltage, current, and resistance, the three primary characteristics of an electrical circuit. While some DMMs may have other functions, measuring voltage–both direct current (DC) voltage and alternating current (AC) voltage, AC and DC current, and resistance are the most basic.

It’s called a “digital” multimeter because it uses digital electronics technology, rather than analog electronics technology to make measurements. Older “analog” multimeters used an electro-mechanical meter, like the one shown below, to indicate the value of the voltage, current, or resistance being measured. To make the measurement, you had to note how far the meter’s needle had deflected and then read the value from a scale printed on the face of the meter. A digital multimeter, on the other hand, displays a number on its LCD or LED display.

The venerable Simpson 260 analog multimeter uses an electromechanical meter to read out measured values

The venerable Simpson 260 analog multimeter uses an electromechanical meter to read out measured values

The difference between the two technologies is very similar to the difference between mechanical clocks and digital clocks. With a mechanical clock or watch, you have to note the positions of the two hands and then estimate the actual time. With a digital clock, you simply read the numbers. Both tell you the time, though.

While many old-timers swear by their analog meters, and while there are a few applications for which an analog meter is preferable to a digital meter, if you’re in the market for a multimeter, you want to buy a digital one. One reason for this is that most analog meters—at least ones that are any good—are really expensive. This generally makes instruments made with an analog meter more expensive than a digital multimeter that offers similar performance.

A digital multimeter will open up the world of electricity and electronics to you. With a digital multimeter, you’ll be able to make measurements that will show you how electrical and electronic circuits really work. And with that knowledge, you’ll save money as a homeowner and have more fun as an electronics hobbyist.

From the trade magazines, selecting crystals, understanding measurement uncertainty, Maxwell’s equations

Another selection of articles from the electronics engineering trade magazines……Dan

Selecting Crystals For Stable Oscillators
Understanding how quartz-crystal resonators operate can lead to designing crystal oscillators with improved stability and better noise performance.

Tutorial on Maxwell’s Equations
There’s a lot of math here, but cracking Maxwell’s equations will give you a lot of insight on how radio works. Registration required.

Understand Uncertainty For Better Test Accuracy
How sure are you of that measurement you just made with your multimeter or wattmeter? This article might open your eyes as to the accuracy of your measurements.