How do you know that fuse is protecting your circuit?

How do you know that this fuse will protect your rig?

How do you know that this fuse will protect your rig?

I blog for a leading manufacturer of circuit protection devices, so I keep my eye out for articles on fuses, ESD diodes and the like. Recently, I came across the article, “Fuse selection factors critical to circuit design.” Among the factors discussed is:

11. Application testing/verification prior to production.
Request samples for testing in the actual circuit to verify the selection. Before evaluating the samples, make sure the fuse is properly mounted with good electrical connections, using adequately sized wires or traces. The testing should include life tests under normal conditions and overload tests under fault conditions to ensure that the fuse will operate properly in the circuit.

Being a former test engineer, this got me to thinking about how one would actually do this. For example, how would you test that a fuse will actually protect a circuit board? Would you inject faults, i.e. deliberately short-circuit nodes? If so, which ones?

What measurements would you make to ensure that the fuse was working as you hope? Would you measure the time elapsed between the time you injected the fault until the time the fused actually blew? How about measuring the current profile over that period of time? That might be important and/or tell you something about the failure.

What kind of fault analysis should you perform after the fuse has blown? I suppose at the very least you’d want to replace the fuse and ensure that the circuit is functioning again. I would say that you should also run a full performance test to ensure that the fault didn’t adversely affect the board’s performance. Also, I’d think that you’d want to visually inspect the board to ensure that the fault current didn’t damage the board or traces at all.

I’m curious if any of you have had any experience with this kind of development testing. If so, please e-mail me or comment here.

Is Getting an Extra Class License Really All That Extra?

On the HamRadioHelpGroup mailing list, there is a discussion on the relevance of some of the questions on the Extra Class license exam and how easy it is to pass the exam by memorizing the answers. Here is my response:

Whether or not you use what you learn while studying for the Extra Class license is immaterial. An Extra Class license holder is supposed to know about all aspects of amateur radio, and in some depth. That’s the whole idea of the Extra Class license.

Furthermore, you’ll be surprised when that knowledge comes in handy. I liken it to the courses I took in engineering school. As an electrical engineering student, I questioned the need to take thermodynamics and fluids courses. Well, that knowledge certainly came in handy when I became a project manager responsible for the design of an electronics control system. It helped me understand how airflow helped keep the electronics cool as well as the algorithms the controller used to control fluid flow in the field.

Something similar could be said about amateur radio. At this point, I have no desire to work satellites. That doesn’t mean that I won’t get interested in doing so at some point in the future. By having read a little bit about it to answer some questions on the Extra Class exam, I’m that much closer to actually doing it.

Finally, let me say a few words about passing the test by memorizing the answers. First of all, doing that is not all that easy for the Extra Class test. There are, after all, more than 500 questions in the question pool. And, to answer many of the questions correctly, you have to memorize the answer. There’s no way to learn the theory.

An example of this is question E2B21. The question is, “If 100 IRE units correspond to the most-white level in the NTSC standard video format, what is the level of the most-black signal?” The answer is 7.5 IRE units. To get that question right, you just have to memorize the answer.

Second, I don’t think many people can go through that memorization process without learning something. I have a friend who always claims that he passed the Extra test by memorizing all of the answers. He’s just playing dumb, though. He knows a lot more than he gives himself credit for, and I think that you’ll find the same thing is true for the clods who claim to have passed by simply memorizing the answers.

Third, even if someone could pass the test simply by memorizing the answers, they’re only cheating themselves. Why spend all that time and energy just memorizing the answers, when you can actually learn something? Especially when actually learning something will certainly prove useful in the future and make ham radio that much more fun?

Is the test material too easy? Perhaps. You have to remember, though, that this is just a hobby. We’re not talking about the installation and maintenance of systems with life-or-death consequences, such as air-traffic control systems or medical electronics.

If after thinking about all this you still think that the test is too easy, get on the committee that makes up the question pool. The question pool is drafted by a committee of Volunteer Examiners. They welcome your input.

I’m Now a VE

A little over a month ago I decided to bite the bullet and get my VE certification. It wasn’t difficult to become ARRL-certified. You simply get the VE Manual (free download), read through it, then take an open-book test (the ARRL calls it an “open-book review”). It took me about an hour and a half to complete the “review.”

You then e-mail, fax, or snail mail the forms to the ARRL. Jim, K8ELR, who also recently applied for his certification, got his in three weeks. It took them almost five weeks to process my application. They send you the nice certificate (shown above) and a badge identifying you as a VE.

One reason I wanted to be certified is to help out with the testing of my One-Day Tech Class students. I’m also thinking of setting up a Laurel VEC team. The Laurel teams don’t charge a dime for the test. Finally, being an “official” VE allows me to participate more directly in the question-pool development process.

Contest Aims to Measure Interference Caused by Home-Networking Devices

The Electromagnetic Compatibility Industry Association (EMCIA) is a British trade group comprising “companies involved in supplying, designing, testing and manufacturing EMC products.” The EMCIA has been a big critic of BPL in the U.K.

They recently announced a contest to identify the interference range of Power Line Telecommunications – otherwise known as PLC or BPL. These devices aren’t BPL devices as we know them here in the U.S., but rather home networking devices that use a home’s power wiring to network computer devices.

The objectives of the contest are:

  • To conduct EMC testing of Power-Line Adaptors in their installed configuration at a statistically-significant number of sites so as to help determine interference probability as defined in CISPR16-4-1; 2003.
  • To provide EMC test data from a single emission source that is relevant both to such a single source and by extrapolation to the cumulative effect of many such sources, so as to facilitate the analysis and presentation of information about the interference probability of installations of PLT equipment. (PLT is elsewhere known as PLC or BPL).

The contest rules also includes this statement: “For the convenient measurement of interference emission without the use of laboratory-grade equipment these objectives are to be met by exploration of the distance of detection of the interference emissions from a single installation of Power Line Adaptors (PLAs).

This is a strictly UK contest. The rules say that the devices under test must be available to the UK consumer, and they must be installed in a UK residence. That being the case, I hope some of our UK brethren accept the challenge and do a bang-up job on it.

Ham Radio IS NOT a Dying Hobby

I really hate it when people ask me, “Ham radio? Do people still do that?” Yes, of course, we still do that. Not only that, ham radio is growing. Below, is the latest press release from the ARRL. Now, granted, this release does hype up the statistics, but the facts are there. Almost double the number of new licenses were issued in 2009 than in 2005, and there are now almost 700,000 licensed radio amateurs in the U.S.

2009 Sees Surge of New Amateur Radio Licensees

Newington, Conn., Jan 7, 2010 – 2009 was a banner year for new people getting Amateur Radio licensees in the US. Amateur Radio, often called “ham radio,” has been growing over recent years, but 2009 was a record. According to the ARRL, the national association for Amateur Radio, the FCC issued more than 30,000 new ham radio licenses in 2009.

A total of 30,144 new licenses were granted in 2009, an increase of almost 7.5 percent from 2008. In 2005, 16,368 new hams joined Amateur Radio’s ranks; just five years later, that number had increased by almost 14,000 — a whopping 84 percent! The ARRL is the largest of several organizations trusted by the FCC to administer Amateur Radio license exams in the US.

“When looking at the statistics over the last 10 years, these are some the highest numbers we’ve seen,” explained Maria Somma, manager of the ARRL testing programs. “The total number of US amateurs has grown each year.” Currently there are 682,500 licensed Amateur Radio operators in the USA, an almost 3 percent rise over 2008. In 2008, there were 663,500 licensed amateurs; there were 655,800 in 2007. There are approximately 2.5 million Amateur Radio enthusiasts worldwide. It was also noted that a much higher percentage of licensees are going far beyond an entry-level license and earning higher class (and much more difficult) FCC Amateur Radio licenses. Despite the predictions of some commentators that Amateur Radio would be dying with the development of cell phones and the Internet, hams instead have taken and incorporated those digital and computer technologies into their wireless hobby, creating many new developments in the process.

Somma applauded all the volunteers whose “hard work and contribution of countless hours of time helps to ensure the future of Amateur Radio. I am delighted by these important achievements. 2009 was a very good year for Amateur Radio and I am excited by the promise of 2010.” For more information see

New Tech Question Pool Released


NCVECNCVEC Releases New Technician Class Question Pool (Jan 4, 2010) — The Question Pool Committee (QPC) of the National Conference of Volunteer Examiner Coordinators (NCVEC) released the new Technician class (Element 2) question pool on Monday, January 4. This new question pool will become effective for all examinations administered on or after July 1, 2010; it will remain valid until June 30, 2014. The current Technician question pool that became effective July 1, 2006 will expire June 30, 2010. The new Technician pool contains approximately 400 questions, from which 35 are selected for an Element 2 examination; it will contain graphics and diagrams, something new for this element. The current General class question pool was effective July 1, 2007 and is valid through June 30, 2011. The current Amateur Extra class pool was effective July 1, 2008 and is valid until June 30, 2012.

There are 392 questions in the current pool, so there aren’t that many additional questions, but there are some diagrams in this pool, which is a change. My first impression is that they’ve made this pool a little more technical than the previous pool, which is probably a good thing.

Now it’s time to update my study guide. I’ll know more once I’ve done this.

Passing the Tech Test

As many of you know, I teach One-Day Tech classes. At the start of each class, I go over the following to help focus students on what to keep in mind when taking the test.

Technical Topics
For the Tech test, the focus is on rules and safety. It is not very technical. Having said that, there are three technical topics that you need to know:

  • Ohm’s Law,
  • how to calculate power, and
  • the relationship between frequency and wavelength.

Ohm’s Law
The basic formula for Ohm’s Law is voltage (E) equals current (I) times resistance (R), or E = I x R. On the test, there are several questions where they give you two of the values and ask you to calculate the third. If you’re asked to calculate the current, you use the formula, I = E / R. If you need to calculate the resistance, use the formula R = E / I.

How to Calculate Power
The formula for calculating power is power (P) = voltage (E) times current (I), or P = E x I. To calculate the current drawn, when given the power being consumed and the voltage applied to the circuit, use the formula I = P / E.

Relationship Between Frequency and Wavelength
There are several questions that require you to calculate the wavelength of a signal or some fraction of the wavelength. The reason for this is that antennas are often a fraction of a wavelength.

The formula that describes the relationship between frequency and wavelenght is wavelength in meters = 300 / frequency in MHz. One question asks for the approximate length of a quarter-wavelength vertical antenna for 146 MHz. To figure that out, you first calculate the wavelength:

wavelength = 300/146 = 2.05 m or about 80 inches

One quarter of 80 inches is 20 inches, and the antenna will actually be a little bit shorter than that because radio travels more slowly in wire than it does in free space. The correct answer to this question is 19 inches.

That’s all there is to the technical part of the test!

There are lots of questions on the test about operating safely and being safe when working on antennas. My advice when answering these questions is to always choose the most conservative answer. The two exceptions are when asked what is the lowest voltage and current that can hurt you. For these questions, the correct answer is the second lowest choices.

There are lots of questions about what to do in emergencies. There are two things to keep in mind when answering these questions:

  • You should do whatever you can to help someone who is in an emergency situation.
  • You can even break the rules to help someone in an emergency situation. This includes operating on frequencies you are normally not allowed to operate on and communicating with other stations in other radio services.

Miscellaneous Tips
Here are a couple of other miscellaneous tips:

  • The answer is ‘D.’ If one of the answers to a question is, “D. All of these answers are correct,” chances are that is the correct answer. There are 18 questions with this option, and of those 18 questions, there are only two questions–T3B06 and T5B03–where that is not the correct answer.
  • Long-Answer Rule. Where one answer is a lot longer than the other options, chances are that this is the correct answer. I haven’t done an exhaustive study of this, but when one answer is very long, take a good, hard look at it.

That’s all I have. What tips do you have for passing the Tech test?