Monthly Archives: March 2018

Science Fair Project: Magnetic Lines of Force

If you’re reading this page because Junior just remembered that the science fair project needs to be handed in tomorrow, there’s no need to panic! This site is full of interesting science fair projects. Some of those projects might take some time to complete, but many of them can be whipped into shape in an evening. This one falls into that category. Junior can make an impressive display by mapping magnetic lines of force.

If the project is due tomorrow, have Junior start reading the Wikipedia article about magnetic lines of force. In the meantime, you can race to the hardware store or dollar store to get the items he’ll need, if you don’t have them already.

First, you’ll need some insulated wire. Any kind of wire will work, as long as it’s insulated. At the dollar store, you can probably find it in the electronics aisle in the form of speaker wire. Get about 10-20 feet.

You’ll also need a battery. The old-fashioned dry cells shown above look nice, but there’s really no need. Normal D-cell flashlight batteries will work just fine. Get a few extras, since they will be used up quickly.

Finally, you’ll need a cheap compass. If you don’t have one already, you can probably find one in the toy department, and it will work fine. And while you’re there, don’t forget to get the obligatory poster board, markers, etc.

Have junior construct the loop of wire shown in the picture, and embed it in a piece of cardboard. Hook the ends of the wire to the battery, and you have created an electromagnet. Simply move the compass around the cardboard, and with a pencil, make a small mark showing what direction the compass is pointing. Connect all of these marks, and you will have an accurate diagram of the magnetic lines of force.

The teacher will be impressed, Junior will get a blue ribbon, and nobody will know that he waited until the last minute.

You can find more details in the March 1943 issue of Popular Science, from which the illustration was taken.

1943 Test Equipment

One item that was in short supply 75 years ago were meter movements. There was a backlog in their manufacture to the point where hams were being encouraged to sell their old ones, as shown from the form at left from the April 1942 issue of QST.

But the absence of a meter didn’t have to mean that it was impossible to measure things. The device shown above was a simple bridge circuit for measuring the values of resistors, capacitors, and inductors. The circuit was contained in an article in the March 1943 issue of QST, submitted by W.J. Mertz, VE4UN, using whatever was available. An audio signal is fed into the input, and the potentiometer adusted until the circuit is in balance, at which point the audio output disappears. By calibrating the dial with a few known values, the unknown value can be quickly determined.

The author didn’t have an audio oscillator, so he instead used the device by feeding in the squeal from a regenerative receiver. And in the absence of anything else to make the dial pointer, he used the handle of a broken toothbrush.

While inexpensive multimeters such as the one shown at the left make this project less necessary today, it could serve as the basis for an interesting science fair project for relatively advanced students. For information about the theory involved, a trip to Wikipedia will provide the necessary background.

1928 Power Supply With Homemade Rectifiers

Tired of the bother and expense of having to buy batteries for his radio, the gentleman shown here is taking matters into his own hands by constructing a B-battery eliminator, following the plans in the March 1928 issue of Popular Mechanics. We showed a 1926 version earlier, and this one is more refined.

In this case, hum is dealt with by electrolytic capacitors, which were available for purchase. Rectifiers, on the other hand, weren’t as easy to come by. But undaunted, he just made his own, consisting of plates of lead and aluminum carefully suspended in pickle jars containing an electrolyte solution. That solution could be borax, sodium bicarbonate, or ammonium phosphate.

The rectifiers were just a bit tricky to get going, which explains the light bulb in series with the transformer primary. If the rectifiers were doing their job, the lamp would light briefly and then dim. If the light remained on, it meant that one of the cells needed attention. In either case, the light bulb served to limit the current and protect the expensive transformer.

Since modern rectifiers are so inexpensive, there’s little practical reason to make your own. However, they’re so simple to construct that a homemade rectifier would probably be the basis of an excellent science fair project for the advanced student.

1938 Admiral Model 55 Car Radio

Eighty years ago this month, the March 1938 issue of Radio Today carried this ad for the Admiral Model 55 Auto Radio. The 5 tube superheterodyne featured five preset buttons. Unlike earlier models in which each button contained a tuned circuit, in this one, pushing the button moved the main tuning dial.

Some competing Delco models from three years later are shown below, from the 1941 catalog we showed a few days ago.

1968 One Tube Transmitter

Fifty years ago this month, the March 1968 issue of Electronics Illustrated showed how to put together this transmitter for 40 and 80 meters. As the photo makes clear, it’s about as simple as can be.

It uses a 50C5 (or 50L6) tube, with the filament powered directly off the AC line with a 400 ohm resistor. Two silicon rectifiers are used as a voltage doubler to provide about 350 volts for th plate.

All components are mounted on a wooden board, with connections soldered to finishing nails on the board.

The neon lamp in the schematic is there as a safety precaution. Since one side of the key is connected directly to the power cord, the lamp comes on to show that it’s plugged in the wrong way–with the hot side on the key. If you plug it in and the light comes on, then you should reverse the plug. (And you’ll probably have the added complication of blowing the ground fault interrupter of modern house wiring.)

Also, since there’s no filtering of the output, this transmitter probably doesn’t meet modern spectral purity requirements.

1977 Soviet Youth Telegraph, With Bonus Machine Gun & Radio

At first glance, this appears to be an American Boy Scout working on his signaling. But it’s not. It’s actually his Soviet counterpart, a Young Pioneer getting the message through. The image is from the cover of a 1977 issue of Masterok magazine, a Soviet journal designed to instill in middle school age children the necessary skills for labor education.

This issue seems to focus on communications skills, and for the beginners, it describes how to make this tin-can telephone, albeit a rather advanced version of the old staple:

It moves next to Morse signaling, showing how to make this buzzer set:

Of course, the young comrades need something to communicate about, so the magazine shows them how to make this realistic looking machine gun, perfect for taking out invading capitalist imperialists:

After all that excitement in the field, the Pioneers can relax by listening to the radio after building this three-transistor TRF set. It employs permeability tuning, one stage of RF amplification, and two audio stages for good headphone volume.

Answers to Yesterday’s Puzzle

Yesterday, we showed this picture from the March 1943 issue of Popular Science of a radio with eight things wrong with it. As promised, here’s what’s wrong:

ARRL Petition for Technician Digital & Voice HF Privileges

The ARRL recently made a Petition for Rulemaking with the FCC. The request boils down to giving Technician class licensees some phone and digital privileges on 80, 40, and 15 meters.

I think this is long overdue, since it will allow Technicians, holders of what is now the entry-level license in Amateur Radio, some minimal but meaningful privileges on HF, similar to what I had as a beginner over 40 years ago.

The Entry-Level License in 1974

When I was first licensed, the entry level license was the Novice class. I had to pass a simple multiple-choice test, as well as a simple 5 WPM code test. When I did so at the age of 12, I was allowed meaningful HF privileges. And in my case, it wasn’t until I actually received the privileges that I realized how meaningful they were.

Before I got the license, I realized conceptually that hams could communicate around the world. But I didn’t really believe it. I assumed, incorrectly it turns out, that to really get out, you needed a lot of power and/or a big antenna. I assumed, incorrectly it turns out, that with 75 watts and a wire antenna, I would be able to get out locally, and maybe with good conditions, I might make occasional contacts with the next state. But I didn’t really believe that I would be able to communicate around the country and around the world on a regular basis.

Nobody told me this. In fact, I was told the opposite. But I didn’t quite believe it. I didn’t believe it until I actually got on the air. When I did get on the air, I was soon filling up my log with contacts from all over the United States. Eventually, when I discovered 15 meters, I was getting out all over the world, all with 75 watts and some wire in the air.

What got me licensed in the first place was a somewhat undefined interest in radio and electronics. What got me hooked was the realization of how much fun it was to bounce my radio waves off the ionosphere whenever I wanted. New licensees need the same thing to get hooked today, but it’s not readily available.

The Entry-Level License Today

New hams today don’t have this same opportunity. The entry-level license is now the Technician license, with privileges mostly on VHF. As a practical matter, this means that most of them get an inexpensive handheld such as the Baofeng UV-5R shown here.

There’s nothing inherently wrong with this radio. In fact, for the price, it’s amazing what it will do, and I’ve written about it previously. But this is the opposite of how I got started. I started on HF, and was able to bounce signals off the ionosphere, an activity that greatly exceeded my expectations. From the very first day I was licensed, I was able to interfere with Radio Moscow, and I did! Only after I had upgraded, to either General or Technician, was I able to get on VHF. At the time, that was something of an incentive, because there was a great deal of local repeater activity. Long before the age of cell phones, I was able to communicate with a handheld device, and even make phone calls. But an HT such as this really doesn’t have much capability beyond that of even the cheapest cell phone. It’s hardly an upgrade. In fact, in many areas, 2 meter FM is practically vacant. Repeaters are still up and running, but there are generally only the same handful of local operators day in and day out.

Technicians are also currently allowed to use SSB and data on 10 meters. This is somewhat of an improvement, since this band occasionally opens up to worldwide communications. Unfortunately, it’s not open most of the time. This is very different from my experience as a novice. With just one band, 40 meters, I could talk to someone almost any hour of the day or night. During the day, it would be 500 miles or so. At night, it would be over most of the continent.

Current technicians are also currently allowed to use CW (Morse code) on 80, 40, and 15 meters, and I think they should take advantage of this opportunity. But unfortunately, unlike when I was first licensed, there aren’t too many people willing or able to teach them the code and help them get on the air. And there’s also the question of price, since the cost of a radio for CW (or SSB) is often considerably more than the cost of a digital radio.

Digital Modes for New Licensees

The ARRL’s proposal will allow new licensees to do exactly what I did over 40 years ago: With inexpensive equipment, they would be able to get on the air immediately with digital signals on the lower HF bands. They would be immediately bouncing signals off the ionosphere, just like I did 40 years ago.

This can currently be done with equipment that costs about $125, assuming that they already own a computer, tablet, or smartphone. If there was a demand for the product, there would be other models available, probably at a lower price, and it would also be possible for them to make it in a group-build of a kit project.

UT5JCW Digital Transceiver.

Currently, the only standalone digital rig available are a set of transceivers produced by UT5JCW in Ukraine. They plug directly into a computer, and can be used for all digital modes, including JT65, FT8, and PSK31. They require only a simple antenna, which could be as simple as a quarter-wave piece of wire strung in the backyard. For 40 meters, the band I would recommend for a beginner, this would be 33 feet long.

With a radio such as this one, a new ham could be on the air almost immediately, making meaningful contacts all around the country. It would be a much more meaningful introduction to ham radio than simply talking with the same handful of locals on a 2 meter repeater.

And the cost could be very comparable. As noted above, the only radio currently on the market costs $125 shipped from Ukraine. But this hasn’t always been the case. Until several years ago, a kit called the PSK Warbler was available in kit form for about $40. With guidance (perhaps as part of a licensing class), construction of such a kit was within the expertise of even a beginner.

I think that there could be a very meaningful introduction to ham radio if beginners were able to get their license and start out right away with a radio such as this one. It would be more or less the functional equivalent of how I got started on 40 meter CW 40 years ago.

Is Today’s Test Really Easier?

One argument against changing the rules is that the test has allegedly been “dumbed down” over the years, and that beginners should not be given HF privileges until they have taken a test that is sufficiently difficult.

However, this argument is based on a false premise. When I took the test for the entry-level test in early 1974 at the age of 12, it was much easier than the current Technician exam. I had to take a 20 question multiple choice test. That test was very easy: I had to memorize the meaning of some new vocabulary words (such as “pecuniary”). I had to learn some pieces of trivia. For example, I had to know that transistors were made out of silicone and geranium. (Actually, it turns out that it’s silicon and germanium, but that was close enough.)

Transistor raw materials. USDA photo.

I had to memorize a few equations, such as Ohm’s law. I didn’t need to understand what was going on. I needed to know, for example, that if the question included the words “Volts” and “Ohms”, then I needed to divide Volts by Ohms, and that was the right answer. I also had to memorize the formula for the length of a dipole antenna, 468/f.

I was well aware that there was going to be one complicated word problem on the test. This appears as question number 46 below, which called for me to calculate the input power to a final amplifier stage. I knew to an absolute certainty that this question was going to be on the test, and it was there, more or less verbatim. The only thing that changed was the actual numbers. I had to ignore the filament numbers. Like any word problem, irrelevant information was included. I had to multiply screen voltage and screen current, and then multiply plate voltage times plate current. Then, I added up those numbers, and also added drive power. And sure enough, when I did this, even if I didn’t really understand what was going on, that number was one of the multiple-choice answers.

To give some idea of how easy the novice test was, I scanned the novice questions and answers from the 1975 license manual. By simply reading these six pages, and making sure that some critical facts were memorized, it was almost certain that anyone attempting the test could pass with flying colors, even if, like me, they didn’t really understand most of the material.

Here are those six pages from the 1975 license manual. These questions might have changed slightly from when I took it in 1974, but they are almost identical. (To download these pages to your computer as a PDF file, use this link.)

As you can see, there are a couple of questions in the study guide asking you to draw a particular circuit. However, the exam was strictly multiple choice, and it was known in advance that it was multiple choice. So there might have been a question with the drawing asking to name a part, or identify a missing part. But I didn’t have to draw any diagrams, and I knew going in that I wouldn’t have to.

Basically, just about anyone could have passed the Novice license test 40 years ago after reading these six pages. I’m the author of a study guide for the current Technician exam, and I use 160 pages to explain the material. Yes, I probably go into a bit more detail than the License Manual did 40 years ago, but I didn’t include much excess details. Based upon my familiarity with both exams, I would say that the test I took was a lot easier, yet it gave me the opportunity to interfere with Radio Moscow.

In other words, it’s simply not true that the entry-level license test today is easier than it was 40 years ago. It’s not much more difficult, but I was never required to take a difficult test before getting on HF. There’s no reason why the same thing shouldn’t be true today.

What’s Wrong With This 1943 Radio?

This puzzle comes from the March 1943 issue of Popular Science.

The picture shows a four-tube AC-DC TRF receiver. But there are eight things wrong with the picture. A few are obvious, and a few you’ll be able to spot with a little bit of thought. If you can spot all eight, then you can consider yourself an expert on vintange radio.

The answers will appear tomorrow.

1918 Boys’ Life Looks at Wireless

A hundred years ago this month, the March 1918 issue of Boys’ Life magazine included this article by F.A. Collins (probably Archie Frederick Collins) about the state of radio, especially as it related to war. He starts by explaining that “the thing that was impossible yesterday, today is indispensable in commerce and war, wireless telegraphy.”

And he makes clear that the radio section of the Signal Corps was something especially within the grasp of scouts:

Probably no country in the world can recruit men for this exciting service in such numbers as the United States. There are already tens of thousands of boys throughout the country who have had valuable training as amateurs. It has been estimated that this army of amateurs exceeded over 100,000 boys and girls. Thousands of Boy Scouts, for example, have an excellent working knowledge of wireless and have learned to transmit at a rate of twenty words a minute or faster. The Government does not accept operators under eighteen years of age and many of these boys are practical wireless operators by the time they reach this age ready to enlist in this interesting branch of service.

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