Eighty years ago this month, the March 1939 issue of Radio Craft carried the story of Edward J. Winterding, Jr., of Cleveland. The 21 year old man had been hospitalized for 18 months for some unstated reason. But during that time, he sold nine radios and appliances to hospital staff and other patients.
Seventy-five years ago this month, the March 1944 issue of Radio News reminded readers that they could use a broadcast radio to make sure their 100 kHz crystal calibrator was in tune.
Before the days of digital readouts, you needed to know what frequency you were tuned to. The easiest way to do this was with a crystal calibrator, an oscillator putting out a signal on (usually) 100 kHz. To calibrate your receiver, you would switch on the crystal calibrator, and you would hear the harmonic every 100 kHz up the dial.
To make sure the calibrator was in tune, you could use the method described in this article. You would hook the calibrator up to your broadcast receiver, and then zero-beat it with a broadcast station on a frequency divisible by 100. The article included a list of the 108 stations in the U.S. that met that description. (The article noted that 83 of those stations were on 1400 kHz.
The article noted that FCC rules required broadcast stations to be within 20 cycles of their assigned frequency, although most were closer. It also suggested that a phone call to the station might get a more exact answer as to how close they were at that moment.
Seventy years ago this month, the March 1949 issue of Radio Electronics magazine carried this depiction of the state of television in the United States.
According to the magazine, in the previous year, TV was rampaging across the nation. While a year earlier it had been confined to a handful of cities, it now had a foothold nationwide. 46 million Americans were within range of a station, and the magazine predicted that an additional 25 million would have access before the year was over.
If you’re looking for a really dangerous science experiment, then you need look no further than the March 1969 issue of Popular Electronics. The magazine describes the electret. It points out that it is the analogue of a permanent magnet. Instead of producing a permanent magnetic field, the electret produces a permanent static electric field. For example, it’s possible to make an electret, and then use it to produce a spark weeks, months, or even years later. The name electret was coined by Oliver Heaviside in 1885 as a combination of electr- from electricity, and -et from magnet.
The process to create an electret is quite simple. You simply take a suitable material (in this case, a piece of lucite), heat it to a high temperature, and then let it cool while applying a high voltage. That sounds easy enough, but the voltage must be very high. The article suggests 14,000 volts, and tells you exactly where you can get it–from the family’s portable TV set.
You simply remove the anode clip from the picture tube, and that’s your source of high voltage. But as the article rightly points out, messing around with 14,000 volts could easily prove fatal if you make the smallest mistake. So we don’t recommend this particular experiment. Old TV sets had an interlock for a reason, and that was to prevent them from operating when the case was open. In fact, as the article points out, the wire in question could easily deliver a deadly jolt even with the set unplugged and turned off. This is because the capacitors in the power supply retain a charge. In other words, you probably shouldn’t attempt to duplicate this experiment unless you are very familiar with exactly what the dangers are.
But the procedure itself is quite simple. You build an oven a shown here, and use Sterno to heat it. When you reach the desired temperature, you carefully wire up the high voltage. While standing back many feet, you plug in the TV. If you hear strange noises, then you unplug the TV. Prior to making the connection, and after you unplug the set, you need to discharge the TV’s power supply capacitor. The article recommends an electrician’s glove.
After the lucite is fully cooled, you disconnect things, and you have yourself an electret.
Of course, modern televisions don’t have CRT’s, so they don’t have 14,000 volt power supplies inside. So if you’re intent on duplicating this experiment, you’ll need to find an old TV, the older the better. Even though we have this experiment in the “science fair ideas” category, we don’t recommend it to students due to the lethal voltages involved. But we have many other experiments that you can find by browsing that category.
Alexander Stepanovich Popov. Wikipedia photo.
Today marks the 160th birthday of Alexander Stepanovich Popov, born on March 16, 1859, in Krasnoturinsk, Sverdlovsk Oblast, Russia. He is regarded in Russia and much of Eastern Europe as the inventor of radio. He improved the coherer to the point where it could receive radiotelegraph signals at a reasonable speed. In 1895, he employed the improved coherer as part of a lightning detector. On March 24, 1896, he used radio to transmit a message between university buildings in St. Petersburg.
1989 Soviet stamp showing Povov demonstrating first radio, 1895, Wikipedia image.
Yesterday, we carried a quiz from the March 1969 issue of Popular Electronics. Here are the answers and explanations.
Fifty years ago this month, the March 1969 issue of Popular Electronics carried this quiz on Ohm’s law. A few of the questions have some tricky aspect that you might need to notice, but they can all be solved with the familiar E=IR equation.
Answers will appear here tomorrow.
Seventy-five years ago this month, the March 1944 issue of Radio Craft magazine contained this interesting idea for using a burnt out fluorescent tube as a radio detector. Even though the filament is open, current can still flow from one end to the other through the ionized gas, and apparently it can rectify.
The magazine also showed how the tube could be used as an audio oscillator, as shown in the diagram below.
Even though there were wartime parts shortages, the experimenter could probably get his hands on a burnt out lamp.
Shown here are students at South Side High School in Rockville Centre, New York. During the club’s two year history, fifteen members had obtained FCC licenses. This included three girls, and the majority of the current class studying code were also girls.
The club station call sign was K2LAK, and was under the direction of the school’s industrial arts director, Miles Stireman, K2KAT. Shown at left at the National NC-300 and Johnson Valiant are members Diane Anhel, KN2LLB, and Ed Davis, K2PHK.
The photos appeared in the March 1959 issue of Electronics Illustrated.
Eighty years ago this month, the March 1939 issue of Radio Retailing magazine carried this ad for an interesting looking mobile shortwave converter.
From ABC Radio Laboratories of 3334 N. New Jersety St., Indianapolis, IN, the Model 600 covered the 49-16 meter bands. It noted that the unit was “especially adapted to use in tropical countries and the more remote parts of the world.” The set retailed for $24.95.
Also shown was a converter that tuned 1500-2600 kHz to pull in police calls “for use of police and other law enforcement officers.”
The unit is a bit reminiscent of the Gonset shortwave converter, which came out in the late 1940’s. I actually had one of the Gonsets installed in a vehicle in the late 1970’s, and it was a fairly sensitive receiver until one day when the magic smoke leaked out. Since the solid-state car radio wasn’t capable of supplying B+, I used a separate vibrator power supply.