Eighty years ago today, the April 21, 1941, issue of Life magazine carried this ad from General Electric reminding readers such as this businessman and his efficient secretary that his desk would be an excellent spot for a radio, for keeping up with news and stock reports affecting his business.

Their suggestion was the model L-500, which sold for only $9.95 (according to this inflation calculator, $162.17 in 2021 dollars).  The  “All American Five” set had the then-standard tube lineup of  12SA7, 12B7, 12SQ7, 50L6GT, and 35Z5GT.  According to the ad, the set had excellent tone. We previously featured the L-500 at this link.

The ad also featured the portable model LB-502, a five tube ( 1R5 1T4 1S5 3S4 35Z3) camera-style portable that would run from either batteries (1.5 and 67.5 volts) or household current.  It carried a list price of $21.95, or almost $400 in today’s money.

The September 1951 issue of Popular Mechanics showed how to put together this simple two-tube receiver. It was earmarked especially for the new ham, since it covered the 80 meter ham band. But it would also pull in a wider range of frequencies, including police calls and the 49 meter international broadcast band.

The timing of the article wasn’t a coincidence, since the circuit was specifically targeted at those interested in the Novice class amateur radio license. That new license, which required only a 5 word per minute code test, had just been announced by the FCC, which started issuing them on July 1, 1951. Armed with this receiver, and a key and buzzer, the prospective Novice would be able to pass the test with ease. The magazine promised that the October issue would include an accompanying transmitter.

Construction was simple, as it used two pieces of hardwood mounted on wooden cleats. There was a gap between the two boards, allowing for easy mounting of the sockets for the two tubes and one plug-in coil. Power came from a 45 volt battery, but to prevent having to replace A batteries, a 6.3 volt transformer was used to light the filaments. No power switch was provided, and the magazine noted that a switch could be mounted somewhere on the operating table in line with the transformer.

The magazine recommended a 10-15 foot indoor antenna and ground for the two-tube regenerative set. One variable capacitor was used to control regeneration, with another one serving as the main tuning dial. The procedure for using the set was to advance the regeneration until the set came to life, and then tune the main tuning dial until 80 meter stations were heard. At that point, the larger bandspread dial would be used for tuning.

Eighty years ago this month, the April 1941 issue of Popular Science showed this novel little one-tube receiver. Even though it’s basically a crystal set, it qualifies as a one-tube radio since it uses a rectifier tube, a 25Z5, in place of the crystal.

The article points out two things that might not be obvious. First of all, even though the set is running on AC power, there is no hint of 60 cycle hum. The electric power does nothing but heat the filament, and the heated cathode and plate serve as the detector, with no electrical connection to the power. The magazine also notes that it’s safe to use a ground connection, since there’s no direct connection.

Even though the filament normally runs on 25 volts, it should be under 6 volts in this circuit. An 80 watt resistor is used to drop the voltage, although I bet an incandescent light bulb could be used.

Fifty years ago this month, the April 1971 issue of 73 Magazine was a special issue devoted to FM repeaters. The cover shows Murry Sessions, the daughter of Managing Editor Ken Sessions, K6MVH, at the mike of a Drake TR-22, a one-watt portable 2 meter FM rig with six crystal-controlled channels. According to a review in the magazine, the set retailed for $199.95.

Of particular interest is the nationwide repeater directory, which took up seven pages in the magazine. The 30 kHz channel spacing had been widely adopted, with some channels designated for wideband and others for narrowband. However, there was no uniformity as to repeater inputs and outputs. 146.34 MHz was a very common repeater input, and 146.94 was a common output, but they weren’t necessarily paired. For example, many repeaters were 146.34 input and 146.76 or 146.88 output. In many cases, frequencies were shared in the same area, with different audible burst tones at the start of the transmission.

This makes sense, since crystals were expensive, and using the same frequency for two repeaters would have allowed users to save having to buy an additional crystal. When I got on 2 meters in the mid-1970s, the most common repeater pair was 146.34/146.94 (although this was not used in the Minneapolis-St. Paul area). However, 146.94 was the most widely used simplex channel. My first two meter rig had crystals for .34/.94, but also had a transmit crystal for .94.

In the 1971 listing, Minneapolis had a repeater with an output of 146.46. The “priority input” was 146.34, with a “courtesy input” of 146.94. The magazine noted that this system was in operation 24 hours. Many systems had limited operational hours. The Minneapolis system also had an input on 6 meters, 53.64 MHz.

Two meter FM saw great growth in the following years, fueled partly by the availability of autopatches to allow phone calls to be made from a mobile or portable radio.  This continued through the 1970s and 1980s, but waned considerably with the rise of the cell phone.  My first two meter radio was a semi-homebrew portable unit with four channels.  Around 1976 or so, I bought a Drake TR-22C, the twelve-channel updated version of the one shown above.  It was loaded with crystals for popular repeater pairs, which had by then been standardized.  Therefore, almost anywhere I travelled with the radio, I was probably within range of a repeater, and it was almost always possible to raise a fellow ham.

Fifty years ago this month, this young comrade was able to help feed his family by locating a school of fish. He managed this by seeking out the perfect water temperature, thanks to an electronic thermometer he constructed himself.

The plans for the project were contained in the April 1971 issue of Юный техник (Young Technician) magazine, which also contained the plans for making the raft, shown at left. It included a number of other circuits, including the one transistor regenerative radio receiver shown below.

It’s likely that the readership of Radio News a hundred years ago was mostly young men who had been bitten by the radio bug.  The April 1921 issue carried this article entreating them to get their friends interested in the hobby. It pointed out that there were “many bright boys and young men who are spending their evenings in idleness or bad company simply because they haven’t found an interesting hobby.” The ideal hobby, of course, was amateur radio, and it was one that would lead to a big future for those who got in on the ground floor with a thorough practical knowledge of radio.

But there was more: “boys, there is an additional reason for getting interested in radio. The ‘reason’ being shown in the accompanying photographs. Some of you fellows may not have known it, but many of the fair sex have gone in for radio and more are taking it up all the time.”

That’s right. Amateur Radio was a veritable chick magnet!  “What could be more interesting than a radiofone conversation during a long, lonesome evening with a sweet-voiced girl on the other end?  Wait until the radiofone becomes more universal and we predict many a romance will be started just this very way.”

The promised photos include, at the lower left, an unidentified girl at her radio set, somewhere in Brooklyn. And at the lower right, a “girl amateur” is receiving some C.W. instruction at the Second District Radio Convention Exhibition.

The picture at the top of the page isn’t, it turns out, just a candid shot of two young women tuning in their crystal set while out for a walk. It’s actually a still from the silent film short feature “Eve’s Wireless“.

The article identifies the actresses as Peggy Brady and Alice Brady of the Ziegfeld Midnight Frolic, a somewhat risque rooftop after-hours presentation after the Ziegfeld Follies let out for the night.

You can view the entire film here:

Sixty years ago, this gentleman, probably Gordon Carlson of the DeVry Technical Institute of Chicago, made the cover of the April 1961 issue of Radio Electronics magazine by mowing his lawn automatically with this fully automatic electronic lawnmower. But this wasn’t a pie-in-the-sky idea concocted by a futurist. Mr. Carlson actually built the thing, and described the electronics in detail in the magazine. Since the mechanical details would vary from lawnmower to lawnmower, he left many of them to the reader. In this case, the automation was added to a Jacobsen Lawn King. But the basic idea was rather simple.

Buried a few inches under the lawn was an insulated wire carrying an alternating current. On front of the mower (shown in the inset in the lower right hand corner of the cover) were two pickup coils, one to the left, and one to the right. When the mower was directly above the wire, the induced currents would be equal, and the mower would proceed straight ahead. But if one current got stronger than the other, the signals would be amplified by the electronic circuit and would trigger a relay which would steer the mower to either the left or the right, using an electric motor coupled to the mower’s steering. To keep the machine from constantly hunting, a further refinement was added. If the mower was only slightly off course, the corrections would be made slowly. But if it got way off track, the steering motor would operate at high speed.

As a nod to safety, a limit switch in front of the mower would cause it to stop if it encountered an obstruction such as a toy, a pet, or a child. As shown in the likely staged photo below, this scheme could apparently be trusted.  I scoured news archives and found no reports of a young woman meeting her demise in a lawnmower accident in that time frame.

No, this device wouldn’t pick up music from the United States Marine Corps, but it would allow your car radio to listen in on the local maritime radio traffic on the 2-3 MHz marine band.

The project appeared in the April 1961 issue of Electronics Illustrated. It used a single 2N140 transistor as an oscillator on 3.5 MHz, when mixed with the 2-3 MHz signals, the output could be heard on the broadcast band. It was powered by a battery which was said to be good for hundreds of hours with the low current drain circuit.

The cost was said to be about $10, which would quickly be paid back with fresh fish. The idea was that by monitoring the traffic from commercial fisherman, the hot fishing spots would be revealed.