Fido is shown here assisting with the construction of this simple one-tube radio from the January 1947 issue of Popular Mechanics. The radio is a very simple regenerative receiver described as a “student set.” The tuning range is 550-1200 kHz, meaning that the top part of the AM broadcast band is cut off. The article notes that this limited tuning range was used “for simplicity and to enable the builder to find the component parts in current radio catalogs.” In particular, instead of having the builder wind the coil, the plans call for a standard oscillator coil intended for a superheterodyne receiver.

The receiver uses a single 117N7 tube, which combines a pentode and rectifier in the same tube. Therefore, both the filaments and the B+ can be obtained from an AC line cord. The chassis is simply a wooden base supported by cabinet knobs. Most of the wiring is under the chassis, although the high voltages are easily accessible to anyone who picks up the radio when it’s plugged in, which probably wouldn’t fly today. The radio puts out enough audio to drive a 5″ speaker, which is simply mounted facing down.

As with many Popular Mechanics electronic projects, the set was also available in kit form from Allied Radio.  It could be found in the 1948 catalog for $10.50.

Most of the parts should be readily obtainable. The most difficult would be the coil, but it is available from Antique Electronic Supply.  It could also be scavenged from an old five-tube AM radio. The tube is available from TubeDepot.com.  For more ideas on where to find parts, you can visit my Crystal Set Parts page or Jameco Electronics.

80 Years ago, the cover of the December, 1934, issue of Short Wave Craft featured this pocket portable one-tube superregenerative receiver covering the 49 meter shortwave broadcast band. According to the article, the receiver was able to pull in Europe without an antenna. And when tested with a short antenna in the magazine’s offices in a steel frame building in New York, the set picked up “stations galore.” The article notes that the receiver’s superregenerative circuit had one serious drawback: It radiates a very strong signal. The article therefore recommended that “it be operated only in the less congested areas where there are few short-wave receivers and where the danger of interfering with others is nil.” In other words, this particular circuit probably wouldn’t pass muster under Part 15 of the current FCC rules as an incidental radiator.

The author of the article is George W. Shuart, W2AMN, later W4AMN. He also wrote several articles for QST in the late 1930’s through the 1960’s.  His last contribution to QST appears to be a “Hints and Kinks” item in August 1978 for a CW filter.  A 1946 QST article includes a biography which notes that Shuart had been licensed since 1928, and had written numerous articles for beginners, a result of which was that many amateurs got their start from his articles. It also revealed that Shuart was employed by Hammarlund as its Advertising and Sales Promotion Manager. He was the author of the 1937 Radio Amateur Course
published by the same magazine in which appeared this one-tube radio.

The 1934 article provides two possible solutions for carrying the batteries for this pocket radio. The filaments run on two penlight cells, and the B battery can be as low as 22-1/2 volts. One solution is to make the B battery out of penlight cells bundled together and carried in a pocket. The other alternative is to mount them on a strap “which forms a belt that can be worn around the waist. This is an old stunt used in stage tricks.” A picture of this arrangement is shown in the article, and I would advise against wearing this type of battery while visiting an airport.

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Seventy-five years ago, Popular Science, December 1939, showed how to make this handy radio to be clamped onto any convenient floor lamp (or simply be used as a standard table radio). It had a myriad of potential uses. “Mounted on a bridge lamp it provides a radio for card games; attached to a floor lamp beside your favorite chair it puts the evening’s programs at your finger tips; and fastened to a standing lamp in your bedroom it serves as a convenient bedside set.”

Frankly, the “floor lamp” feature sounds a bit like an afterthought. The cabinet is hinged and includes cutouts to go around the lamp. A decorative band on the lamp, or a hose clamp, keeps the radio from sliding down.

The guts of the radio itself consist of a two-tube circuit consisting of two loctal tubes. A 7A7 serves as the regenerative detector, with the regeneration control used to control the volume. A 32L7 serves as the audio amplifier and rectifier. It’s an AC/DC set, with a 220 ohm resistor used to drop the line voltage to power the filaments. Because it’s run right off the AC line, there is a capacitor between the external antenna and the set, which the diagram reveals would otherwise be connected directly to one side of the line cord. The article contains a stern warning that this condenser “is extremely important, since it eliminates any possibility of blowing out the tubes or burning the primary of the antenna coil (which could start a fire) should the antenna wire or antenna lead accidentally come in contact with a grounded pipe or radiator” or, worse yet, some hapless person who happens to be touching the radiator.

I wonder how many people built such a radio. By this time, nearly every commercial radio sold was a superheterodyne, rather than the sometimes tempramental regenerative circuit used here. But still, a radio such as this one would be a pretty good performer, and quite suitable as a second radio after the big one in the parlor.

According to the 1942 Allied Radio Catalog (the new loctals were not yet shown in the 1939 catalog), the tubes would cost a total of $1.36. The least expensive table radio in the 1939 Allied catalog (a four-tube superhet) was $6.95.  Since most of the other parts could probably be scavenged from a broken radio, building this little two-tube set could represent a bargain for someone wanting to boast two radios in their home.

QST, October 1944.

At OneTubeRadio.com, we’e always looking for one tube radios, and seventy years ago, QST carried these circuits for a one-tube AM transceiver for VHF. Since the war had Amateur Radio shut down for the duration, this circuit was designed for WERS on 112 MHz.

The design also took wartime parts shortages into account, since the radio has about the bare number of parts possible to make a functioning transceiver. The author notes that almost any receiving tube can be used, and includes two circuit diagrams, one showing a directly cathode, and one with a separate cathode and filament. A prototype of the unit is shown, built in a cigar box. The antenna, a quarter-wave zepp, plugs into the top of the radio.  (These days, a vertical zepp for VHF is better known as the J-pole.)

The circuit is basically a regenerative receiver, with a carbon microphone controlling current to the cathode. While the modulation percentage is low, the author calls it entirely adequate for short-haul work.

The author recommends a 6J5 tube for the circuit with a cathode, or a 1LE3 or 1G4 for the filament-only circuit, but almost any tube will work. The author does not offer any details as to performance (since he probably wasn’t able to test it on the air during the war). But he notes that “for a transceiver which costs only two dollars or less, as this one does, any attainable range should be satisfactory.”

It’s doubtful whether this simple circuit would meet the current FCC spectral purity requirements for use on the ham bands. After all, even while receiving, the regenerative receiver is radiating. However, if some attention is paid, it’s likely that this circuit would be legal on 49.82 – 49.90 MHz, under sections 15.235 and 15.23 of the FCC rules.

Interestingly, this isn’t the first time that the author of this article has been mentioned at this site. The QST article was written by Gurdon Abell, W2IXK. It appears that he later moved to Connecticut and was licensed as K1EHG after the war.  He passed away in 1999 at the age of 82.  He was mentioned here in an earlier post, and it wouldn’t be incorrect to say that he was the discoverer of meteor scatter communications on VHF.

You can find the original article and a few corrections on the ARRL website. To view these QST articles, you need to be logged in to your ARRL account.

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VHF Antenna at FCC Allegan, Michigan, monitoring station, 1944.

Seventy years ago, the November 1944 issue of Radio News carried a story of a phenomenon that was baffling radio engineers, and was under investigation by the FCC monitoring station at Allegan, Michigan. The station was reporting strange bursts from distant FM broadcast stations, then operating in the 42-50 MHz band. The FCC station had receivers tuned to the frequencies of distant stations, constantly making a record of the signal strengths as the distant stations came up out of the noise. The signals were bursts of a very short duration in the station’s signal strength. These bursts were rarely of a duration longer than a single spoken word or one or two notes of music.

The bursts have been observed at distances of up to 1400 miles, but were more common at distances of 300-700 miles.

The article was almost certainly describing meteor scatter.  A letter to the editor of QST, November 1946, from Gurdon R. Abell, Jr., W2IXK, seems to be the first reference by a ham to the same phenomenon. He noted hearing bursts of signals during the Perseids meteor showers on 144 MHz, which coincided with bursts from New York HF stations inside his skip zone. He concludes, “if this observation can be relied upon, it means that 144-Mc. signals can be refracted by the stronger meteor trails,” and he seeks further corroborating evidence.

This letter was probably inspired by a January 1946 QST article by Oswald G. Villard, Jr., W6QYT.  Villard detailed how to listen to meteors by monitoring short wave stations on 11, 15, or 18 MHz. A meteor would result in a signal being reflected, but with a doppler shift causing a change in frenquency. The two signals would result in a heterodyne, causing an audible whistle.  Villard followed up with another article in QST for July 1947,  but was still focused on the HF effects of meteors, the highest frequency investigated being 27 MHz.

Two follow-up letters to W2IXK’s appeared in QST in January 1947, from Villard, and also from Bruce Henke, W6TFJ, who noted a similar phenomenon on 10 meters. In April 1953, Villard, along with Allen Peterson, W6POH, wrote an article discussing the possibility of using “meteor scatter” for communications on 15 and 20 meters.

Between 1953 and 1956, VHF operators started to figure out the possibilities of this propagation mode. Many of these are detailed in the World Above 50 Mc column in October 1956.

With digital modes, able to make an entire exchange in less than a second, meteor scatter is now fairly routine. In the 1950’s, it required fast Morse code, and more than a little luck. It’s not impossible, however, with voice modes. From Minnesota, South Dakota is a difficult catch on 10 meters, since it’s well within the skip zone. I have South Dakota confirmed, and I’m pretty certain it’s courtesy of a meteor. During a 10 meter contest, I just happened to have the VFO on the frequency being run by W0SD in Salem, SD, a distance of 225 miles. (If you’re driving I-90 through South Dakota and wonder what those towers are as you pass Salem, now you know.)  He was calling CQ, and he came up out of the noise with a booming signal. I quickly called, we made the exchange, and then he disappeared. He was audible for only a few seconds, and it was dumb luck that I was on his frequency for those seconds. I can’t think of any explanation other than meteor scatter for this contact.

Note:  To view the QST articles linked above, you need to be logged in to your ARRL account.

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