Monthly Archives: May 2017

1977 Indoor CB Antenna

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For the woman shown in this picture, from an ad in the May-June 1977 issue of Elementary Electronics, the CB was probably her connection with the outside world, and her social life probably revolved around the good buddies she met on the air.  She was probably a REACT member, and used her CB to help motorists in need.

But she had a big problem when she moved into a new apartment where outside antennas were not allowed.  Fortunately, Hustler came to the rescue with this indoor CB antenna, dubbed the “Homing Pigeon.” According to the ad, this antenna was the answer to operating the CB from any location, such as a condominium, office, home, apartment, or motel. The spring-loaded antenna required no installation, and was supported by the floor and ceiling “like a pole lamp.” According to the ad, the range was “equal or superior to better mobile installations.”

Of course, the construction of the building probably played the biggest factor. Such an antenna would probably work well from a wood-frame house. From a building made of steel, it probably wouldn’t work quite so well. In this installation, placing the antenna next to the ductwork probably didn’t help.  But this was probably outweighed by getting it next to the exterior wall, and she probably got out pretty well in that direction.

When I worked for Radio Shack in an earlier lifetime, we sold a similar antenna, a half-wave coaxial antenna which sold for $34.95.  It was billed as “New for ’79” in the 1979 Radio Shack catalog.



History of the Coherer

1967MayPE1

Fifty years ago this month, the May 1967 issue of Popular Electronics took a look at the earliest days of radio. In particular, it looked at the coherer, and even showed plans for making the one shown above.

The coherer was one of the first methods of detecting radio waves. In 1850, the French scientist Pierre Guitard had discovered that dust particles in the air cohered, or collected together, when electrified. This principle was later used as a radio detector. Iron filings were placed in a glass tube, and in the presence of a radio wave, they cohered. The presence of the radio wave could be observed directly by looking at the filings. Or, more importantly, the iron filings would provide a current path to operate a bell or other device.

As far as I can tell, the coherer has absolutely no practical value today.  Even the most rudimentary crystal detector outperforms it, and has the added advantage of being much simpler to make.  But for those interested in experimenting with one of the artifacts of the earliest days of radio, the Popular Electronics article gives enough information to make a working example of the earliest radio detector.

1967MayPE3Electromagnetic fields were first predicted in 1864 by James Clerk Maxwell. It wasn’t until 1887 that this was proven experimentally by Heinrich Hertz, who transmitted a 75 MHz radio signal about 50 feet with the setup shown here. The transmitter consisted of a spark gap not unlike the transmitters used commercially in the early days of radio. The receiver consisted of a loop of wire with an open gap. The radio signal could be observed in the form of a spark in that gap. Hertz discovered that the range could be maximized by adjusting the size of the loop to the wavelength of the transmitted signal.

The next development was the the construction of the first coherer by French physicist Dr. Edouard Branley, which was used by British physicist Sir Oliver Lodge to detect and record Morse code signals sent by a spark transmitter.

After each electromagentic pulse, the coherer had to be decohered manually, since the iron particles remained in place even after the radio signal was gone. Lodge used a “trembler” to decohere the iron filings used in his coherer.

1989 Soviet stamp showing Povov demonstrating first radio, 1895, Wikipedia image.

1989 Soviet stamp showing Povov demonstrating first radio, 1895, Wikipedia image.

The coherer was improved considerably by the Russian physicist Aleksandr Stepanovitch Popov. He used the armature of an electric bell to decohere the particles. With this advance, it was possible to receive code at a reasonable speed. When a pulse was received, the particles cohered, which caused the electric bell to sound, which also decohered the particles. If a signal was still present, the process was repeathed. Popov also had the foresight to attach an antenna to the receiver.  With the antenna, Popov was able to achieve a range of 900 feet.

Basic circuit used by Lodge and Marconi.

Basic circuit used by Popov and Marconi.

Guglielmo Marconi improved the coherer in a number of ways. First, he evacuated the air and replaced the corks at the end with silver plugs. He also replaced the iron filings that had been used previously with a mixture of nickel and silver. Almost immediately, he had increased the range and was receiving signals from 2-9 miles. By 1901, he had increased the range to 200 miles. And on December 12, 1901, he used a coherer to receive signals over 2000 miles from England to Newfoundland.



Andreas Bertnes, LA6R, c. 1916-1941

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This month 75 years ago, the April 1942 issue of QST carried this “stray” item announcing the death of Andreas Bertnes, LA6R, an amateur radio operator from Sendefyord, Norway, who was executed by the Nazis.

Bertnes, a medical student, was a member of a resistance group known as the Ask-gruppen.  The members were rounded up in March 1941.  Three, Bertnes along with Øyvind Ask and Johan Midttun, were sentenced to death on November 22.  They were executed by being shot on December 4 at Trandum.

Bertnes was one of four amateur radio operators executed during the war for their resistance activities.

Bernes was active on the air before the war.  He was listed in the “calls heard” listings by an English SWL on 20 meters in November 1937 and and April 1938.

Reference (and photo)



Jim Crow, 1937

1937May24Life

Eighty years ago today, Life Magazine,  May 24, 1937, carried these images of two separate but “equal” rail cars in the southern United States.  The car on the left was reserved for white passengers, with the one on the right for African Americans.  The caption noted that the car for whites was spotlessly clean and air conditioned, with individual seats.  For the same fare, black passengers travelled in a dirtier car without air conditioning with standard seats.

The magazine feature was prompted by a lawsuit by Rep. Arthur Mitlchel of Illinois, who was then the only black Member of Congress. In April, he had traveled by rail from Chicago to Hot Springs, Arkansas. He traveled in a Pullman car and first class coach until the train reached the Arkansas state line. At that time , as required by Arkansas law, the conductor asked him to move to the Jim Crow coach, which the Congressman called filthy.

He brought suit against the railroad, but made clear that he was not crusading for the end of Jim Crowism. Instead, he was seeking merely the “equal accommodations” promised by the law. He lost before the ICC and the District Court, but ultimately appealed to the U.S. Supreme Court.

The case, Mitchell v. United States, 313 U.S. 80 (1941) was decided in Mitchell’s favor on April 28, 1941.  In 1896, the Court had ruled in Plessy v. Ferguson, 163 U.S. 537 (1896), that “separate but equal” satisfied the Equal Protection clause.  That case wasn’t overruled until 1954 in Brown v. Board of Education, 347 U.S. 483 (1954).  But in Mitchell, the Court held that equal does, indeed, mean equal.

The railroad and the ICC had argued that there was little demand for first class accommodations by African-American passengers.   In fact, the evidence suggested that Mitchell was the first black person to request first class accommodations on the train. But the court held that this was irrelevant, since the ruling “made the constitutional right depend upon the number of persons who may be discriminated against, whereas the essence of that right is that it is a personal one.”

The practical difficulties were irrelevant, according to the court. It was enough that the discrimination had taken place.

 

 



1942 “Command Performance, USA”

1942May24ChiTribSeventy-five years ago today, the May 24, 1942, issue of the Chicago Tribune carried this feature about the shortwave program Command Performance, U.S.A., which began each week with the words, “Command Performance, U.S.A. The greatest entertainment in America as requested by you the fighting forces of America throughout the world, this week and every week until it’s over, over there.”

The article noted that even though the program was intended for servicemen overseas, many Americans with shortwave receivers on the homefront had discovered it and were regularly tuning in.

The programs were transcribed in New York and Hollywood, and featured the biggest stars of the entertainment world offering their talents without charge. The article noted that “sometimes the language on these shows is just a little more robust than is passed by standard broadcasting stations. Jack Benny, as we recall, last Sunday night encouraged our fighting men to ‘give ’em hell.'”

The newspaper carried the schedule shown below of the stations covering the show, along with times and frequencies. It noted that some of the beams were not heard well in the Midwest, but pointed out that many were. For example, it noted that the 10:30 PM broadcast to Central and South America was being heard well in Chicago.

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In addition to Command Performance, special news and sports programs were broadcast for the military, and some domestic programs were rebroadcast.



1957 Hi-Fi Phono Oscillator

1957RadioTVExpCover

Maybe your MP3 player sounds a bit better than this gentleman’s hi-fi turntable from 60 years ago, but I bet you can’t build yours from scratch, like this guy did.  This one, shown on the cover of the 1957 edition of Radio-TV Experimenter, is entirely homemade, and despite the homemade appearance, probably did sound as good or better than anything on the market at the time, and would probably have sounded good even by today’s standards.

It was actually a phono oscillator, and transmitted the signal through an FM transmitter.  Since the audio quality of the FM signal was better than the recording technology of the day, the fidelity was limited only by the quality of the record.

Sound quality was paramount in every detail.  As is plainly visible, the tone arm is indeed made out of wood.  In particular, the wood is basswood, chosen because it had less mechanical resonance than other woods.  Metal would have been inferior, because of the capacitive effect with the leads running through it.

The pickup was homemade, not as a cost-saving measure, but because the design shown here was superior to the ceramic cartridges then commercially available.  It used a capacitive pickup.  The only commercial component was the sapphire-tiped needle, which was pushed into a rubber plug.  A copper plate was carefully positioned next to the needle to complete the capacitive pickup.

The tone arm was cut with a jigsaw, and the article contained precise instructions for balancing it.

The electronics, probably the easiest part to construct, consisted of a small FM transmitter employing a single 6C4 tube.  The example shown here was to be used for 45 RPM records, but the article noted that by adjusting the size and using an appropriate needle, it could be built for 33 or 78 RPM records.



Politically Incorrect Marketing of Radio Parts, 1947

1947MayRadioServDealerSeventy years ago this month, Olson Radio Warehouse had a promotional idea that would probably be regarded as somewhat on the politically incorrect side today. To encourage radio servicemen to order parts and supplies, they instituted the Gift of the Month Club. When the serviceman placed an order, Olson would toss in a free gift. And they kicked the program off by giving away free cigarettes! That’s right: When the serviceman ordered tubes or resistors, Olson would throw in a pack of Camels, Chesterfields, or Luckies!

This piece of trade news appeared in the May 1947 issue of Radio Service Dealer. It reveals that, as of press time, Olson had handed out a quarter million free smokes.



1942 Handheld Radiotelephone

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1942MayRadioCraft2Seventy-five years ago this month, the May 1942 issue of Radio Craft featured on its cover this handheld radio telephone weighing only four pounds, which the magazine noted was not much larger than the handset of a “French” telephone. The set was the product of the Weltronic Corporation, which was the assignee of the patent, U.S. Patent 2276933, with a pre-Pearl Harbor application date of October 1, 1941, and an issue date of March 17, 1942.

1942MayRadioCraftDiagramThe magazine noted that the set had a range of about a mile, and could operate on any frequency between 112-300 MHz. The diagram below reveals that the set appears to be one tube functioning as an oscillator and superregenerative detector, with the other tube serving as AF amplifier to drive the headphone on receiver, and as modulator on transmit.

Commercially available batteries were said to allow continuous operation for eight hours, or about a week to a month in normal service. The article noted that the set was being made available to governmental agencies.

The cover photo shows the unit in use by a guard around a defense plant.

The article puts quotation marks around the word “transceiver,” since such a combined unit would have been unfamiliar to many readers.

1942MayRadioCraftSchematic

 



Congress Institutes Draft: 1917

On this day one hundred years ago, May 18, 1917, Congress passed the Selective Service Act of 1917, authorizing the military draft, now that the nation was at war.

Unlike the draft for the Civil War, the act specifically prohibited the hiring of substitutes:

No person liable to military service shall hereafter be permitted or allowed to furnish a substitute for such service; nor shall any substitute be received, enlisted, or enrolled in the military service of the United States; and no such person shall be permitted to escape such service or to be discharged therefrom prior to the expiration of his term of service by the payment of money or any other valuable thing whatsoever as consideration his release from military service or liability there to.

The first registration under the act, for men age 21-31, was set for June 5, 1917.  18 year olds were set to be registered in 1918.

In 1918, the U.S. Supreme Court held the Act constitutional.