Fifty years ago this month, the cover of the March 1965 issue of Electronics Illustrated showed this integrated circuit, the Motorola MC556G. The case of this IC measured 5/16 inch in diameter, and the chip itself measured about 1/10 inch square. It contained six transistors and eight resistors. The accompanying article noted that it was now on the market at a price that hobbyists could afford to use for experimental projects,  $3.35.

To put the new device in perspective, the article compared it to the still ubiquitous 5-tube radio, which consisted of about six basic circuits using about 20-30 components. The article noted that the day would soon arrive when one or two IC’s would constitute a “complete radio that is equivalent in performance to that five-tube AC/DC job.”  That prediction came true only seven years later, in 1972 with the ZN414 AM radio IC from GEC-Plessey. The modern functional equivalent of that IC is the MK484/TA7642 am-Radio IC, which is a complete radio in a chip, requiring as its only external components a battery, coil, tuning capacitor, and earphone.

While the eight transistors in a 1/10 inch package was revolutionary at the time, transistors in current IC’s are in the range of tens of nanometers in size, allowing several billion transistors per chip. But building something with an IC was revolutionary fifty years ago, and Electronics Illustrated featured two projects making use of the MC356G. The first was a square-wave signal generator, and the second was the AM radio shown below. In this diagram, the portion shown in black is internal to the IC, and the components shown in red are external. As you can see, the circuit makes use of four of the chip’s eight transistors, and four of its resistors.

The IC was designed for use as a logic gate, but transistors are transistors, and they could be used for their amplification function. For the radio in particular, getting the circuit to work took several experimental designs, but the author finally “hit upon one that has a decent amount of sensitivity, selectivity, and audio output.” The author noted that most of the headaches in designing the radio were caused by the close proximity of the components on the chip. Having only 1/10 of an inch to work with presented leakage paths between the circuits that would be out of the ordinary for a radio designer.  The finished project is shown here.

In the design, two of the transistors are used as RF amplifiers, with the signal being fed back through a regeneration control. The second of those transistors also amplifies the audio, and there are two more audio amplifier stages. The actual detector consists of two external diodes.

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An interesting ionospheric effect was first noticed about 80 years ago, and reported 80 years ago this month in Radio Craft magazine, February 1935.  Radio Luxembourg operated on 252 kHz, with a powerful 150 kw signal designed to provide coverage in England.

The phenomenon was discovered in 1933 by B.D.H. Tellegen, in Eindhoven, Netherlands, who was listening to a station in Beromunster, Switzerland, on 652 kHz. In the background of the Swiss signal, he could hear the audio of Radio Luxembourg. This same phenomenon was reported by other listeners. Due to the distance between the three points involved, it could not be explained by the receiver being overloaded. The Luxembourg signal could be heard only when the Swiss station was transmitting.

Tellegen noted that the three points were in a straight line: When the signal from the Swiss station made its way to the Netherlands, it passed directly over Luxembourg. He correctly theorized that the carrier of the Swiss station’s signal was being modulated in the ionosphere as it passed through the strong signal of Radio Luxembourg in the ionosphere.

The ionosphere had only recently been discovered, and was not totally understood. It was previously supposed that the ionosphere was a linear medium, through which radio waves passively reflected. But the existence of the Luxembourg Effect showed that the ionosphere could be artificially “heated,” to produce non-linear effects.

Interestingly, the carrier frequency of the signal didn’t seem to be critical.  The modulation of the interfering signal was superimposed on the other signal without regard to the carrier frequency.  Subsequent research showed that most of the effect took place in the lower range of the audio frequencies.

Much to the dismay of conspiracy theorists, this is the phenomenon that the High Frequency Active Auroral Research Program (HAARP) was working with. It’s relatively easy to generate a strong radio signal in the High Frequency (HF) region. HAARP had transmitters that could generate 3.6 MW signals from 2.8-10 MHz and radiate them toward the ionosphere. This strong signal was able to generate the same kind of “heating” effects caused by Radio Luxembourg.

It’s more difficult to generate signals in the Extremely Low Frequency (ELF) region. Among other things, ELF signals are used to communicate with submarines. The main idea of HAARP was to generate these signals not in a transmitter, but in the ionosphere itself, by mixing two strong HF signals. For example, it would be practically impossible to generate a radio wave of 0.1 Hz with a transmitter. But by beaming two signals into the ionosphere, one at 4.000000 MHz, and one at 4.0000001 MHz, the result would be a radio wave, generated in the ionosphere, with a frequency of the difference, 0.0000001 MHz, or 0.1 Hz.

The phenomenon is sometimes called the Luxembourg-Gorky effect, since the powerful longwave transmitter at Gorky, USSR, produced similar effects.

References

• Probing the Northern Lights, Popular Mechanics, July 1999.
• PHD Dissertation by Juan Valentin Rodriguez, 1994, at page 5.
• Radio Science for the Radio Amateur by Eric Nichols, page 11-7

Radio parts were in short supply during the War, and radio enthusiasts had to make do with what they had. “H.T.,” a resident of Bothell, Washington, apparently had in his junk box a 1D8GT tube, and a low-impedance earphone, and wanted to know what he could do with them. So he wrote to the editors of Radio Craft magazine asking for a diagram of a receiver covering the broadcast band making use of the parts he had. He wanted to mount the earphone in the cabinet for use as a small speaker.

The editors indulged him and provided this diagram in the February 1945 issue. It was reprinted from the July 1940 issue, and showed how the combination diode-triode-pentode tube could be used in this circuit. The triode section of the tube was an RF amplifier, followed by the diode detector, with the pentode serving as an audio amplifier. Unfortunately for H.T., the low impedance earphone would need to be used in conjunction with an audio transformer. This set would drive a pair of high-impedance headphones, but to use it with his low-impedance earphone, it would need to be wired as shown for the speaker. So H.T. had to find himself either a set of hi-z headphones, or the output transformer, in addition to what he already owned.

The other hard-to-obtain part would be the variable capacitor. The circuit here shows a ganged condenser, but the response pointed out that two separate condensers would provide better results.

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