Strangely Behaving Signals

While the causes for QRM were well understood, mostly man-made, and could be dealt with through cooperation and tuning techniques, other disruptive on-air phenomena were clearly beyond such controls: those caused by nature. Some, such as static (QRN, also called strays), although understood to a large degree, had no known effective remedy.  Others, such as fading, were not understood at all. At constant transmitter power, what natural phenomena could possibly cause a signal to fluctuate in strength? Why wasn’t a transmitter’s signal strength simply determined by the distance to the receiver?

One west coast amateur who wrote to QST about signal fading, wondered if east coast amateurs were experiencing anything similar.1 He cited an IRE2 Proceedings article (vol. 4 no. 2) that discussed the phenomenon, and a “Captain Bullard” who had offered a theory of a conductive layer above the earth at an altitude that was higher in the daytime and lower at night. This might account for the stronger nighttime signals because the energy in the waves was being confined to a smaller space. He was almost right.

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Prof. A. Hoyt Taylor held a Ph.D. in physics and had most recently taught at the Universities of Wisconsin and North Dakota.3 Also an active ham operating under a special license as 9XN, he had taken an early professional interest in radio propagation and antennas. In QST he discussed sources of signal variations (without ever using the word propagation)4 based on experimental results he had already published in the IRE Proceedings.5

Differences in signal behavior between day and night, summer and winter, were well known but their origins were not. By “variations,” Taylor meant real-time changes in strength (often referred to as freaks or swings, and now called QSB), which were most often noticed at twilight. They were also more noticeable at long distances and short wavelengths. He therefore suggested experimenting during winter nights when long distances became more possible with short wavelengths.

Taylor further observed that signals fell off with distance much faster than the inverse square law6, which applied in free space, would predict. The extra decrease was thought to be due to absorption by the air and ground, and Earth-bound objects such as vegetation and buildings. Moreover, short waves at night exhibited very confusing behavior. They could be louder than would be expected with no absorption at all, then could rapidly fade to almost nothing. He concluded that this could only happen if direct waves were interfering with waves reflected by some upper layer of the atmosphere. The two path lengths would be different and thus signals following different paths could combine at the reception point to enhance or degrade each other.

During the winter of 1914-1915, he performed all-night experiments using 1500- and 500-meter waves, expecting to find that variations observed at 1500 would all be present at 500 too, but not the converse, given the 3-to-1 wavelength ratio. His results seemed to support that theory.

He suggested additional experiments and noted something we take for granted today, that “Cases where the waves seem to skip an intervening station are of especial interest and should be carefully noted. A number of well proven cases are on record where signals have been more audible at say 700 miles than at 350 miles, the sender and two receivers being all in a line. It is difficult to explain such cases except by the action of interfering reflections.” Taylor concluded that “freak records” for distance covered were probably not a valid way to rate the effectiveness of a station since these occurrences were haphazard exceptions rather than demonstrations of consistent or inherent capability.

Other theories explained bending of waves along favorable paths,7 speculating about the effects of sunlight and that decreased ionization of the air at night was probably responsible for the improved propagation. They were right but for the wrong reason. The shorter the wavelength the greater the observed enhancement was at night. This was a hint of great things to come.

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Calls Heard banner-June-1922 PS

Terman letter - calls heard March17 QST p39 v2-For some time, QST had been printing lists of stations heard, as reported by members around the country. Located towards the back of the magazine, at first mixed in with the letters to the editor, it was known as the Calls Heard section. Polling indicated there was very strong support for continuing the practice, many finding it quite useful in judging the effectiveness of their stations along various paths from month to month.

This was a time when establishing two-way contact was itself quite challenging. Thus, just hearing another amateur’s signals was useful information to convey by other means (i.e. via QST) back to the transmitting station’s owner.

The editor noticed “many queer things” that could be inferred from these lists with regard to fading. The most prominent question was, why were stations further distant heard more reliably than ones closer in? And why could a station at the foot of a high mountain hear stations 800 miles beyond it? This made no sense at all for waves propagating along the ground. Noticing the effects of ionospheric propagation, amateurs did not yet understand it.

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A very early Calls Heard section included a letter from 16-year-old Fred Terman (misspelled “Texman” in QST). Terman would later become professor of electrical engineering at Stanford University, author of seminal text books on radio engineering, and one of the founders of Silicon Valley.

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In the midst of ever expanding range, a QST editor, probably Maxim, asked “Where Are We Bound?”—that is, where is message relaying taking us?8 Licensed amateurs were then 5,000 strong in the US. They held regular traffic handling schedules. Some stations had as much as $1,000 invested in their stations (equivalent to nearly $18,000 in 2013). A thousand miles was now being covered with a kilowatt or less, using 200 to 300 meter wavelength, something newly possible for “twenty or thirty of us” every night. He also wondered how the presence of inexpensive or free communications (neglecting the cost of equipment) between citizens would affect the telephone business. And what new and ever better equipment and technology would result from the demand for amateur wireless apparatus? Would other countries stop suppressing amateur operation, as they were now doing? Finally he noted,

And last of all, we wonder if you and I some night in the future will sit in our little room and chat with another fellow in Germany or France while we listen to what is going on between a couple of fellows, one in Brazil, and the other in Honolulu? We realize this last is a pretty good ‘wonder’ but if we advance as much in the next ten years as we have in the past ten, it will be something to confidently expect.

And 9DC offered his own poetic take on propagation and the pleasure in operating:

… As I sit here upon my hard-bottom chair, with receptors screwed to my auditory organs, I seem to be possessed of a superhuman position. In fact, it is like flirting with spirits, chasing unimaginable demons of the firmament, and kidding the devil. Indeed, I listen to the mouth of the world give forth its grievances of a day, with ears like those of a God. As the hours grow smaller, the green shaded filament before my orbs appears to grow more subdued, but more effective with its tormenting rays. I am surrounded by the playthings of spirits. They generate a flaming liquid. It is hot. It cracks as it flows. It renders the air asunder as it passes over a non-metallic circuit (spark gap). It jumps forth from its origin upon every air line of the earth. It dies no sooner than born, but how far it has traveled in its short career, no one knows. Indeed, the most delightful and fascinating thought comes from the anticipation of reaching some distant hamlet or city… -9DC.9

Nearly a century later, this anticipation remains a source of delight and fascination for many hams.

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  1. L. Winser, “Radio Communications by the Amateurs,” QST, June 1916, 141.
  2. The Institute of Radio Engineers, one of the pieces that combined later to form the Institute of Electrical and Electronics Engineers (IEEE).
  3. He was chairman of the physics department.
  4. A. H. Taylor, “Transmission Variations,” QST, August 1916, 189.
  5. Taylor would go on to be superintendent of the radio division at the Naval Research Laboratory from 1923 to 1945 and contribute to the development of RADAR. He was also President of the Institute of Radio Engineers (IRE) in 1929.
  6. The strength decreases with the square of the distance, e.g. double the distance and the signal decreases to one-fourth.
  7. The Propagation of Wireless Waves,” QST opening article, September 1916, 235
  8. Where are we Bound?,” Editorial, QST, February 1917, 36.
  9. 9DC, “Q.R.M.,” Radio Communication by the Amateurs, QST, March 1917, 45.

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