Predicted Radio Receiving Conditions
March 1965 Popular Electronics

March 1965 Popular Electronics   Table of Contents Wax nostalgic about and learn from the history of early electronics. See articles from Popular Electronics, published October 1954 - April 1985. All copyrights are hereby acknowledged.

The sunspot cycle in 1965 was at the same point as it is today - at a minimum (see chart) - so this article is back in style. Sunspots affect high frequency (HF) radio wave propagation in the Earth's ionosphere by generating greater ultraviolet (UV) and x-ray radiation that affects the conductivity of the ionosphere's D, E, and F layers. Although sunspots are cooler areas on the sun's surface, bordering them are plages, which are actually brighter and emit higher levels of charged particles (plasma) that also affect conductivity of the ionosphere's upper layers. Sunspots improve long distance communications on some bands. A sunspot is distinctly different from a coronal mass ejection (CME), which is a chunk of highly charged plasma spewing out from a solar prominence. If released in our direction, a CME can cause profound disturbances in the atmosphere due to electron interaction with the Earth's magnetic field (aurorae are an accompanying effect). Unlike CME's, a sunspot does not need to directly face the Earth to produce an effect; if we can see it, it can affect us. CME's inhibit long distance communications in most bands. Quantitative (measured) ionospheric science was at its infancy in 1965. The International Geophysical Year (1957-1958) had as one of its primary goals to commence a concentrated study of the upper atmosphere and its effects on radio propagation. By no coincidence, Russia's Sputnik and the U.S.'s Explorer satellites were launched then, directly leading to the discovery of the Van Allen radiation belt.

How the short-wave bands will be in March and April plus some information on the poor conditions expected

By Stanley Leinwoll, Radio Propagation Editor

Major international short-wave broadcasting schedule changes will become effective Saturday, March 6, at 2000 EST. Here is a summary of expected conditions in the high-frequency bands for March and April.

11 Meters. Because of the low level of sunspot activity, ll-meter signals cannot be propagated via sky wave during the spring season. None of the short-wave broadcasters have scheduled transmissions in this band.

13 Meters. Activity in this band is ex-pected to be below winter levels. Principal users will be the Voice of America and the BBG between the hours of 1000 and 1800 GMT (0500-1300 EST). Interesting DX possibilities in this band include Ghana on 21,530 kc. between 0900 and 1100 EST, Aus-tralia' on 21,540 kc. from about 2000 EST, and Pakistan on 21,590 kc. between 0500 and 0900 EST.

16 Meters. Fairly good DX'ing should be possible throughout much of the day. Considerable use of this band will be made by the Europeans from early morning to shortly after noon, EST. Ecuador, on 17,890 kc., is about the only Latin-American country scheduled to broadcast in this band, and the best time for reception is around 1500 EST. Congo, on 17,720 kc., during the period from 0800 to 1000 EST, is another attractive possibility.

19 Meters. This band will be most pro-ductive for DX during the daylight hours, from very early morning to evening, with reception from all parts of the world pos-sible at some time during the period when the band is open. During the morning hours until mid-afternoon (EST), for example, reception should be good from Europe, Africa, the Near East, and Latin America. During the late afternoon and evening, re-ception will improve from Asia and Aus-tralia, and continue from Latin America.

25 Meters. Conditions in this band will improve over those observed during the winter, when DX to many parts of the world was relatively poor. In the spring, the ionosphere begins to stabilize-usable night-time frequencies get higher, while optimum daytime frequencies get lower. This sea-sonal trend makes the 25-meter band useful for longer periods of time. In general, re-ception from Europe, the Middle East, and Africa should be possible during middle to late afternoon, local time. During the eve-ning hours, the Latins will be predominant, while best DX possibilities from the Pacific should exist during the morning hours.

31 Meters. The seasonal trend toward higher usable nighttime frequencies will re-sult in improved conditions in this band. Reception from Europe, Asia, and Africa should be possible from mid-afternoon into the evening hours, when South and Central American stations will dominate. During the mid-morning hours, reception of sta-tions to the west will be best. Among the better DX possibilities in this band are Ku-wait on 9520 kc., Guinea on 9650 kc., Senegal on 9720 kc., and Israel on 9725 kc., all during the afternoon hours, EST.

41 and 49 Meters. These bands will open up for DX reception during the late after-noon hours, local time, and will remain open from one area of the world or another throughout the night. Although interference levels will not be quite as bad as they were during the past winter, they will neverthe-less be serious enough to hamper many of the better DX catches. Some stations, how-ever, should be exceptionally strong during the late evening hours. In general, DX re-ception should begin during the afternoon from stations in Europe, the Middle East, Asia, and Africa. The distant Latins will start coming in shortly afterward. For the late night DX'ers, signals from the east will start going out several hours before dawn. Stations from the Pacific should be heard at this time, and should continue to be heard until several hours after sunrise.

60 and 90 Meters. Conditions will deteri-orate in the spring. During the past winter, the combination of low sunspot activity and a record number of users made DX reception in these bands the best in history. With the approach of summer, static levels will increase and signals will grow weaker. However, there will still be a few good DX openings during the hours of darkness.

Standard Broadcast Band. The record-breaking DX conditions observed during the winter months have come to an end. Sig-nals in the standard broadcast band are growing weaker, and noise levels are in-creasing. This trend should continue as the season progresses, nights grow shorter, and maximum usable frequencies increase. Good DX will still be possible, but for shorter periods of time, and not nearly to the extent observed in December and January.

Long-Wave Band. Some interest has been expressed in reception of signals in the long-wave band, between 150 and 285 kc. The Geneva Radio Regulations of 1959 allocate this band to AM broadcasting in Europe, Africa, and part of Asia. Long-wave broad-casting is fairly popular in Europe, although not as popular as medium-wave (or what we call "standard") broadcasts.

In general, long-wave propagation is similar to medium-wave propagation: conditions at night are much better than during the day, and propagation in winter months is better than in the summer. One problem with reception of long-wave broadcasts that is more serious than in any other part of the spectrum is the type of antenna required. Wavelengths in the kilocycle range are extremely long, being on the order of about one mile at 180 kc. This means that a simple half-wave dipole antenna would have to be half a mile long at this frequency to be effective. Listeners cannot be expected to erect such antennas, so a fairly long wire must do, which means a loss of signal strength. This fact - coupled with the fact that as we go down in frequency, static levels and absorption in the ionosphere increase - results in reception that is generally inferior to that in the medium-wave broad-cast band.

Ionospheric Storms. From time to time disturbances occur in the upper atmosphere which tend to disrupt long-distance communications by severely upsetting the stability of the ionosphere. Such disturbances are most likely to occur during the spring and fall equinox - March and April, and September and October - when the earth passes through the plane of the sun's equator. They fall into two general categories: the ionospheric storm and the sudden ionospheric disturbance (SID). Ionospheric storms usually develop gradually and continue from several days to almost a week. The SID, on the other hand, commences suddenly, and seldom lasts more than an hour.

Although they are different in nature, both disturbances have the same effect on communications: during storms, signal levels fall off sharply, fading becomes se-vere, and the general quality of DX reception deteriorates. During extreme conditions, a radio blackout may occur during which it becomes impossible to maintain high-frequency communication with many areas of the world.

During the early days of radio (the 1920's), it was not unusual for SWL's and amateurs to rip their receivers apart during radio blackouts because they thought something had gone wrong with the sets. Nowadays, we know better. Ionospheric storms are caused by bursts of radiation from the sun. This radiation, composed of either extremely intense ultraviolet radiation, or subatomic particles from an explosion on the sun, or both, saturated the ionosphere, resulting in a tremendous increase in radio-wave absorption, which in turn results in a sharp decrease in signal levels.

Posted March 7, 2018