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Propagation

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No matter what receiver and antenna you have, as a shortwave listener we are all affected by the solar, seasonal and diurnal cycles of our sun. Even at the solar cycle minimum - which we passed in mid- to late 1996 - the few sunspots can kick out energy that affects radio reception. At the mid-2000 peak of cycle 23, we can expect an increasing number of disturbances that are usually more severe on the upside of a solar cycle than when the cycle and sunspots are on the decline.

Mount Wilson (California) Observatory, 1917

When we encounter ionospheric storms and sudden ionospheric disturbances, even those with the best of receivers and antennas will encounter times when shortwave reception is severely degraded. A knowledge of propagation, grayline and trans-equatorial reception can produce some interesting listening even under the worst of conditions.

Propagation data broadcasts

Daily propagation data is broadcast by the USA's standard frequency and time signal stations. On WWV (Colorado: 2.5, 10, 15 and 20 MHz), the broadcast is 18 minutes past the hour; on WWVH (Hawaii: 2.5, 5, 10 and 15 MHz), 45 minutes past the hour. Three numbers are broadcast.

The data includes the solar flux, a measure of activity on the sun. The numbers range from 0 to 400. Practically, the lowest the number at a solar cycle minimum will go in a solar cycle is 66. The A-index and K-index are measures of geomagnetic activity, centered on the poles, on the planet. The A-index numbers also range from 0 to 400; the K-index, 0 to 9. The solar flux and A-index data is updated daily at 21 UT; sometimes the numbers are revised ever-so-slightly at 00 UT. The K-index is updated every three hours starting at 00 UT.

If you follow the K-index throughout the day, you can get an early-warning indication on changing propagation conditions. Additional announcements on propagation conditions, solar flares, geomagnetic storms and the like are also updated every three hours. Here's the relationship between the A- and K-indices:

A 0 3 7 15 27 48 80 140 240 400
K 0 1 2 3 4 5 6 7 8 9

Some observations

The solar flux has a positive effect on the maximum useable frequency. As the number increases, so will your opportunity to hear stations on the higher frequencies. The A- and K-numbers have a negative effect on your opportunity to hear stations from afar.

As these numbers increase, so will the signal absorption increase around the poles. Signals with high-latitude reflection points transversing near the north and south poles will be disappear into the noise. For example, under geomagnetic storm conditions we on the east coast of North America will first lose reception from such stations as Radio Korea and Radio Pyongyang.

Experience has shown us that a geomagnetic disturbance actually enhances signals that cross the equator. The combination of loss of signals from Europe and Asia and the increased ionization over the equator allows us to hear otherwise difficult to hear stations from a southerly direction. During the east coast North American evening hours, we use RAE (Argentina) on 11710 kHz as an indicator. As the A passes 15, 20 and 30, RAE is heard very well. When conditions are normal - at and near the bottom of the solar cycle - RAE is difficult to hear. During a minor-to-moderate disturbance we also enjoy better than normal reception of Radio New Zealand International on 17675 kHz and the Radio Australia frequencies on 17 and 19 meters during our evening hours.

Further reading

Check out your local library, bookstore or radio store for a variety of amateur radio and SWL publications. Two publications in my library are:

Jacobs, George and Cohen, Theodore. The NEW Shortwave Propagation Handbook. CQ Publishing, Hicksville, NY. ISBN 0-943016-11-8, 1995.
Hirman, Joseph W., and Rosenthal, David A. "A Radio Frequency User's Guide to the Space Environment Services Center Geophysical Alert Broadcasts". NOAA Technical Memorandum ERL SEL-80. Revised May 1992. Order from: Space Environment Services Center (SESC), R/E/SE2, 325 Broadway, Boulder, CO 80303, USA. Free upon request.

And David Rosenthal also wrote the Radio Netherland's publication The Solar Guide, available on their Web site.

Simon Collings, G4SGI, discusses propagation in more detail. It is recommended reading. Take a look. Tomas Hood, NW7US, has a comprehensive page of current propagation data and photographs at his site in Washington, USA; Hood replaced Jacobs as CQ's Propagation Editor in January 2002.

For a comprenhensive survey of propagation material, check out Radio Propagation Sources on the Radio Netherlands' site. And in November 1998 we watched a solar flare develop and fade in real time. Check out Blackout! for details how you can do the same.

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19 March 2002