• Propagation
• Natural background noise
• Man-made interference

Propagation

Though propagation is a fascinating topic unto itself, the purpose of this document is not to delve into the mysteries of the sun and its effects on the ionosphere. For more information, Appendix 1 includes a selected list of publications dealing with propagation and antenna topics. Also see our own Radio Propagation Sources.
No matter what receiver and antenna you have, as a shortwave listener we all are all affected by the solar, seasonal and diurnal cycles of our sun. As we approach the solar cycle 22 minimum early in 1996 and encounter ionospheric storms and sudden ionospheric disturbances, even those with the best of receiver 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. Daily propagation data is broadcast by the USA's standard frequency and time signal stations WWV and WWVH. The data is available for those with computers via the Internet in rec.radio.info and rec.radio.shortwave newsgroups.

Further, your geographic location and proximity to the transmitter site can have an effect on reception conditions. The intensity of solar radiation varies with latitude. The greater radiation at the equatorial zones than the polar ones increases the maximum and minimum useable frequencies. Conversely, the effects on reception of the tilting ionospheric layers at the twilight period are longer at the higher latitudes, where the rate of change is slower than at the equator where the width of the twilight zone are narrow. A computer program such as the PC-compatible shareware-program GeoClock clearly show the varying width of the twilight zone.

The transmitting frequency, the skywave angle, the length of the skip zone and the groundwave can also affect reception conditions. If you are in the no-man's land beyond the range of the groundwave signal range and less than one skywave hop's distance from the sender site, reception will be virtually non-existent.

There is little that you can do when propagation conditions adversely affect reception. The right antenna choice may maximize reception, and selecting a different frequency from a different relay site -- for example, Radio Netherlands uses senders at Bonaire, Madagascar, and several CIS sites -- may help.

Natural background noise

An antenna not only picks up radio transmitters but also background noise. There are in fact various types. Galactic noise is one example, the sun being the main source. Up to about 100 MHz, inter -stellar noise is also present. Alongside that we have atmospheric noise. This is partly caused by the approximately 30,000 thunderstorms that occur each day across the globe. All the lightning produced adds to the background noise, though the level does depend on where you live. Listeners in the tropical zones of the world suffer much more from this type of interference.

Man-made interference

This noise is caused by the millions of electrical devices in use at the moment, from washing machines to fluorescent lamps, and from drills to car ignitions. Even if you live out in the country, overhead high-tension power lines can act as giant antennas 'broadcasting' electrical noise right across the spectrum. All this electrical interference forms a background of man-made noise which, even in the countryside, is some 10 times stronger than atmospheric noise. Beware of this interference field ! It surrounds every house! It is caused by electrical equipment inside the dwelling, especially devices such as dimmers, TVs, computers, video-recorders, and thermostats. Even if you don't use such apparatus when listening, there is a good chance that the neighbors do.

The mains electricity cables also bring many sources of interference into your house, and this in turn is radiated by all the electricity cables. This interference field stretches some 5 meters around the house, and about 1 meter above it. So it is always a good idea to hang the antenna away from this interference field.

If you have a portable radio that can be tuned above the medium wave band and can unplug appliances or turn off circuit breakers, you may be able to isolate the offending apparatus. Contact the manufacturer and ask for a noise suppression kit. Perhaps your neighbors may cooperate in your hunt for the noise. If the noise can be traced to the outside, ask your electric company for assistance in identifying and eliminating the noise. It is not uncommon to find broken ground connections, failed or broken connections on the pole, broken insulators or failed transformers or lights.
Letters from listeners to Radio Netherlands indicate that help from local authorities varies. The majority do not seem to be sympathetic.

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