  Propagation, natural background noise, and man-made noise influencereception conditions. Appropriate antennas and receivers can reducebut not eliminate the effects of these factors. Let us examinethese separately. PropagationAs a listener to Radio Netherlands' Media Network, youhear the weekly IPS Radio and Space Services propagation reportsof Mike Bird, Australia, and the occasional propagation featuresfrom David Rosenthal, USA, Media Network Science correspondent.As a user of the annual World Radio TV Handbook you readthe articles by George Jacobs, USA, and Mike Bird. Though propagation is a fascinating topic unto itself, thepurpose of this document is not to delve into the mysteries ofthe sun and its effects on the ionosphere. For more information,Appendix 1 includes a selected list of publications dealing withpropagation and antenna topics. No matter what receiver and antenna you have, as a shortwave listenerwe all are all affected by the solar, seasonal and diurnal cyclesof our sun. As we approach the solar cycle 22 minimum early in1996 and encounter ionospheric storms and sudden ionospheric disturbances,even those with the best of receiver and antennas will encountertimes when shortwave reception is severely degraded. A knowledgeof propagation, grayline and trans-equatorial reception can producesome interesting listening even under the worst of conditions.Daily propagation data is broadcast by the USA's standard frequencyand time signal stations WWV and WWVH. The data is available forthose with computers via the Internet in rec.radio.infoand rec.radio.shortwave newsgroups. Further, your geographic location and proximity to the transmittersite can have an effect on reception conditions. The intensityof solar radiation varies with latitude. The greater radiationat the equatorial zones than the polar ones increases the maximumand minimum useable frequencies. Conversely, the effects on receptionof the tilting ionospheric layers at the twilight period are longerat the higher latitudes, where the rate of change is slower thanat the equator where the width of the twilight zone are narrow.A computer program such as the PC-compatible shareware-programGeoclock clearly show the varying width of the twilightzone. The transmitting frequency, the skywave angle, the length of theskip zone and the groundwave can also affect reception conditions.If you are in the no-man's land beyond the range of the groundwavesignal range and less than one skywave hop's distance from thesender site, reception will be virtually non-existent. There is little that you can do when propagation conditions adverselyaffect 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 noiseAn antenna not only picks up radio transmitters but also backgroundnoise. There are in fact various types. Galactic noise is oneexample, the sun being the main source. Up to about 100 MHz, inter-stellarnoise is also present. Alongside that we have atmospheric noise.This is partly caused by the approximately 30,000 thunderstormsthat occur each day across the globe. All the lightning producedadds to the background noise, though the level does depend onwhere you live. Listeners in the tropical zones of the world suffermuch more from this type of interference. Man-made interferenceThis noise is caused by the millions of electrical devices inuse at the moment, from washing machines to fluorescent lamps,and from drills to car ignitions. Even if you live out in thecountry, 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-madenoise which, even in the countryside, is some 10 times strongerthan atmospheric noise. Beware of this interference field! Itsurrounds every house! It is caused by electrical equipment insidethe dwelling, especially devices such as dimmers, TVs, computers,video-recorders, and thermostats. Even if you don't use such apparatuswhen listening, there is a good chance that the neighbors do. The mains electricity cables also bring many sources of interferenceinto your house, and this in turn is radiated by all the electricitycables. This interference field stretches some 5 meters aroundthe house, and about 1 meter above it. So it is always a goodidea to hang the antenna away from this interference field. If you have a portable radio that can be tuned above the mediumwave band and can unplug appliances or turn off circuit breakers,you may be able to isolate the offending apparatus. Contact themanufacturer and ask for a noise suppression kit. Perhaps yourneighbors may cooperate in your hunt for the noise. If the noisecan be traced to the outside, ask your electric company for assistancein identifying and eliminating the noise. It is not uncommon tofind broken ground connections, failed or broken connections onthe pole, broken insulators or failed transformers or lights.Letters from listeners to Radio Netherlands indicate that helpfrom local authorities varies. The majority do not seem to besympathetic. Comments? letters@rnw.nl |