IMPROVING THE QUALITY OF SHORTWAVE BROADCAST RECEPTION INDOORS BY USING AN ANTI-FADING PROBE ANTENNA

When shortwave (SW) broadcasts are received on self-contained receiver s indoors, there generally is a reduction in signal strength and an in crease in the speed and depth of fading in comparison with reception i n open spaces outdoors. Even when the received signal level is adequat e, the quality of reception indoors is degraded. This comes about beca use the fields indoors ate a superposition of components of radiated s ignal from the distant transmitter plus other components representing energy reradiated or scattered by nearby conductors such as house wiri ng or plumbing. Since many of the near-field components originate very close to the receiver, it is possible to reduce their effect by deriv ing the receiver input from two or more probes-i.e., pickup devices sp ecially designed to respond to fields in their immediate vicinity with out disturbing those fields. To achieve the desired probe action, adva ntage can be taken of the high input impedance of portable, battery-po wered receivers designed for use with small telescoping whip antennas. Spacing of multiple probes in the order of a few tens of centimeters suffices to give an output significantly smoother and of higher qualit y than that obtainable with the receiver's whip antenna by itself. The high signal levels of many SW broadcasts make it practical to use sma ll, inefficient antennas. This article describes an Anti-Fading Probe Antenna (APA), which produces a worthwhile improvement in reception qu ality indoors. It is simple to build, requires no adjustment, and may even improve received signal quality in some outdoor situations.