Variable filter for DX

EE 60 January 1986 by J Barendrecht VARIABLE FILTER FOR DX The filter described in this article will effectively combat the irritating occurrence of a weak, distant radio station being almost completely blotted out by a much stronger one. Moreover, it enables any in-band beat whistles to be silenced Just what many DXers have been waiting for! Fig. 1. By cas- cading tuned filters, a vari- able audio pass-band is obtained. The notch filters help to put a stop to any in- band "whistles! Among the stations transmitting in the short-wave (SW) bands, i.e. about 3 .. .30 MHz, are broadcast, utility and radio amateurs. Many short-wave listeners, often called DXers, delight in the reception of less usual signals in these bands, transmitted by far- away, low power stations presenting very weak signals. To receive those distant stations, DXers often exhibit a remarkable patience and skill to pick the desired signal from a number of strong ones at or near the DX frequency. The SW bands are ve...