VLF converter

I N VLF converter Strictly speaking, the VLF (very low frequency) band stretches from 3 kHz to 30 kHz, and the LF (low frequency) band, often called the long-wave- band, from 30 kHz to 300 kHz. The converter described here covers the frequency range 10...150 kHz and falls, therefore, half-way between being a VLF and an LF converter. Frequencies between 10 kHz and 150 kHz are converted to 4.01...4.15 MHz which can be fed to any short-wave receiver capable of accepting those frequencies. The con- verter is connected to the aerial input of the receiver via coaxial cable. Many converters suffer from break- through of the mixer/oscillator fre- quency in the output signal, which is normally caused by the mixer being asymmetrical. Because of that, the present converter uses the well- known S042P frequency changer, the symmetry of which can be set accurately with a 1 k preset poten- tiometer connected between pins 10 and 12. To prevent reception of image fre- quencies, the aerial signal i...