This device is suitable for use at frequendes up to 8 MHz, and as a mixer at low frequencies its performance is outstandng. The mixing is carried out by an operational multiplier package type XR2208. The circuit diagram of the receiver is shown in figure 1 and the following discussion refers to elements in that diagram.ДЇigure 1 VK5BR VLF-LF receiver circuit diagram (Refer also to fig 4 for BFO) The mixer stage All inductive elements are provided by stock lines of miniature RF chokes.Д«ecause of the low frequencies involved, it has been possible to use a number of excellent integrated circuit packages which would be unsuitable on the HF bands. The RF end is untuned and the receiver bandwidth is set by two inexpensive ceramic filters in the IF channel. Tuning is carried out by a potentiometer, the resistance of which sets the frequency of the heterodyne oscillator. It has no variable capacitors or inductors except for one preset trimmer in a trap circuit. The receiver design is a little different from the usual form. The VLF and LF bands have their own unique useful characteristics and these will be discussed further on. It has been designated a VLF-LF receiver, because it tunes the VLF-LF range from 10 to 300 kHz, but it also tunes part of the MF spectrum from 300 to 500 kHz. The superheterodyne receiver described is the result. Likewise, the writer had no receiver which could tune these frequencies and set out to design a simple receiver for just that purpose. Home - Techniek - Electronica - Radiotechniek - Radio amateur bladen - Amateur Radio - A VLF-LF receiver - 10kHz to 500 kHz with resistance tuningДЇew communications receivers tune to frequencies below 500 kHz and because of this, many radio enthusiasts are unfamiliar with this section of the radio frequency spectrum which supports numerous radio services.

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