High-Performance Shortwave Converter Circuit

Posted on Apr 9, 2012

The NE602 chip, Ul, contains oscillator and mixer stages. The mixer combines the oscillator signal with the input RF signal to produce signals whose frequencies are the sum and difference of the input frequencies. For example, an 8.5-MHz oscillator and a 10-MHz incoming signal will give output signals at 18.5 MHz (10 + 8.5) and 1.5 MHz (10 - 8.5). Recall that 1.5 MHz is 1500 kHz and an ordinary AM radio will tune to it.The choice of crystal depends on what shortwave band you want to hear. The 9.5- to 10-MHz band is less crowded and includes the time-signal station WWV. For that band, you`ll need a crystal of 8.5 to 8.9 MHz. There is no standard microprocessor crystal in that range, but you can use an amateur radio crystal, have a crystal custom-made, or use a CB crystal.

High-Performance Shortwave Converter Circuit

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Transformer Tl rejects signals that are outside the band you are interested in. Transformer T1 should pass signals from 9 to 11 MHz and attenuate all others. The transformer, Tl, used in the circuit is a 10.7-MHz IF transformer salvaged from an FM radio. They are fairly easy to obtain new from parts stores and mail-order houses. Most 10.7-MHz IF transformers will tune across the 9.5- to 10-MHz band without modification; all you need to do is turn its tuning slug. To receive the 6.0- to 6.5-MHz shortwave band, you`ll have to add a 150-pF capacitor. * Capacitors CI 150-pF, ceramic disc (see text) C2 32-pF, ceramic disc C3, C5 220-pF, ceramic disc C4 0.04 or 0.05-, ceramic disc Additional Parts and Materials Ul NE602N frequency-converter integrated circuit, D1 6.2-V, 0.4 or 1-W Zener diode, R1 10,000-ohm panel-mount potentiometer, R2 1000-ohm, W, 5% resistor, Jl, J2 RCA phono jack, SI DPDT, toggle switch, panel mount, Tl 10.7-MHz IF transformer (green color coded), XTAL 1 8.5-MHz crystal or CB channel-5 receiving crystal (see text), XTAL 2 5.0-MHz microprocessor crystal for 6-MHz band

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