Figure 1: Top side and underside view of one of the low cost Chinese AD9850 DDS modules DDS What is direct digital synthesis? DDS chips output digitally generated sine waves at frequencies from near-DC to several GHz depending on the particular device you use. Before long, several of these modules had arrived on my bench. And these modules came complete with the required reference crystal oscillator and a low pass filter. Just a few dollars each, perhaps less than one-tenth what the chip alone used to cost. ![]() These modules use one of the more common DDS chips, the Analog Devices AD9850, and were available at an incredibly low price. ![]() Browsing across the Internet one day, I stumbled across a reference to (at that time) a recently released Chinese DDS module. Introduction Temptation is a powerful thing. A DDS VFO for the Lydford 40m QRP SSB Transceiver Combining a very cheap Chinese-made DDS module and a low cost microprocessor and LCD display, this VFO delivers band-wide tuning, digital stability and four tuning speeds to the Lydford transceiver.
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