We report on the frequency performance of a low cost (~500$) radio-frequencysine wave generator, using direct digital synthesis (DDS) and afield-programmable gate array (FPGA). The output frequency of the device may bechanged dynamically to any arbitrary value ranging from DC to 10 MHz withoutany phase slip. Sampling effects are substantially reduced by a high samplerate, up to 1 MHz, and by a large memory length, more than 2.10^5 samples. Byusing a low noise external oscillator to clock the DDS, we demonstrate a phasenoise as low as that of the master clock, that is at the level of -113dB.rad^2/Hz at 1 Hz from the carrier for an output frequency of 3.75 MHz. Thedevice is successfully used to confine an ultracold atomic cloud of rubidium 87in a RF-based trap, and there is no extra heating from the RF source.
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