For SDR Radio, I recommend a phase noise generator as the LO. A good sheterodyne provides a high signal-to-noise supply sensitivity of the receiver, as well as stability of operation and frequency. The ideal solution is DDS, which has a low noise level, fast frequency agility. The best options are the AD9910 (DDS9910) and AD9959 (DDS9959), the latter has 4 synchronized outputs.
DDS AD9959 Arduino Shield RF Signal Generator 4 Synchronized Channels DDS 225MHz, Low Spurs 600MHz
DDS AD9910 Arduino Shield Signal Generator 600 MHz @ 1.5GHz AM FM SSB Sweep, Low Spurs Low Harmonic