The receiver is a two phase Direct Conversion receiver with 90 Degree Audio phase shift network, a 3 kHz LP audio filter on board and requires two RF Local Oscillator inputs in quadrature. See Links for full circuit description, modifications and sources for PCB's. On our prototype we implemented the W7ZOI audio pre-amplifier modification which improved Sensistivity and overall gain by a few dB and is well worth the effort. Understand that Rick is in the process of updating the R2 design and if you are contemplating building an R2 you may want to wait for Rick's new design. The AD9850 circuitry is almost as per Analog Devices datasheet.
Serial programming is used.
The cure is simply to press the mode switch button which will reset the IC's. We intend to investigate this again once pre-production boards are becoming available. This PCB contains the Microchip 16F84 Microprocessor and interfaces with the DDS synthesizer PCB, the LCD Frequency readout module, a keypad and the RF Preselector board. U5 provides an extra 8 outputs for future expansion but this is not implemented in the receiver. JP6 also is for future expansion and provides three inputs for the transceiver project, however this is also not supported by the current firmware.