Standalone Si570 based multiband WSPR beacon
The following is a minimalistic design of a standalone MEPT beacon used for WSPR broadcasts. It is based on a Si570 programmable crystal oscillator (silabs.com) which is controlled by means of an AVR attiny45 microcontroller. The Si570 device is FSK modulated by the AVR via a sequence of I2C control commands that are sent to slightly change the frequency for every transmitted WSPR symbol, allowing multiband operation on frequencies like:
3.5926MHz, 5.2872MHz , 7.0386MHz, 10.1387MHz,
14.0956MHz, 18.1046MHz, 21.0946MHz, 24.9246MHz,
28.1246MHz, 50.293MHz, 144.488MHz.
The Si570 device outputs a power of about 10mW which is already sufficient for WSPR operation, a small BS170 based power amplifier can be added to increases the power up to 500mW.
The beacon can be based on the foundation of existing kits such as USB Synth, FA-SY1 and SoftRock Ensemble Receiver or Transceiver Kit. Note when downloading the si570wspr_r20100922.ppt file, it must be renamed to si570wspr_r20100922.zip in order to be able to view the contents.
Note that the hex. representation of fuse setting in the document are wrong, they should be: highbyte=0x5d and lowbyte=0xef