Today both the 9 cm and the 13 cm OZ7IGY beacons have been migrated to the Next Generation Beacons platform http://www.rudius.net/oz2m/ngnb
The 9 cm and 13 cm beacon are now frequency and time locked to GPS. The sequence is timed to start at 00 second sending PI4 followed by a short pause then CW ID sending callsign and locator, then pause and carrier until next cycle. The nominal frequency remains the same, i.e. 2320,930 MHz and 3400,930 MHz respectively. To decode PI4 tune your receiver to 800 Hz below the nominal frequency, just like you do when you want to decode a normal CW signal at 800 Hz. On most radios this is a USB dial of 2.320.929.200 for the 13 cm beacon and 3.400.929.200 for the 9 cm beacon
The 13 cm beacon uses a combination of the Super Nyquist principle per Analog Devices AN-939 paper and a frequency doubler of the signal from the AD9912 DDS. The 9 cm beacon signal comes from a x9 frequency multiplication of the AS9912 DDS output.
PI4 is a digital modulation (MGM) specifically designed with beacons and propagation studies in mind.
PI4 decoder download: http://www.rudius.net/oz2m/software/pi-rx
PI4 encoding examples in Arduino C, Atmel C, Delphi Pascal, Microsoft Visual Basic and Microsoft C++: http://www.rudius.net/oz2m/ngnb/software.htm
PI4 online encoding and frequency calculation: http://www.rudius.net/oz2m/ngnb/pi4encoding.php
PI4 specification: http://www.rudius.net/oz2m/ngnb/pi4.htm PI4 is a cousin of JT4, JT9 and WSPR.
OZ7IGY homepage: http://www.oz7igy.dk