WSPR-X – Weak Signal Propagation analysis on OS X
Around the world a network of weak-signal propagation analysis stations continuously probes the mysteries of the ionosphere. Using the WSPR digital mode, enthusiasts transmit and receive signals on all amateur bands 24 hours a day. Operating with power levels down to the milliwatt level, WSPR can be set to automatically transmit and receive signal reports which are then collected and analyzed to provide an overview of the current propagation characteristics on each band. Developed by Nobel Laureate Joe Taylor (K1JT), WSPR is another weak-signal digital mode designed for maximum propagation with minimum power. With a keying rate of approximately 1.5 baud and an occupied bandwidth of approximately 6Hz, WSPR can resemble an unmodulated carrier; however, careful analysis reveals a 4-level FSK with a tone separation of 1.4648Hz. The 110 second transmissions consist of a structured message with the sending station’s callsign, the 4-digit maidenhead locator, and a power level (dBm). Signals can be received and decoded with a minimum SNR of -28dB (2500Hz reference bandwidth). Although experiments have been done, WSPR is not designed as a QSO mode.
There is also a 15-minute version of WSPR known as slow mode WSPR or WSPR-15. WSPR-15 is even narrower than standard WSPR with a tone spacing of only 0.183 Hz. This narrow tone spacing is not as effective on HF, but rather is designed for use on the new 137kHz and 472kHz bands available in many countries. Sensitivity is a full 9dB better than standard WSPR, allowing reception with a minimum SNR of approximately -37dB but at the expense of a 15-minute transmission duration.
One of the real strengths of WSPR is the networked analysis tools available to the user. Analysis of reception reports and near-real-time propagation conditions is assisted by the worldwide WSPR receptions uploaded to the WSPRNet database (wsprnet.org). Using the site, you can check the current conditions on any band or review the reception reports of your own signal. More than just a measurement of who can hear your signal, these reception reports can show frequency drift, how well your signal is being received (SNR), or even can serve as a basic antenna radiation pattern tool by showing which direction your antenna radiates best. You can also analyze how well your station performs on each band by doing a mile-per-watt analysis. Using the tools on WSPRNet, I can state that my Inverted L antenna radiates best to the northeast toward Europe as well as to the south and southwest, but less well towards the northwest. Additionally, I have determined that this author’s personal best miles-per-watt record is a .1 watt transmission from Maryland being received in Australia on 30m for over 100,000 miles per watt. With nearly 200 million spots in the database, with nearly 200,000 added every day, the different ways you can use the data available on WSPRNet is only limited by your imagination.
As with WSJT-X, Joe Taylor has also migrated his existing WSPR software development to a new C++/Qt framework to help save development time and effort. This new software, known as WSJT-X is available as a standard .app file on OS X. Currently at v0.8 r3058, WSPR-X builds upon the previous WSPR software and is far from the beta build that the 0.8 version number may indicate. Installation does require some very basic command line work; it is all fully explained in the readme files, and only has to be done once. If you install WSJT-X at the same time, use WSJT-X’s instructions as there is an extra step for WSJT-X, but everything else applies to WSPR-X as well.
The OS X version of WSPR-X can be downloaded from http://www.physics.princeton.edu/pulsar/K1JT/wspr.html.