from http://www.scgroup.com/ham/wolf.html WOLF
WOLF (Weak-signal Operation on Low Frequency) is a proposed new signal format and protocol designed specifically for the LF bands. It can be used for beacons and for two way communication. Unlike existing formats, which are optimized for a particular S/N (and corresponding speed), WOLF can operate over a wide range of signal levels. For example, a WOLF beacon transmits a 15-character message repeatedly. If the received signal would be adequate for conventional CW, copy will be displayed in 24 seconds. At a level barely enough for 0.4 WPM QRSS, copy will appear within two minutes. Even if the signal is another 10 dB weaker, the message can still be received. It will take from 20 minutes to several hours, depending on the stability of the Tx and Rx. Of course, it is also necessary that the propagation path remain open over the required interval. I hope that WOLF will permit a QSO to be completed in an hour, if one station receives a signal that is 10 dB weaker than would be needed for QRSS, and the other station's signal is 6 dB below the QRSS threshold. I believe that it is also feasible to "hear" a LOWFER beacon across the Atlantic, during an overnight run (very accurate time and frequency control is required). At this time, I have implemented only a crude "off-line demo". In transmit mode, this command line program writes a .wav file which contains the specified message. A simulation is performed by mixing (using an audio editor) a small amount of this signal with a large amount of noise (recorded off the air or synthetic, as desired). The resulting file is read by the program in receive mode, and attempts to decode the message are made at various intervals. For an on-the-air test, the transmit output file is played (with a media player or editor), feeding the audio into an SSB transmitter. There are also various ways to drive a PSK transmitter. The receiving station records the Rx output as a .wav file, which is then supplied to WOLF for decoding. There have been a few successful WOLF transmissions; simulated results have also been quite encouraging. I used the procedure developed by Lyle Kohler; see his description and results <http://www.computerpro.com/%7Elyle/weaksigs/weaksigs.htm>. Lyle's tests found that conventional CW could be received with the signal attenuated up to 18 dB below the reference noise level. For 0.4 WPM QRSS, the limit was -30 dB. BPSK at MS1000, ET1 was the most robust mode tested, showing intermittent copy after many minutes at -33 dB. WOLF occasionally shows good copy at -45 dB, and seems quite robust at -40. -- --------------------- and http://www.mlecmn.net/~lyle/wolf/wolf4beginners.htm WOLF for beginners -------------------------------------------------------------------------------------- Andy K3UK
