How far can one communicate with low power or poor propagation? Some of the techniques employed to enable signals to be dug out from below the noise level are demonstrated in the projects listed here:

(CCW) Coherent CW – This is sent by computer with extreme precision and stability which allows matched comb filters to dig out the signal from the background in real time at up to 60 characters per minute.

(QRSS) Very slow CW – By using extremely slow generated CW it is possible to use a computer sound card and special software to extract CW characters from below the audible noise floor. Morse Code element lengths of 10 to 30 seconds (or even longer) per dot are commonly used.

(MEPT-JT) – This uses frequency shift keying (FSK) with a very small shift at a very slow and precise rate. The data is encoded to reduce the number of data bits needed, with the result that only standard call signs can be used – no prefixes, suffixes or special calls. Reed-Soloman encoding is employed to enable forward error correction to be used to improve the chances of copying even under adverse conditions. Each transmission lasts for just under two minutes, and starts at the beginning of each even-numbered minute.

(WSPR) Weak Signal Propagation Reporter – This is based on the MEPT-JT technology and is designed to probe potential radio propagation paths using low-power beacon-like transmissions and is ideal for assessing antenna performance. It uses tones with a length of 0,68 seconds. There are 4 different tone frequencies (4 frequency shifts), but the difference is minimal, only 1,46 Hz! hence they sound like a continuous tone. The overall bandwidth is only 6Hz. WSPR signals convey a callsign, Maidenhead grid locator, and power level using a compressed data format with strong forward error correction. The protocol is effective at signal-to-noise ratios as low as -28 dB in a 2500 Hz bandwidth. Most WSPR signals are 5 watts or less and have been received world wide. Receiving stations with internet access may automatically upload reception reports to a central database. The WSPRnet web site provides a simple user interface for querying the database, a mapping facility, and many other features.

The WSPR Screen
WSPR Net Map

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