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Weak Signal Modes


Amateur Radio operators normally operate at power levels much below commercial broadcasters, even with our 1.5 kW maximum power level.  Many hams like to operate QRP (5 watts or less) and still get very good signals when band conditions are right.  How far can we go to communicate with low power or poor propagation?  Several projects use advanced circuit and software techniques to allow you to dig signals out that seem to be well below the noise level.

  • Coherent CW is a technique that employs stable and precisely calibrated transmitters keyed at a known "clock rate".  This allows receivers to use extremely narrowband filtering that increases the signal to noise ratio to a usable point, even if the sending rate is very slow.
  • QRSS is a very slow speed (QRS) CW mode, designed to be used with narrowband filtering, but it is not based on signal coherence. 
  • WSJT and WSPR are special digital weak signal modes developed by ham radio's own Nobel laureate, Joe Taylor, K1JT.  WSJT (Weak Signal - Joe Taylor) mode provides several modes optimized for meteor scatter, troposcatter, or EME (Earth - Moon - Earth, moonbounce) communication.  WSPR (Weak Signal Propagation Reporter, "whisper") is designed to monitor propagation paths on the MF and HF bands.  In 2018 FT8 is an extremely popular HF mode.



Coherent CW


  • A DDS Based QRSS (and CW) Beacon, Matteo Campanella, IZ2EEQ
    QEX, Sep. 2007 p 24
    Letter: QEX, Nov 2007, p 60


  • WSJT: New Software for VHF Meteor-Scatter Communication 
    Joe Taylor, K1JT, QST December, 2001, pp. 36-41
    With this revolutionary software you can communicate over distances up to 1400 miles by bouncing signals off the ionized trails of ... tiny meteors.
  • The Accidental EME QSO 
    Dave Scroggins, W7OJT, and Mike Hasselbeck, WB2FKO, QST November 2005, pp 52-53
    While trying to set up a tropo scatter contact, the authors instead discover EME!


Web Links

Coherent CW

  • Coherent CW: Some Theory, Ernst F. Schroeder, DJ7HS
    CCW is not magic, it is just the application of well-known pieces of communication theory
  • The CCW Archives Maintained by N2APB, with permission from the original CCW archive owner Bill McClune, N3REY



  • WSJT Home Page
    Current information and downloads for WSJT, WSPR, and related software.
  • WSPRnet
    Blog and real-time monitor of WSPR propagation reports.