Updated 02/06/2024 by KD2ZWN

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.
• 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. WSJT, and WSPR have all been rolled into one program, WSJT-X, which is also the common program used for FT8 and FT4 transmissions.

General

• Weak Signal -- (VHF-DX, Meteor Scatter, EME-Moonbounce) (Radio Technology Topics, ARRL Web)

Coherent CW

• Coherent CW -- The Concept -- Part 1
  QST May 1981, pp. 11-14
  Would you think that you could decrease your transmitter output power by a factor of 10 and increase signal readability by the same amount -- simultaneously? It's being done now.
• Coherent CW -- The Practical Aspects -- Part 2
  QST June 1981, pp. 18-23
  You'll now see how you can put the concept into practice.
• A DSP Version of Coherent-CW (CCW)
  QEX February 1994, pp. 25-30
  Obtain the advantages of coherent detection of Morse signals using DSP.

WSJT and WSPR

• 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.

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 and WSPR

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