Figure 1: Two “homemade” devices, both can receive wx faxes.
A few notes about using FlDigi software:
Set the shortwave receiver mode switch to USB (upper sideband) – and tune 1.9 KHz lower than the NOAA advertised broadcast frequency. Select OpMode -> WEFAX -> IOC576 from the main menu, adjust the sound card gain to optimize reception (use alsamixer on Linux) – and away you go!
The AFC control (in the lower right corner) will work well only with relatively strong stations. This automatic frequency control feature will need to be turned on or off depending on conditions. Roughly half of my received faxes are accomplished with this control in the “OFF” position.
Occasionally the slant control will have to be adjusted to straighten the fax as it is received.
The FlDigi software (open sourced and available at http://www.w1hkj.com/) is shown in figure 3, receiving a facsimile from the New Orleans US Coast Guard 4 KW transmitter. The top half experienced some interference, while the bottom seems to be a pretty good result. Note the signal in the waterfall (extreme bottom) – and its relatively decent strength, normally good for a nice fax plot.