Testing the AFC of linrad
Details of locking to a weak signal
For normal operation during contests a processing delay of 3
seconds is perfectly ok.
Figure 1 shows how the UNKN422.WAV file is received with an AFC
averaging time of 4 seconds with 25% delay.
The waterfall is zoomed in to show only the range 480 to 670Hz.
The baseband filter bandwidth is set to about 20Hz and the
baseband graph shows that the carrier as well as both principal
keying sidebands are within the filter bandwidth.
A somewhat weaker signal from an audio signal generator at 630Hz
is smeared out since the AFC follows the drifting EME signal.
The bandwidth of the first fft is 20Hz and the bandwidth of the
second fft is 5Hz.
Fig.2 is the same sequence when the AFC is locked to the audio
The afc graph shows that the audio generator is close to the limit
where locking is possible with these processing parameters.
The EME signal is 6 to 10 dB stronger and smeared out over the
frequency range it is drifting over.