SM 5 BSZ - Normal AFC parameters at 20Hz bandwidth..
(July 29 2001)

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 signal generator. 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.

Fig 1. AFC locked to UNKN422.

Fig 1. AFC locked to the reference signal at 630Hz.
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