Decoding unstable FSK modulated signals.
When a phase locked loop (PLL) is used for decoding FSK (frequency shift keying) modulated signals its output is very sensitive to even slight changes of the ''mark'' and ''space'' frequencies which-by international convention-are rather close together. The use of a nonstandard circuit around the PLL can improve greatly its ability to properly decode distorted or poorly modulated FSK signals.
Richner
H
H
Federal Institute of Technology, Laboratory for Atmospheric Physics, CH-8093 Zurich, Switzerland.
Phillips
P D
PD