| 摘要 |
<p>A problem arises in attempting to recover low frequency FM components in receivers using wide bandwidth tracking loops. Wide loop bandwidths are desirable for rapid signal acquisition but interfere with demodulation of low frequency FM components, such as those produced by digital signalling data. This invention permits recovery of the full modulation spectrum with flat frequency response. A conventional FM demodulator (15) recovers the high frequency modulation components; the frequency control signal for the local oscillator (3) provides the low frequency components. Combining (35) the components with proper weighting (31, 33) produces recovered modulation (37) with bandwidth limited only by the IF bandpass filter (7) or demodulator. The invention would find application in an FM receiver of the superheterodyne or direct conversion type that requires precise frequency control, such as one used for communications in a narrow channel spacing environment at ultra-high frequencies.</p> |
