FM detector. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Nodes of amateur radio equipment
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UB5UG has developed an FM detector circuit based on three 2I-NOT elements.
The frequency-modulated IF signal is fed to the pulse shaper (inverter D1), and from it to the coincidence element D3 and to the inverter D2. when output 01 is logic low, capacitor C2 slowly charges through the input resistance of element D3. and when high - quickly discharged through D2. Thus, the front of the pulse from the output D1 arrives at the upper input of the element D3 according to the scheme with some delay in relation to the front of the pulse that came to the second input D3.
In this case, the duration of the pulses at the output of the detector is proportional to the front delay, and their constant component is proportional to the modulating signal.
If the average frequency of the IF signal is 500 kHz, capacitor C2 should have a capacitance of 50 ... 150 pF. With a smaller IF value, a capacitor with a larger capacitance is used. In any case, it must be selected so that the LF voltage is maximum.
In the FM detector, you can use, for example, the K155LAZ chip.
Author: UB5UG; Publication: N. Bolshakov, rf.atnn.ru
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