Narrow Band FM 6 KHz width
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Total Band width of FM = 2 x ( Deviation + maxium modulated frequency ) , so 1.5kHz deviation with 1.3 kHz maimum modulated audio frequency should make FM about 5.6 kHz wide.
from normal Ham radio audio ( 300 Hz to 3KHz ), band pass with 1kHz to 2kHz filter, most of audio information are in this frequency range.
( audio .wav files link -> ) 300 Hz to 3Khz audio sound ( original ) --> ( band pass filtered ) 1kHz to 2kHz audio sound
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transpose ( pitch change ) that ( 1kHz to 2kHz ) audio to ( 300Hz to 1300 Hz )
( audio .wav files link -> ) transposed / frequency shifted audio sound ( 300 Hz - 1300 Hz ) ( it sort of sound like off tuned SSB signal ) , because it is same principle as off tuned SSB.
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transmit it using +/- 1.5kHz deviation FM, below 300Hz is for CTCSS and DCS
at receiver end , reconstract ( transpose ) back ( 300Hz - 1300Hz ) audio to ( 1000Hz - 2000Hz )
( audio .wav files link -> ) transpose up ( reconstructed sound ) back to 1kHz - 2kHz.
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below is daigram of above explanation.
2013-05-19