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To further add to John Rennie's answerJohn Rennie's answer: you don't even need autotuning for a frequency drift of the magnitude John calculates (10Hz): all FM receivers I've ever dealt with (I qualified as an electrical engineer in 1985 and worked a few short years in communications before returning to study) demodulated with a phase locked loop detector, whose job it is to follow drifts in the carrier frequency like this.

In any case, in any FM demodulation, a constant 10Hz offset decodes to a very small DC (*i.e.zero hertz constant offset) signal: let's say the full dynamic range corresponds to $10^5Hz$ as in John's answer, this offset is 80dB down on the demodulator's full dynamic range. The fully demodulated signal probably doesn't reproduce signals down to DC anyway. Your car's speed cannot change quickly, so variations in its speed would correspond to a variation in this offset with a frequency of a hertz or so maximum: if it gets through the full demodulation filter at all, it's going to have negligible effect on the signal.

To further add to John Rennie's answer: you don't even need autotuning for a frequency drift of the magnitude John calculates (10Hz): all FM receivers I've ever dealt with (I qualified as an electrical engineer in 1985 and worked a few short years in communications before returning to study) demodulated with a phase locked loop detector, whose job it is to follow drifts in the carrier frequency like this.

In any case, in any FM demodulation, a constant 10Hz offset decodes to a very small DC (*i.e.zero hertz constant offset) signal: let's say the full dynamic range corresponds to $10^5Hz$ as in John's answer, this offset is 80dB down on the demodulator's full dynamic range. The fully demodulated signal probably doesn't reproduce signals down to DC anyway. Your car's speed cannot change quickly, so variations in its speed would correspond to a variation in this offset with a frequency of a hertz or so maximum: if it gets through the full demodulation filter at all, it's going to have negligible effect on the signal.

To further add to John Rennie's answer: you don't even need autotuning for a frequency drift of the magnitude John calculates (10Hz): all FM receivers I've ever dealt with (I qualified as an electrical engineer in 1985 and worked a few short years in communications before returning to study) demodulated with a phase locked loop detector, whose job it is to follow drifts in the carrier frequency like this.

In any case, in any FM demodulation, a constant 10Hz offset decodes to a very small DC (*i.e.zero hertz constant offset) signal: let's say the full dynamic range corresponds to $10^5Hz$ as in John's answer, this offset is 80dB down on the demodulator's full dynamic range. The fully demodulated signal probably doesn't reproduce signals down to DC anyway. Your car's speed cannot change quickly, so variations in its speed would correspond to a variation in this offset with a frequency of a hertz or so maximum: if it gets through the full demodulation filter at all, it's going to have negligible effect on the signal.

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Selene Routley
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To further add to John Rennie's answer: you don't even need autotuning for a frequency drift of the magnitude John calculates (10Hz): all FM receivers I've ever dealt with (I qualified as an electrical engineer in 1985 and worked a few short years in communications before returning to study) demodulated with a phase locked loop detector, whose job it is to follow drifts in the carrier frequency like this.

In any case, in any FM demodulation, a constant 10Hz offset decodes to a very small DC (*i.e.zero hertz constant offset) signal: let's say the full dynamic range corresponds to $10^5Hz$ as in John's answer, this offset is 80dB down on the demodulator's full dynamic range. The fully demodulated signal probably doesn't reproduce signals down to DC anyway. Your car's speed cannot change quickly, so variations in its speed would correspond to a variation in this offset with a frequency of a hertz or so maximum: if it gets through the full demodulation filter at all, it's going to have negligible effect on the signal.