- after a RF down-conversion using heterodyning principle, will there be an information loss?
- If we translate to a fixed IF frequency, is there is an intuitive way of explain that the information can be retrieved?
- Is it correct to say that it is the relative change that matters during demodulation?
- For example for AM it is the amplitude change and for FM its frequency change and this does not change even if we down-convert to a fixed IF frequency?
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after a RF down-conversion using heterodyning principle, will there be an information loss?
No, if the original signal was band-limited, and the bandwidth of your IF processing is sufficiently large to capture that. (so, if you've built a sensible heterodyne receiver.)
If we translate to a fixed IF frequency, is there is an intuitive way of explain that the information can be retrieved?
Yes. Shifting a frequency is just multiplications with $e^{j\Delta_f t}$, and that's an easily invertible operation (multiply with $e^{-j\Delta_f t}$).
If an operation is perfectly invertible, no information was lost.
Is it correct to say that it is the relative change that matters during demodulation?
I don't understand that sentence, but I think you really mean "what matters is the bandpass content, not the carrier frequency", and that would be right. See: equivalent complex baseband.
For example for AM it is the amplitude change and for FM its frequency change and this does not change even if we down-convert to a fixed IF frequency?
This depends on how you do the AM and FM demodulation – if they work the same no matter the carrier frequency, then clearly yes.
answered May 17, 2020 at 9:40
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$\begingroup$ Hi Marcus, Thank you very much for the reply. Regarding to the 3rd question I asked For example: I have a receiver with fixed IF 15 MHz. All the frequencies are down-converted to this frequency. If I have an AM signal at 100 MHz and a FM signal at 80 MHz, centre of these frequencies will be shifted to 15 MHz, bandwidth remains the same. Now for AM case, even though frequencies are down-converted, amplitude variations still remains the same. Similarly, for FM, frequency change remains still the same. Which means we can retrieve the information. Is this explanation correct? $\endgroup$– radar101May 17, 2020 at 14:57
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$\begingroup$ if your frequency shift is amplitude preserving, then yes, amplitudes are preserved. $\endgroup$ May 17, 2020 at 21:17