# RF Downconversion using Heterodyne Principle

• 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?

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.

• 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? May 17, 2020 at 14:57
• if your frequency shift is amplitude preserving, then yes, amplitudes are preserved. May 17, 2020 at 21:17