Re: [Discuss-gnuradio] LPF in FM receiver

[Aditya Dhananjay]

In the FM receiver: Why a LPF is used instead of a BPF in order to select the Radio channel that we want to hear? That is the only part I don't understand.

Hello Pablo,

Let's say you are trying to receive an FM signal centered around 100MHz. In other words, the signal of interest is from (100-delta)MHz through (100+delta)MHz.

My understanding is that at the receiver, you are first demodulating the signal by multiplying the incoming signal with the carrier frequency of 100MHz. This leads to two bands:

a) Centered around 0: (-delta through +delta)

b) Centered around 200MHz: (200-delta) Mhz through (200+delta) MHz.

Signal (a) is what you are interested in, while signal (b) needs to be eliminated. This is where the LPF comes in.

Best,

Aditya