LPF in FM receiver

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.

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

To continue: It is always easier to process signals in baseband
(centered
around 0) than it is to process RF signals (due to the high sampling
rates
required).

Given that the bandwidth you are interested in is in the order of 100kHz
(typical of FM radio signals), it is easy to see why radio receivers are
designed the way they are.

On 02/11/2014 11:22 AM, Pablo F. Alonso wrote:

https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
A complex LPF is the same as a symmetric bandpass, when signals are at
baseband.

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Hi Aditya, Hi Pablo,

the multiples-of-carrier-frequency problem is being solved in hardware
(you can’t do this in software, since mixing is still analog domain).

Anyway, as Aditya explained, since you are processing baseband
signals, a lowpass is actually a bandpass (you might at least think of
it as such) from -f_c to +f_c.
You need to do this, because the FM receiver should only deal with the
signal in the interesting band.

Greetings,
Marcus

On 11.02.2014 17:35, Aditya D. wrote:

[email protected]wrote:

Let’s say you are trying to receive an FM signal centered around
MHz.
_______________________________________________ Discuss-gnuradio
mailing list [email protected]
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

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