I am designing a FM radio receiver. Can anyone tell me show much power
can I receive from a FM station that is in a acceptable range? I need
that value to decide the gain of all the stages. Thanks.
Allen
Usually FM receivers are designed with excess gain, since there is no
need for amplitude linearity. You didn't say what sort of FM station
you want to receive. FM signals vary greatly in the bandwidth they
occupy: communications channels (police, fire, pagers, etc) are
typically only a few kHz wide, and FM broadcast is typically about
150kHz wide. That makes a difference: since you'll pick up about the
same amount of noise per unit bandwidth (atmospheric noise; galactic
noise; ...) for signals at approximately the same carrier frequency,
the total noise in the channel varies with bandwidth. So for wider
bandwidth, it takes more signal to rise above the noise and be
useable. A reasonable goal for FM broadcast at 100MHz would be to be
able to receive signals greater than -165dBm/Hz bandwidth, or about
-114dBm. That's about half a microvolt at 75 ohms, I believe.
You may wish to think about a bunch of other things before going very
far with your project: how will you avoid distortion from big signals
when you are trying to listen to small ones? How will you filter out
frequencies (channels) other than the one you want to listen to? How
will you maintain phase linearity so you achieve low distortion?
If you don't get discouraged along the way, and you keep your eyes and
mind open, you'll discover that there's a lot more to designing a good
receiver than initially meets the eye. And I want to make it clear
that I do NOT want to discourage you, because it's by doing things
like that that you will learn, possibly learn a whole lot.
Cheers,
Tom