In article , "Richard"
writes:
Dr. A.T. Squeegee wrote:
In article ,
says...
Hi. Anybody developed a nbfm RX project covering the FM band (appx
87.5Mhz-108Mhx).
NBFM? As in narrow band?
What would be the point? Here in the U.S. at least, that entire
band is assigned to FM broadcasting, and it is anything but narrow-band.
Typical deviation from a broadcast station is 75+ kHz.
Maybe I used the wrong term. I think lots of HiFi tuners have very wide
filters much greater than 75 Khz. For DXing it seems then you need no more
than say 75Khz. A tuner with that bandwidth would, in a sense, (Ithink)
compared to a regular HiFi tuneer be a narrow bandwidth tuner.
BTW, what would be the result if you used say a 20Khz filter on a FM signal
with 75 Khz deviation? Would you get distortion or a perfectly copyable
signal. I mean is it the analagous to using a 2Khz filter for an AM signal
transmitted at 6Khz wide?
You need to refresh your personal databanks on basic modulation.
In FM the modulation amplitude "swings the frequency up and down
in frequency." [close and simplistic, there's a bit more to it...]
Limiting the bandwidth of the receiver is the same as clipping the
peaks of an amplitude modulation. You WILL get a LOT of
distortion on high-amplitude modulation input at a station.
In a limited-bandwidth AM receiver there is no limit on the amplitude
of an AM signal, just the frequency range of the modulation signal.
In a limited-bandwidth FM receiver there is both a limit on the
amplitude and frequency range of the modulation signal.
Len Anderson
retired (from regular hours) electronic engineer person