rtl_fm problem with capture audio

keenerd keenerd at gmail.com
Thu Nov 15 00:25:01 UTC 2012


On 11/14/12, Adam Nielsen <a.nielsen at shikadi.net> wrote:
> I think it's because it tunes to an offset, to avoid the centre spike.
> The frequency you use on the command line is what is actually decoded.
>
> I thought this is what the -E option was for, but WBFM reception sounds
> really bad when I use -E.

Correct on the offset.  -E is something else entirely though.  When
you are working with waterfalls, it is very easy to see the
center/carrier and estimate the bandwidth.  But usually radio
transmitters report their frequency as the lower edge of the spectrum.
 -E is for tuning this way.

So, lets say I have a NBFM transmitter tuned to 80MHz with 12kHz
bandwidth.  If you look at it on the waterfall, you will see the
carrier centered on 80.06MHz.  You could tune to it with either

-f 80e6 -s 12e3 -E
-f 80.06e6 -s 12e3

Both of those do the same thing.  -E can save some typing but center
tuning is easier if you don't know the bandwidth in advance.

With WBFM this all falls apart, because they use 200kHz of bandwidth
(stereo and digital modes) but are offset 16kHz from their official
frequency.  (Because at one point wbfm was mono with 32kHz of
bandwidth.) Use -W for wbfm, it takes all that into account.

-Kyle
http://kmkeen.com




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