Re: Hello World for WBFM Wav-file source?

[Gary Schafer]

Okay, now that the wife has her Christmas tree, I have some time to look at 
your flowgraph.

Already mentioned that your sample rate was incorrect, and that you needed to 
shift the frequency of the signal.

Let's start with the sample rate. You understand the basics. That much is 
clear. If the sample rate of the file was 2 MHz, then it appears that 
everything would have been correct, with one exception. You had your lowpass 
filter set with a transition width of 1 MHz. (Did you happen to get that from 
the Hak5 video on Youtube, by any chance?) It should only be 10 kHz - 30 kHz. 
I'm using 20 kHz in your revised flowgraph. But with the sample rate set 
incorrectly, that throws off everything. The filter will not work properly, nor 
will any of the other blocks that use the sample rate.

Next, the signal wasn't centered. I'm guessing that, when you recorded the IQ from SDRsharp (a good 
program, by the way), the signal was not centered. Maybe you had it set to "free tuning"? 
That's where you can simply click on the signal in any part of the spectrum you can see and it 
automagically demodulates it for you. What it is *actually* doing (and the part you don't see) is 
that it is centering the signal (doing a frequency shift), THEN filtering and demodulating. I added 
a "Range" block to allow you to tune through the different signals. The other one should 
be at -100. (BTW, the way you recorded the higher frequency signal has a refrain that almost loops 
perfectly!)

Link to the corrected flowgraph: 
https://www.dropbox.com/scl/fi/hkv58onl1sfgquzk6xyml/SUCCESS_WBFM_Play_from_rtlsdr_file.grc?rlkey=2ybi78bh0wqjgbzq86a0r96sv&dl=0

Let me know if you need anything else!

Gary