Thank you so much for your support Gary!
Your feedback guided me to the state I am in: I am starting to understand GNUR
The cf-slider drives a 'vfo' (signal source block) and the mixer(and filter)
ensures that their is a baseband signal for the downstream demodulation proces.
Very interesting that this is possibile with software!
Thanks for the example!
Up to now i only used SDRsharp to look &listen at spectrum without using all
the functions.
Yes, I continue to play around and will look further at 'decimation' which pops
up everywhere in gnr. If I get stuck I reach out.
Thanks again!
Robert
Op zo 10 dec 2023 om 01:00 schreef Gary Schafer <schafer@site2241.net
<mailto:schafer@site2241.net>>:
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
<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