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From: | Marcus Müller |
Subject: | Re: [Discuss-gnuradio] Stuck at WBFM Project : |
Date: | Tue, 8 Aug 2017 10:52:06 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 |
Hi Ash, This might be a bit of a DSP problem more than a GNU
Radio-specific one! So, you have what's meant to be 960 kHz, and then you interpolate it again, by 20, to a signal that is meant to be sampled at 19200 kHz = 19.2 MHz. Then you go ahead and "play back" that signal with a hardware device through the Osmocom sink, but at 8 MS/s – so, everything transmitted is played back at /less than half speed/! I don't really understand what your motivation with the specific
parameterizations of the two (that's definitely one too many)
resamplers, or the WBFM was, but you should probably just take a
step back, and ask yourself "what does this block do?" for /every/
block. This flow graph looks like it is a random combination of
tutorials and Youtube videos – that's not how engineering works
;). (By the way, there's other things wrong with the flow graph,
but since it needs a bit of restructuring anyways, I'm not going
to address those here) If you haven't, I'd strongly recommend reading the "Guided
Tutorial" on https://tutorials.gnuradio.org It doesn't specifically address the sampling rate confusion you were a victim of, but it does (hopefully) give you a bit of a feeling about what generally happens, so I think this is the very most time-efficient method of approaching GNU Radio. Hey, and keep up the good work! Starting into SDR is always a bit of a rocky path, because you need a threefold set of talents – Radio, Software, and Signal Processing. Don't be demotivated if things don't work right off the start! To help you with your application: Remember, a Resampler has a
non-1 (output rate)/(input rate) ratio. In case of the rational
resampler, that ratio is (interpolation)/(decimation) What about Wav File Source -> WBFM (audio rate 48k, quadrature rate 192k)
-> Rational Resampler (interp/decim=(Osmocom sink sampling
rate)/(192k)) -> Osmocom sink Best regards, Marcus
On 08/08/2017 04:55 AM, Ash SDR wrote:
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