Hi Carlo, not quite sure I get what you mean with "bandlimiting"? What with "transposing"?
Regarding "padding": do you mean interpolation? Again, you'd use a resampler, and in your case, the rational resampler with decimation=1, interpolation = 48 would do the trick. Best regards, Marcus On Mon, 2018-06-04 at 22:09 +1000, Carlo Manfredini wrote: > Thank you for your detailed reply. > I've taken a look at those links and for now are having some success > using the Clock Recovery MM block with default settings (and 24 > samples/symbol) to capture the data at 2kbps...followed by a Bit > Slicer. > > After I modulate this 2kbps bit stream to 4-QAM I have a complex > 1kSymbol/s stream...as a data stream...with bandlimiting from the QAM > block. > > Can you suggest how I can pad this out so that I can output it from > my 48kSps DAC device such that it is output at a real rate of > 1kSymbol/sec ? > > Ive tried out "repeat" blocks but without any significant progress. > > What is the best approach for this situation of having to transpose a > data stream to a specific output rate ? > > Regards. > > > > > > On 1 June 2018 at 22:25, Andy Walls <[email protected]> > wrote: > > > From: Carlo Manfredini > > > Date: Fri, 1 Jun 2018 21:24:26 +1000 > > > Hello, > > > I have a 2kbps bipolar data stream (in hardware) which I will > > sample > > > at 48kSps and bring into GR. > > > Once in GR, I wish to be able to sample only once per bit...so I > > use > > > the "Keep 1 in N" block (where N=24) and this reduces my rate to > > > 2kSps...with 1 sample per original data bit. > > > > > > However, I wish to be able to control exactly at which point in > > the > > > 48kSps stream that I sample down to 2kSps. > > > > > > This is equivalent in hardware terms to being able to select at > > which > > > point in each bit period that I sample once per bit.ie: selecting > > the > > > decision point in an eye pattern). > > > > > > The reason for this process is that I simply wish to read in the > > > original 2kbps bit stream so that I can use this data to do some > > PSK > > > modulation in GR etc...but my inputting device only runs at > > 48kSps. > > > > > > Is there some way with existing GR blocks that I can tell where > > > abouts in the 48kSps stream that I have actually sampled ? so > > that I > > > can manually set this sampling point. > > > > This is precisely the function of the Symbol Synchronization > > blocks. > > > > https://www.gnuradio.org/wp-content/uploads/2017/12/Andy-Walls-Samp > > les-to-Digital-Symbols.pdf > > > > You should play with the example here: > > > > https://github.com/gnuradio/gnuradio/blob/master/gr-digital/example > > s/demod/symbol_sync_test_float.grc > > https://github.com/gnuradio/gnuradio/blob/master/gr-digital/example > > s/demod/symbol_sync_test_float_ted_gain.m > > > > > > You'll probably want to do something like: > > > > -> Decimating FIR filter -> FIR Filter -> Symbol Sync -> Binary > > Slicer -> > > > > The first decimating FIR filter would anti-alias filter and > > downsample > > by, let's say, 2 or 4, to bring the stream down to either 12 or 6 > > samples per symbol. > > > > The second FIR filter would be a pulse matched filter, to get rid > > of > > noise and peak the symbol centers. (You can merge this filter into > > the > > previous filter, if you want.) > > > > The Symbol Sync block estimates the exact symbol centers, and > > downsamples to just those sample points. > > > > The binary slicer just thresholds its input samples to give you 1 > > or 0 > > valued samples on output. > > > > > Perhaps a simpler question is : how do I know where the "Keep 1 > > in N" > > > block is sampling ? > > > > You don't. > > > > Regards, > > Andy > > > > > Thanks for any hints...hopefully I have explained this > > adequately. > > > > _______________________________________________ > Discuss-gnuradio mailing list > [email protected] > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
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