Hi Andy,
> So if i want to have a sine with frequency 1 hz and 256 samples per
> sine period i have to set samplerate to 256 ?
>
> 1hz = 256/256
yes, this is DSP, so all we care about is rates relative to the sampling
rate. I got into the habit of thinking of the sampling rate as always
being "1", and then your sine has a frequency of 1/256, ie. it takes 256
samples for a full period.
> The head block has 2 parameters: number of items, vector length
The signal source spits out single samples, so your vector length is 1.
> Now this is non specific gnuradio question, but how is it possible
> with python to create a sine with 1 hz from this lookup table.
For any frequency of sines you'd want to generate, you'd advance at a
speed of len_of_table*relative_frequency. Think of it as this -- if a
sine that is generated by taking every sample from your table one after
the other has frequency f_sample/256, then the sine of twice that
frequency has every second sample, and so on.
> My first idea is: python has to sample the 256 samples (for one
> period) from lookup table in exactly one second. So i think i need a
> timer which calls the next sample in the lookup table all 3,9 ms.
no!
GNU Radio is *NOT* a system where samples are processed
sample-by-sample, with a fixed precise sampling rate. Each block is just
asked to process/generate/sink as many samples as possible, and the
result is passed on to the next block as fast as possible.
Best regards,
Marcus
On 12/26/2015 05:28 PM, Andreas Ladanyi wrote:
> Hi Marcus,
>> Well, first:
>> Signal Source can't produce 8bit signed integers by itself, so you'll
>> have to convert whatever you configure the signal source for to char,
>> eg. you could set it to "float" and use the "float to char"
>> conversion. Make sure the result has amplitude 127. Properly
>> configure your signal source for the desired sine period, e.g.
>> sample_rate=X , frequency = X/256.
> So if i want to have a sine with frequency 1 hz and 256 samples per
> sine period i have to set samplerate to 256 ?
>
> 1hz = 256/256
>>
>> Then, use a "head" block with that period, and pipe the result to a
>> file sink; use the char/byte type of everything. Done. Pretty
>> straightforward, I guess :)
> The head block has 2 parameters: number of items, vector length
>
> The number of items is the amount of samples for a sine period = 256
> in this case ?
>
>>
>> As a side note: that's really a bit of a corner use case; a single
>> line of python would probably be easier:
>>
>> import numpy
>> (numpy.sine(numpy.linspace(0,2*numpy.pi,256)) *
>> 127).astype(numpy.int8).tofile("/tmp/sinetable.dat")
> This works perfect. Now i have a table with one sine period.
>
> Now this is non specific gnuradio question, but how is it possible
> with python to create a sine with 1 hz from this lookup table.
>
> My first idea is: python has to sample the 256 samples (for one
> period) from lookup table in exactly one second. So i think i need a
> timer which calls the next sample in the lookup table all 3,9 ms.
>>
>> in C, that program wouldn't be much longer.
> and maybe faster ?!
>>
>> Best regards,
>> Marcus
>>
> regards,
> Andy :-)
>
>
>
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