Information about the sampling rate of the RTLSDR driver

Leif Asbrink leif at sm5bsz.com
Mon Dec 17 13:52:48 UTC 2012


Hello Frederic,

Each sample is I and Q with 8 bit each. That is 2 bytes.
When you sample at 2.048 Ms/s you get 4096 bytes/ms so your
observation that it takes 2 ms to fill the buffer is fine:-)

The buffer size is not critical. In my project Linrad it is
a user parameter because small buffers may be useful for
radio amateurs who want a small delay from antenna to
loudspeaker when doing two-way communication while larger
bufers may be helpful on slower computers.

I tried buffers from 2048 bytes to 524288 without errors
on a fast computer.

You are not doing anything wrong:-)

Leif


> Hello,
> 
> I am testing a DVB-T USB key including the Elonics E4000 chipset and I want to check the sampling rate of this card.
> I set up the sampling rate at 2.048 Ms/s (rtlsdr_set_sample_rate), and my storing buffer is 8*1024 bytes, so I expect receiving 1024 I/Q samples every 500 microseconds.
> I am using the rtlsdr_read_async function to read the samples.
> Unfortunately the loop in my program indicates that 8*1024 bytes are read every 2 milliseconds.
> I am using the gettimeofday function to measure the time in microseconds.
> Does this result mean that the best I can do is to read some samples every 2 ms at 2.048 Ms/s. This would mean that I am missing 1.5 ms of signal.
> Is that correct or I am doing something wrong ?
> 
> Thanks for your help.
> Frederic
> 
> 
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