Re: [Discuss-gnuradio] low frequency in GRC

[Activecat]

On Fri, May 16, 2014 at 2:01 AM, Marcus Leech <address@hidden> wrote:

Gnu Radio is a streaming architecture. Sample-rate is actually almost-entirely meaningless within the flowgraph, and only really

  has meaning "at the edges" when interfacing to the real world.  The only exception is the throttle block, and even it doesn't

  produce *precise* sample-rates.

A too-low value of sample-rate (samp_rate) could be hazardous.

For example, in Jason's flowgraph attached in his previous email, the settings of the Signal Source block are:

  - Sample Rate = 100

  - Frequency = 50

  - Signal Type = Saw Tooth

In this case the output from this block is just a repeating of two float numbers:-   0.5,  0.0, 0.5,  0.0, 0.5,   0.0, 0.5,  0.0, 0.5,  ....

If the Sample Rate is reduced to 50, then the output becomes a constant value:- 0.5,  0.5,  0.5,  0.5, ...   (this is worse).

If "Saw Tooth" is the signal pattern that he really wants out from this Signal Source block, then he needs to set the sample-rate to a high-enough value, for example, samp_rate=1000. With this value the Signal Source block will produce output which looks more like Saw Tooth:-

0.50,  0.55,  0.60,  0.65,  0.70,  0.75,  0.80,  0.85,  0.90,  0.95, 
0.00,  0.05,  0.10,  0.15,  0.20,  0.25,  0.30,  0.35,  0.40,  0.45,  0.50,  0.55,  0.60,  0.65,  0.70,  0.75,  0.80,  0.85,  0.90,  0.95, 
0.00,  0.05,  0.10,  0.15, .................

Hence, the value of samp_rate does make a significance in the flowgraph.