Signal Source

From GNU Radio
Jump to navigation Jump to search

Signal generator: generates a variety of waveforms.

Supports an output of type complex, float, int, and short


(R): Run-time adjustable

Sample Rate (R)
Default value: samp_rate
Sample rate (fs) is the average number of samples obtained in one second. Its units are samples per second or hertz e.g. 48,000 sample rate is 48 kHz.
Waveform (R)
options: [Constant, Sine, Cosine, Square, Triangle, Saw Tooth]
Description: see "Waveform Types" below
Frequency (R)
Frequency of the waveform (default: 1000)
Amplitude (R)
Amplitude of the output (default: 1)
Offset (R)
Offset from zero (default: 0)
Initial Phase (Radians) (R)
Default: 0

Waveform Types

A constant value as specified by Amplitude + Offset
Real-valued signal types: Amplitude·sin(2π·Frequency/Sample Rate·n) + Offset
Complex-valued signal types: Amplitude·[cos(2π·Frequency/Sample Rate·n) + 1j·sin(2π·Frequency/Sample Rate·n)] + Offset
Real-valued signal types: Amplitude·cos(2π·Frequency/Sample Rate·n) + Offset
Complex-valued signal types (identical to Sin): Amplitude·cos(2π·Frequency/Sample Rate·n) + 1j·sin(2π·Frequency/Sample Rate·n) + Offset
Square (Phase wraps in [–π,+π], increasing by Frequency/Sample Rate every sample)
Real-valued signal types:
phase < 0: Amplitude+Offset
phase ≥ 0: Offset
Complex-valued signal types (Real part: 0-centered π-wide square wave, Imag leads Real by 90°):
phase in [-π, -π/2): Amplitude + 0j + Offset
phase in [-π/2, 0): Amplitude + 1j·Amplitude + Offset
phase in [ 0, +π/2): 0 + 1j·Amplitude + Offset
phase in [+π/2, +π): 0 + 0j + Offset
Triangle (Phase wraps in [–π,+π], increasing by Frequency/Sample Rate every sample)
Real-valued signal types:
Phase in [-π, 0): Linear ramp from -Amplitude to +Amplitude (both + Offset)
Phase in [0, +π): Linear ramp from +Amplitude to -Amplitude (both + Offset)
Complex-valued signal types (Real part: triangle wave, rising in [-π,0), falling [0,+π), Imag leads Real by 90°):
phase in [-π, -π/2): TODO
phase in [-π/2, 0): TODO
phase in [ 0, +π/2): TODO
phase in [+π/2, +π): TODO
Sawtooth (Phase wraps in [–π,+π], increasing by Frequency/Sample Rate every sample)
Real-valued signal types (Rises from -π to +π, then jumps back to -π):
Amplitude·phase / (2π) + Amplitude/2 + Offset
Complex-valued signal types (TODO)

For selection with a variable, the following values should be used
Constant: analog.GR_CONST_WAVE
Sine: analog.GR_SIN_WAVE
Cosine: analog.GR_COS_WAVE
Square: analog.GR_SQR_WAVE
Triangle: analog.GR_TRI_WAVE
Sawtooth: analog.GR_SAW_WAVE

Message Ports

The 'cmd' message port accepts message pairs.
  • 'freq' . float value
  • 'ampl' . float value
  • 'phase' . float value
  • 'offset' . float value
For GNU Radio 3.8, the messages dont work correctly with pairs, but they do work fine with a dictionary. This issue is explained here.
The amplitude of the signal source can be changed to 0.5 by adding the following PMT to the message strobe block.
 pmt.dict_add(pmt.make_dict(), pmt.intern("ampl"), pmt.from_double(0.5))
The above command creates a dictionary and adds a pmt pair of ("ampl", 0.5) to the dictionary.
The value of frequency in the signal source can be changed by connecting a message strobe. The Message PMT parameter can be set to pmt.from_float(new_freq). In this way, the frequency of the signal source will be changed to new_freq value after the specified period in the message strobe.
The 'freq' message port has been deprecated in 3.9 in favor of the 'cmd' message port.

Example Flowgraph

This flowgraph is for version 3.9+.


Example Output

Types of Waveforms:

Cosine (complex):










Source Files

C++ files
Header files
Public header files
Block definition