Downconverts real passband signal data of a user-specified bandwidth. This node can be used in simulated as well as hardware-equipped applications.
Signal for downconversion in passband form.
The center frequency of the passband, in hertz (Hz). This frequency is downconverted to 0 Hz. Enter the expected carrier frequency of the incoming signal for downconversion.
The bandwidth, in Hz, of the passband signal data. The node ignores this parameter if you set the reset? parameter to FALSE.
Filter parameters.
The ripple in the passband, in dB. The ripple is the ratio of the maximum deviation from the average passband amplitude to the average passband amplitude. The value must be greater than zero.
Default: 0.01
The start of the stopband, Hz.
Default: 0
A Boolean that determines whether to compute the stopband start or use the value that you specify in the stopband start parameter.
TRUE | Computes the stopband start based on the carrier frequency and passband bandwidth parameters. |
FALSE | Uses the value that you specify in the stopband start parameter. |
Default: TRUE
The stopband gain, in dB. The gain is the negative of the minimum attenuation of the stopband with respect to the average amplitude of the passband.
Default: -96
Error conditions that occur before this node runs. The node responds to this input according to standard error behavior.
Default: no error
A Boolean that determines whether to perform software filtration on the downconverted data.
TRUE | The node filters the downconverted waveform parameter using a software FIR filter. |
FALSE | Disables the downconversion filter and generates unfiltered data in the downconverted waveform parameter. |
Default: TRUE
A Boolean that determines whether to use values specified by the initial phase, passband bandwidth, enable filter, passband ripple, and stopband start parameters.
TRUE | The node uses these parameter values at each call. |
FALSE | The node ignores these parameters and continues using values supplied in the previous call. Reusing previous input values is useful when sequential data blocks represent contiguous signal data. |
Default: FALSE
The initial phase, in degrees, of the software local oscillator used in the downconversion process. The node ignores this parameter if you set the reset? parameter to FALSE. Use the initial phase parameter to match the phase of the incoming modulated carrier and the local oscillator(s) of the downconversion process.
The downconverted signal in complex envelope format.
The trigger (start) time of the acquired signal.
Time interval between data points in the acquired signal.
The complex-valued time-domain data array. The real and imaginary parts of this complex data array correspond to the in-phase (I) and quadrature-phase (Q) data, respectively.
The deviation of the passband gain from the nominal gain of 0 dB.
Number of taps in the filter.
Error information. The node produces this output according to standard error behavior.
where
P is the filter order
x[n] is the input signal
y[n] is the output signal
b_{i} are the filter coefficients
The initial state for all samples in an FIR filter is 0. The filter output until the first input sample reaches the middle tap (the first causal sample) is called the transient response, or filter delay. For an FIR filter that has N taps, the delay is (N-1)/2 samples. This relationship is illustrated in the following figure, where a sine wave is filtered by an FIR filter with 50 taps.
In single-shot operations for modulators and demodulators, the filter delay is truncated before the signal is generated because these samples are not valid. Some samples at the end of the block do not appear at the modulator or demodulator output, and hence appear to have been lost.
Installed By: LabVIEW Communications System Design Suite (introduced in 1.0)
Where This Node Can Run:
Desktop OS: Windows
FPGA: Not supported
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