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General Signal Viewing > DPX Spectrum DPX Primer
How DPX Works
This section explains how DPX spectrum displays are created. The input RF signal is conditioned and
down-converted as usual for a spectrum analyzer, then digitized. The digitized data is sent through an
FPGA that computes very fast spectral transforms, and the resulting frequency-domain waveforms are
rasterized to create the bitmaps.
The DPX bitmap that you see on screen is composed of pixels representing x, y, and z values for frequency,
amplitude, and hit count (instruments with Option 200 provide Density as the z-axis value in place of hit
count). A multi-stage process, shown in Figures 4a - 4d, creates this bitmap, starting with analog-to-digital
conversion of the input signal.
Simpli fi ed Flow of Multi-stage Processing from RF Input Through to Spectrum Processing:
Figure 4a. RF signals are downconverted and sampled into a continuous data stream.
Figure 4b. Samples are segmented into data records for FFT processing based on the selected resolution bandwidth.
Figure 4c. Data records are processed in the DPX transform engine
Figure 4d. Overlapping the FFTs shortens the minimum event duration required for 100% probability of intercept.
Collecting spectral data.
Sampling and digitization is continuous. The digitized data stream is chopped
into data records whose length is based on the desired resolution bandwidth (RBW). An additional
requirement is placed on FFT length by the desired number of points in a trace (Option 200 only). Table 1
shows this relationship and the FFT length is reported in the display if desired. Then the DPX transform
engine performs a discrete Fourier transform on each record, continually producing spectral waveforms.
RF signals are downconverted and sampled into a continuous data stream.
Samples are segmented into data records for FFT processing based on the selected resolution
bandwidth.
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RSA6100A Series Real-Time Spectrum Analyzers Help