Remote Spectrum Monitor : Programming with SCPI : Spectrum Trace Data Format
 
Spectrum Trace Data Format
Trace data uses SCPI standard (IEEE 488.2) block data format. The data format is '#AXD', where D is a comma separated list of amplitudes (in ASCII), X is one or more ASCII digits specifying the number of bytes in D, and A is a single ASCII digit specifying the number of digits in X.
Trace data only contains amplitude. The frequency information for each point is
Frequency = [start_frequency + (span/(display_points-1))*N
N = 0, 1, … display_points