Sweep Mode

Table of Contents

• Example
• Basics
• Sweep Format
• Min and Max Sweep Arrays

Sweep mode represents the common spectrum analyzer measurement of plotting amplitude over frequency. The API provides a simple interface through spGetSweep for acquiring single sweeps.

Example

For a list of all examples, please see the examples/ folder in the SDK.

 
#include <cstdio>
#include <cstdlib>
#include <vector>
 
#include "sp_api.h"
 
// Configure the device for sweeps and perform a single sweep.
void sp_example_sweep()
{
    int handle = -1;
    SpStatus status = spNoError;
 
    status = spOpenDevice(&handle);
 
    // Check open status
    if (status != spNoError) {
        printf("Unable to open device\n");
        exit(-1);
    }
 
    // Configure the sweep
    spSetRefLevel(handle, -20.0); // -20dBm reference level
    spSetSweepCenterSpan(handle, 2.45e9, 100.0e6); // ISM band
    spSetSweepCoupling(handle, 10.0e3, 10.0e3, 0.001); // 10kHz rbw/vbw, 1ms acquisition
    spSetSweepDetector(handle, spDetectorAverage, spVideoPower); // average power detector
    spSetSweepScale(handle, spScaleLog); // return sweep in dBm
    spSetSweepWindow(handle, spWindowFlatTop);
 
    // Initialize the device for sweep measurement mode
    status = spConfigure(handle, spModeSweeping);
    if (status != spNoError) {
        printf("Unable to configure device\n");
        printf("%s\n", spGetErrorString(status));
        spCloseDevice(handle);
        exit(-1);
    }
 
    // Get the configured sweep parameters as reported by the receiver
    double actualRBW, actualVBW, actualStartFreq, binSize;
    int sweepSize;
    spGetSweepParameters(handle, &actualRBW, &actualVBW, &actualStartFreq, &binSize, &sweepSize);
 
    // Create memory for our sweep
    std::vector<float> sweep(sweepSize);
 
    // Get sweep, ignore the min sweep and the sweep time
    status = spGetSweep(handle, nullptr, sweep.data(), nullptr);
    if (status != spNoError) {
        printf("Sweep status: %s\n", spGetErrorString(status));
    }
 
    // Done with the device
    spCloseDevice(handle);
}

Basics

Only 1 sweep configuration can be active at a time.

Changing a sweep setting requires reconfiguring the device with a new sweep configuration.

All sweeps must be finished to change sweep configuration.

The maximum sweep speed that can be achieved is ~200GHz/s. This can only be achieved with wide spans and large RBWs.

Only linear spaced sweeps can be performed.

Sweep Format

A sweep is returned from the API as a 1-dimensional array of measurement values. Each element in the array corresponds to a specific frequency. The frequency of any given element can be calculated as

Frequency of N'th element in sweep = StartFreq + N * BinSize

where StartFreq and BinSize are reported in the spGetSweepParameters function.

The measurement values can be returned in dBm or mV units.

Min and Max Sweep Arrays

All sweep functions in the API return 2 separate sweep arrays. The parameters are typically named sweepMin and sweepMax. To understand the purpose of these arrays, it is important to understand their relation to the analyzer’s detector setting. Traditionally, spectrum analyzers offer several detector settings, the most common being peak-, peak+, and average. The API reduces this to either minmax or average. When the detector is set to minmax, the sweepMin array will contain the sweep as if a peak- detector is running, and the sweepMax array will contain the sweep of a peak+ detector. When average detector is enabled, sweepMin and sweepMax will be identical arrays and will be the result of an average detector.

If you are not interested in one of the sweeps, you can pass a NULL pointer for this parameter and it will be ignored.

Most users will be interested in the sweepMax array as it will provide you either the peak+ and average detector results depending on detector setting. In this case, pass NULL for the sweepMin parameter.