I don’t see the post I made yesterday up here, so here I go again.
As I said before, I decided to get an SM200A and see how that works. The queuing up of sweeps is huge and really this device is much faster.
Right now I’m scanning 100MHz at ~0.3ms, which is great. Theoretically it could go as fast as 0.1ms (1THz/s sweep rate). I expect that a lot of the increase in time is sweeping the LO back to the beginning of the spectrum? I’m not sure.
Either way, I’m pretty happy with the SM200A and it’s performance.
The capture is a bit noisier, which will require me to add some smoothing or similar to my algorithms, but it’s not a huge deal.
Overall, if I could eek out a bit more performance (faster scans), that would be great. Here’s some prototype code I was using to test it below; any thoughts?
Again, great device!
// Configure the receiver sweep functionality
// Things to note for THz sweep speeds
// smSweepSpeedFast must be set
// RBW must equal VBW and be above 30kHz for Nuttall window
sm_api.smSetSweepSpeed(handle, SmSweepSpeed.smSweepSpeedFast);
sm_api.smSetRefLevel(handle, -20.0); // -20dBm reference level
sm_api.smSetSweepCenterSpan(handle, 2.45e9, 1.0e8);sm_api.smSetSweepCoupling(handle, 100.0e3, 100.0e3, 0.001); // 100kHz rbw/vbw
sm_api.smSetSweepDetector(handle, SmDetector.smDetectorAverage, SmVideoUnits.smVideoPower); // min/max power detector
sm_api.smSetSweepScale(handle,SmScale.smScaleLog); // return sweep in dBm
sm_api.smSetSweepWindow(handle,SmWindowType.smWindowNutall);
sm_api.smSetSweepSpurReject(handle,SmBool.smFalse); // No software spur reject in fast sweep
sm_api.smSetPreselector(handle, SmBool.smFalse); // No preselector in fast sweep// Initialize the device for sweep measurement mode
SmStatus status = sm_api.smConfigure(handle,SmMode.smModeSweeping);
double actualRBW = 0, actualVBW = 0, actualStartFreq = 0, binSize = 0;
int sweepLength = 0;
sm_api.smGetSweepParameters(handle, ref actualRBW, ref actualVBW, ref actualStartFreq, ref binSize, ref sweepLength);float[] sweepMax, sweepMin;
sweepMax = new float[sweepLength];
float[][] sweepsMax = new float[1000][];
float[][] sweepsMin = new float[1000][];
for (int i = 0; i < 1000; i++)
{
sweepsMax[i] = new float[sweepLength];
sweepsMin[i] = new float[sweepLength];
}
sweepMin = new float[sweepLength];long[] sweeptimeEpoch = new long[1000];
//the API allows us to queue up to 16 sweeps. They recommend queueing ~4 sweeps
//but we’re pretty narrow sweeps, so let’s try 12 to start…
// Start all sweeps in queue
int sweepsToQueue = 16;
for (int i = 0; i < sweepsToQueue; i++)
{
sm_api.smStartSweep(handle, i);
}
int j = 0;
int queuePos = 0;
while (j < 1000)
{
SmStatus status = sm_api.smFinishSweep(handle, queuePos, null,sweepsMax[j], ref sweeptimeEpoch[j]);// Process/store sweep here
// Sweep in contained in the ‘sweep’ array// Start it back up
sm_api.smStartSweep(handle, queuePos);// Increase and wrap our queue pos
queuePos++;
if (queuePos >= sweepsToQueue)
{
queuePos = 0;
}j++;
}