Pulsed Signal Sampling

In some applications, microwave generators are modulated by fast rectangular pulses with durations in some cases as short as tens of microseconds. This type of signal is referred to as Pulsed. The Homer is capable of processing pulsed signals with pulse durations down to 50 microseconds. The Pulsed sampling mode is intended for these types of signal.

The parameters governing Pulsed sampling are shown in the table below. Refer to Fig. 25 for the symbols in parentheses in the left column. The middle column shows the settings via the Homer Sampling Setup window of HomSoft, plus an alternative (mostly a toolbar button) if one exists. The right-hand column shows examples of Hom.cfg settings for Homer autonomous operation.

Parameter

Setting via HomSoft

Example Setting in Hom.cfg

Sampling time (Ts)

Sampling Time edit box. Valid range 10 ms to 10 s.

Puls_Tsampl_Us=2000
(Ts = 2 ms)

Sample count (Ns)

Sample Count edit box. Valid range 21 to 4095.

Puls_Nsampl=201
(Ns = 201)

Timeout (Tmax)

Max Period edit box. Valid range 1 ms to 10 s.

Puls_Tmax_ms=100
(Tmax = 100 ms)

Sampling rate (fs)

Computed internally by Homer.

n. a.
(fs = 100 kHz)

Acceptance level
(Lacc)

Accept Level edit box. Valid range 0 to 100% of pulse height. Recommended setting 5 to 20%.

Puls_Acc_Lvl=10
(Lacc = 10%)

Frequency counting time (Tc)

Count Time edit box or  Tc  Standard toolbar button (Fig. 15). Valid range 16 ms to 1 s.

Puls_Tcnt_Us=50
(Tc = 1 ms; will be truncated to n × 16 ms = 48 ms)

Triggering level
(Ltrg)

Trig Level edit box or Signal toolbar button. Valid range 1 to 99% of the ripple peak-to-peak value.

TrgLevel=50
(Ltrg = 50%)

Free Run

Free Run checkbox or / Signal toolbar button. Normal setting is unchecked ().

TrgMethod=1
(Free Run = FALSE)

Notes:

  • Sampling time has precedence over sample count. If the desired sampling time and the sample count would lead to a sampling rate higher than 200 kHz, the sampling rate will be set to 200 kHz and the sampling count will be reduced to maintain the desired sampling time.

  • Timeout (Tmax) is the maximum wait time for a triggering event to occur, i.e., the maximal expected pulse repetition period. If no triggering event occurs during this timeout interval, measurement will start automatically on Tmax expiration. Please also refer to the topic Triggering.

  • Enabling Free Run temporarily instead of triggering may be useful if one wishes to inspect a signal waveform that will not trigger.

  • Frequency counting time Tc should be shorter than a single pulse duration.

Pulsed signals are thus sampled over a user-defined sampling time Ts. After being collected, the samples are processed individually to yield particular results for each sample (reflection coefficient, incident power, reflected power). These particular results are then averaged to yield the final results of interest. The rules for averaging are as follows:

  • Incident and reflected powers are, unlike in Rectified mode, averaged only over the accepted samples. This yields the mean power in pulse. For rectangular pulses, this is equal to the peak power.

  • Reflection coefficient is averaged only over the accepted samples. The accepted samples are those with the incident power exceeding the set Accept Level (Lacc).

In addition to the averaged results, the results corresponding to each particular sample can also be viewed. To learn more about this, go to the topic Displaying Individual Samples.

The Homer must be informed of the type of signal waveform it will be confronted with (in this case Pulsed). Following this, the corresponding sampling parameters can be modified.

To select Pulsed mode of signal sampling:

Open the Homer Sampling Setup window and click the Pulsed tab. Alternatively, click the Signal toolbar button (Fig. 15).

To set sampling parameters:

In the Homer Sampling Setup window:

  • Edit Sampling Time to set the sampling time Ts in appropriate units.

  • Edit Sample Count to set the number of samples Ns to be collected during the sampling time.

  • Edit Max Period to set the maximal expected pulse repetition period Tmax.

  • Edit Accept Level to set the acceptance level Lacc in % of pulse height.

  • Edit Count Time or click the  Tc  Standard toolbar button (Fig. 15) to set the signal frequency counting time Tc in microseconds.

  • Edit Trig Level or click to set the trigger level Ltrg in % of ripple peak-to-peak value.

  • Check Free Run or click the / button to enable/disable sampling without triggering.

  • Check Send Samples or press the sbSamples button to display individual samples. To learn more, go to Displaying Individual Samples.

  • Click the  Refresh  button to check/correct the entered values and compute the derived parameters (Sampling Rate, Sampling Step).

  • Click the  Apply  button to accept the changes, or click  Cancel  to ignore all changes. (The  Apply  button also automatically performs the Refresh action.)