Tektronix SPECMON3 Manual page 174

RF Measurements
Parameter
Average
Frequency-domain
Time-domain
Number
Correct for Noise Floor
Power Reference
Channel Filter
Filter Parameter
Chip Rate
xxx
Correct for Noise Floor
When this setting is enabled, the instrument applies a correction to the ACPR or MCPR measurement to
reduce the effect of instrument noise on the results. It generates this correction by taking a preliminary
acquisition to measure the instrument noise floor. Once this is done, the measurement proceeds, applying
the correction to each result. When any relevant settings (reference level, attenuator, frequency, or span)
are changed, the instrument performs a new noise measurement and correction.
The noise correction signal is created by switching off the input to the RTSA and performing acquisitions
of the instrument internal noise. 100 acquisitions are averaged to create the noise reference signal. A single
value of noise is measured for each channel defined by the measurement. The noise reference from each
channel is subtracted from the incoming signal power for each channel to create the corrected result. All
calculations are performed in Watts, and then converted to the desired units.
The amount of noise correction is limited to 12 dB to avoid the possibility of a negative power
measurement. This is a rare condition that could occur if the subtraction of the reference power from the
channel power results in a negative value (or 'infinite' dBm).
162
Measurement Params for ACPR and MCPR Displays
Description
Enables/disables measurement averaging. Averaging can be enabled in either the
Frequency Domain or Time Domain.
This setting takes the average linear value of the traces (so that rms values are
preserved). The number of averages is user-defined. Frequency domain averaging
is available in spans larger (or smaller) than the maximum real time bandwidth.
This is the mode to use unless you need to extract maximum dynamic range from
an ACPR measurement.
This setting takes the average linear value of the traces. It is useful if you need to
extract maximum dynamic range from an ACPR measurement. The number of traces
is user defined. But, the signals must be triggered and repeating. That is, the signal
needs to be exactly the same for each acquisition. When this condition is met, each
waveform contains the same signal, but the random noise changes from acquisition
to acquisition and the average value of the random noise is lowered, while the signal
value remains constant. Time domain averaging is not available in spans wider
than the maximum real-time bandwidth.
Specifies the number of acquisitions to be averaged when Averaging is set to
Frequency Domain. Specifies the number of successive capture records that are
averaged when Averaging is set to Time Domain.
Enables/disables the Noise Floor Correction function.
Specifies power against which the results are compared. Choices available are each
of the existing main channels and "Total (active channels".
Only present when MCPR is the selected display.
Specify the channel filter used. Select between None (default) and Root-raised
Cosine.
Value entry box for the Root-raised Cosine filter Adjacent Channel Filter.
Present only when the Channel Filter is set to Root-raised Cosine.
Value entry box for the Root-raised Cosine chip rate.
Present only when the Channel Filter is set to Root-raised Cosine.
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