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A Spectral Window summary table is visible above the spectral window specification tabs. Apart from a few fields the table also shows the data rates and the sky frequency that can be expected for each spectral window.
Figure 6.19:
The
Spectral Window forms
to provide the Spectral Windows specifications.
|
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SpectralWindow Name
: A locally unique name for this spectral window, Automatically set.
-
Center Offset Frequency
: The center frequency of the spectral window, between 2000 and 4000 MHz. This value is an offset into the 2GHz bandwidth of the baseband. Can only take discrete values, determined by the step size of the band, i.e. 2GHz/8192 = 244.141 kHz.
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Center Freq(Rest) LSB/USB
: The center rest frequency for the LSB and USB.
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Center Freq(Sky LSB/USB
: The center sky frequency for the LSB and USB.
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Use LSB - Use USB
: Check when using LSB, USB, DSB or NOSB. Note that if this spectral window is LSB, then its frequency (or channel) order is reversed from the sky frequency, i.e., lowest sky frequency is highest baseband frequency. The sideBand mode should be common to all spectral windows in a baseband for SSB receivers.
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Nominal BW # Channels
: The nominal bandwidth and number of channels of the spectral window.
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Effective BW # Channels
: The effective bandwidth of the spectral window and the effective number of channels in the spectral window. The effective number of channels is same as the nominal one for ACA correlator, and by 1/16 less than the nominal one for BL correlator.
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Resolution
: The spectral resolution.
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CorrConfigMode/Filtermode
: Correlator configuration internal mode number and filter type.
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Polarization Products
: Options: XX, YY (single pol'n) or XX,YY, (dual pol'n) or XX, YY, XY, YX (full pol'n). The ACA correlator always outputs all 4 polarization products. The ACA correlator will share the setup if it is common to all spectral windows in a baseband. For the ACA correlator, the polarization products can not be changed by the spectral windows.
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Averaging Factor
: Specifies the number of spectral channels to average together for each subband. This factor is the number of adjacent channels to average together and must be a power of 2, e.g., 1, 2, 4, 8, etc. The spectral averaging factor can be used to reduce the amount of spectral data sent to the Archive.
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Window Smoothing Function
: An enumerated value representing the data smoothing function to use. One of: UNIFORM, HANNING, HAMMING, BARTLETT, BLACKMANN, BLACKMANN_HARRIS, WELCH.
The following
BL Only
subpanel applies to the Baseline Correlator Setup only:
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Correlation Bits
: The correlation bits settings for the baseline correlator. Options are: 2x2, 3x3, 4x4. Higher numbers will increase the sensitivity but requires more resources.
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Oversampling
: Nyquist sampling/oversampling. True means do Nyquist oversampling, False means non-oversampling.
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Quantization Correction
: Boolean selection to perform quantization ('VanVleck') correction on the lag data. Normally this is true, but for diagnostic purposes, we may wish to view the uncorrected lags. The ACA correlator does not use this parameter, because the ACA-CDP always does the quantization correction on the spectral results.
On the right side the Spectral Average Region table is visible that can be used to specify the spectral bands that are to be averaged. The user can select up to 10 sets of contiguous channels (a ChannelAverageRegion) which contribute to the channel average result. Note that these parameters are based on effective channels. That is, Start Channel must be a zero based index within the effective range of spectral channels and the number of channels is interpreted based on the spectral resolution (band-width per channel) before any spectral averaging (spectralAveragingFactor) has been applied.
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Start Channel
: Starting (0-based) channel used to calculate the spectral channel average for a given region. This should be an unsigned type.
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Num. Channels
: Number of spectral channels used to calculate the spectral channel average for the region. This should be a positive integer.
Next:
Observing Parameters
Up:
BaseBand Configuration
Previous:
BaseBand Configuration Forms
Contents
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The ALMA OT Team, 2011 May 20