Frequency Selection

Frequency selection expression consists of two specifications separated by colon (':') in the form:

      SPWSPEC[:CHANSPEC]

where SPW is the spectral window specification and CHANSPEC is the optional frequency specification for selection within the selected spectral windows. When channel specification is omitted, all channels of the selected SPW are selected.

SPWSPEC and CHANSPEC allow use of semi-colon separated lists. As a result, list of SPWSPEC can be given in two ways: (1) a semi-colon separated list, (2) coma separated list. This allows simple selections to remain simple and more complex selections consistent with the syntax for CHANSPEC list.

Spectral Window Specification Syntax

Spectral windows (SPW) specification can be a single ID or a list of spectral window integer IDs, a spectral window name (as a literal string (for exact match)/regular expression/pattern) or a reference frequency value (value with a unit). A single frequency specification is used for exact match with the REF_FREQUENCY column of the SPECTRAL_WINDOW sub-table. A range of frequencies are used to select all SPWs which are within the given range. The allowed units are Hz, KHz, MHz, GHz or THz.

SPWs can also be selected via a boolean expression for integer IDs.

• "$>$ ID" will select all SPWs with ID greater than the specified value.
• "$<$ ID" will select all SPWs with ID lesser than the specified value.
• "$>$ FREQ" will select all SPWs, the reference frequencies of which are greater than the given frequency converted to Hz.
• "$<$ FREQ" will select all SPWs, the reference frequencies of which are greater than the given frequency converted to Hz.

E.g.

• spw=1,2,3 selects spectral window IDs 1,2 and 3
• spw=1;2;3 same as above. This style can be used along with CHANSPEC
• spw=1$\sim$ 3 same as above
• spw=327MHz selects spectral window with a reference frequency equal to 327.0 MHz
• spw=327$\sim$ 610MHz selects all spectral windows with reference frequencies in the range [327.0, 610.0] MHz.
• spw=1421MHz, 1422MHz, 1423MHz selects SPWs with reference frequency 1421.0, 1422.0 and 1423.0 MHz.
• spw=1421MHz; 1422MHz; 1423MHz same as above. This style can be used along with CHANSPEC.
• spw=$>$ 327MHz selects all spectral windows with reference frequency greater than 327.0 MHz
• spw=$<$ 327MHz selects all spectral windows with reference frequency less than 327.0 MHz

Channel Selection Syntax

Channel specification¹ (referred to as CHANSPEC in the following description) is a START,STOP,STEP tuple corresponding to the first frequency channel, the last frequency channel and the step size to increment from the first to the last channel. The START and STOP part of the tuple can be range specification for the range [START, STOP] followed by an optional STEP size.

START and STOP part of the tuple can be specified as a single integer or physical quantity or as a range of integers or physical quantities. A single integer is treated as a channel index and the tuple corresponds to [ID,ID,1]. A single physical quantity is matched with the exact frequency value of the channels and tuple of matched channel index is constructed as [ID,ID,1]. A range of integers given as N0$\sim$ N1 is used to construct a tuple [N0,N1,1]. Similarly for a range of physical quantities.

If a START,STOP part of the tuple specification is followed by "^STEP", the STEP is used as the third value of the tuple. STEP specification is a single integer or physical quantity. E.g. 0$\sim$ 10^2 is converted to a START,STOP,STEP tuple [0,10,2].

A channel selection expression is a semi-colon separated list of channel specifications. E.g.

• chan=1;2;3 selects channels 1,2 and 3.
• chan=1$\sim$ 3 selects channels 1,2 and 3.
• chan=0$\sim$ 10^2 selects channels in the range [0,10] with a step size of 2
• chan=1421MHz selects a frequency channel corresponding to the frequency 1421.0 MHz
• chan=1421$\sim$ 1500MHz selects all channels in the range [1412.0, 1500.0] MHz
• chan=1421$\sim$ 1500MHz^10KHz selects all channels in the range [1421.0, 1500.0] MHz in steps of 10 KHz.
• chan=1421$\sim$ 1500MHz^10KHz ; 0$\sim$ 10^2 ; 20 ; 30; 40 selects all channels in the range [1421.0, 1500.0] MHz in steps of 10KHz, all channels with indexes in the range [0,10] in steps of 2 channels and channels 10, 20 and 30.

Frequency Selection Syntax

The specifications for SPW and channels can be combined to form a fully qualified frequency selection expression in the form SPWSPEC[:CHANSPEC] (square brackets indicate that :CHANSPEC is optional). A frequency selection expression is a comma-separated list of SPWSPEC[:CHANSPEC] specifications. Channel selections apply to all SPWs selected by the SPWSPEC on the left of ':'. E.g.

• freq=LBAND:1421$\sim$ 1500MHz^10KHz , 327MHz:300$\sim$ 400MHz, 0$\sim$ 4:0$\sim$ 10^2 , 5:20;30;40

  selects

  • all channels corresponding to channels in the range [1421.0, 1500.0] MHz for the SPW named "LBAND", and
  • all channels corresponding to the range [300.0, 400.0]MHz for the SPW with a reference frequency of 327.0 MHz, and
  • Channels in the range [0,10] in steps of 2 for all SPWs with IDs in the range [0,4], and
  • Channels 20, 30 and 40 for SPW 5

• freq=1421Mhz;1422Mhz;1423Mhz : 0;1;2;10$\sim$ 20;30$\sim$ 100$\sim$ 10 ,0$\sim$ 3:10$\sim$ 30

  selects

  • Channels 0, 1, 2 for SPWs with reference frequency of 1421.0, 1422.0 and 1423.0 MHz.
  • Channels 10 to 20 in step of 1 channel for SPWs with reference frequency of 1421.0, 1422.0 and 1423.0 MHz.
  • Channels 30 to 100 in steps of 10 channel for SPWs with reference frequency of 1421.0, 1422.0 and 1423.0 MHz.
  • Channels 10 to 30 in step of 1 channel for SPW IDs 0 to 3 in step of 1.

Notes

1. For channel specifications of the type N1$\sim$ N2:c0;c1;c2;c3MHz the list of channel selection is applied to all SPWs in the range [N0, N1]. c3 is converted from physical units to channel index by using the channel width from SPW N1. Is it better to use the min. chan. among the selected SPWs?

2. If channel range is out of bounds, it will be brought within bounds per SPW. If the lower limit of a range is greater than the available outer limit, exception is generated. If the lower limit is less than zero, it is set to zero. If upper limit is greater than the available outer limit, it is set to the available outer limit.

   If a single channel specification is greater than the available outer limit, an exception is thrown. If it is less than zero, it is set to zero.

3. For ranges of physical values, it is assumed that the spectral window sub-table's CHAN_FREQ column has ordered list of channel frequencies.