Simple Equations For Frequency Setup

(See examples below)

This page explains how to choose and set up the correlator and downconverter parameters for different correlator bands using the command. See the figure below for more information. There is also a useful on-line tool that will calculate parameters for different setups.

	configCorr(bw, freq, sb, band)

where

	bw:	bandwidth selection for the bandwidth in MHz. One of BW500, BW62, BW31, BW8, BW2
	freq:	2nd LO frequency in GHz
	sb:	2nd downconversion sideband (USB or LSB)
	band:	band number, starting at one

The phase switching CARMA uses allows us to recover both sidebands of the first LO, LO1, from the sky. These are

	fskyUSB = fLO1 + fIF

	fskyLSB = fLO1 - fIF

	sb = -1   for LSB
	sb = +1   for USB

	fskyUSB = fLO1 + (fLO2 + sb x 0.75 GHz)
	fskyLSB = fLO1 - (fLO2 + sb x 0.75 GHz)

	fskyUSB = fLO1 + (fLO2 - 0.75 GHz)
	fskyLSB = fLO1 - (fLO2 - 0.75 GHz)

	fskyUSB = fLO1 + 2 GHz
	fskyLSB = fLO1 - 2 GHz

The nominal IF range is 1.00 to 4.50 GHz, with different telescopes having better performance over different IF frequency ranges. The 6-m antennas have an IF that covers 1.1 to 2.4 GHz. The 10-m antennas operate over the range from 1.0 to 4.5 GHz, although performance is much better in the 2.5 to 3.5 GHz range.

Clicking on the diagram will bring up a PDF version.

Examples And Recommended Configurations

These examples all allow LO2 to default to LSB.

1.  Continuum (baselines, radio pointing, continuum observations, etc.)

Put the first LO at 95 GHz using

    fLO = 95.00
    freq(fLO, USB, 0.00, 'none')

Place bands 1 and 2 to cover the BIMA IF, and band 3 at higher IF for OVRO antennas

    configband(1, BW500, fLO + 1.65)
    configband(2, BW500, fLO + 2.15)
    configband(3, BW500, fLO + 3.2)

or equivalently put the first LO at 95 GHz using

    fcenter = 97.15
    freq(fcenter, USB, 2.15, 'none')

Place bands 1 and 2 to cover BIMA IF, and band 3 at higher IF for OVRO antennas

    configband(1, BW500, fcenter - 0.50)
    configband(2, BW500, fcenter)
    configband(3, BW500, fcenter + 1.05)

2.  Line observations (fixed correlator settings)

For line observations with one or two narrow narrow bands and one 500-MHz band on source, and where the phase calibration source is strong enough to be calibrated without changing correlator modes between source and calibrator, i.e. on the one 500-MHz band. This setup applies to 2, 31, 61 MHz bandwidths as well as the 8 MHz bandwidth in this example.

Put the most important line at 2.15 GHz in the IF using

    fline = linefreq('CO')
    freq(fline, USB, 2.15, 'sourcename')

a) Continuum band overlapping the line(s) at 2.15 GHz IF

e.g., for maximum continuum sensitivity

     configband(1, BW500, fline)        !to give a continuum band 

centered on the line, on a standard LO2 frequency

     configband(2, BW8, fline)          !first 8-MHz line band
     configband(3, BW8, fline - 0.008)  !second 8-MHz line band

below the line. Or, choose another offset for a different line.

b) Continuum band not overlapping the line(s), to avoid contamination

     configband(1, BW500, fline - 0.5)  !to give a continuum band

centered below the line but still on a standard LO2 frequency

     configband(2, BW8, fline)          !first 8-MHz line band
     configband(3, BW8, fline - 0.008)  !second 8-MHz line band

below the line. Or, choose another offset for a different line.

These examples preserve the 500 MHz bands at the "standard" positions of 1.65, 2.15, 3.2 GHz.

3. Line observations with variable correlator configuration

For line observations where the correlator configuration must be changed between the source and calibrator to ensure adequate S/N on the phase calibrator and appropriate spectral line modes for the source:

On the source, set the first and second LO frequencies to cover the lines of interest, with reference to the explanations above these examples.

     fLO = x
     freq(fLO, USB, 0.00, 'none')

     configband(1, BW8, fband1))
     configband(2, BW8, fband2)
     configband(3, BW8, fband3)

On the phase calibrator retain the same fLO and use the setup:

     configband(1, BW500, fLO + 1.65)
     configband(2, BW500, fLO + 2.15)
     configband(3, BW500, fLO + 3.2)

On a strong bandpass calibrator (usually a planet), observe each of the above modes, and also hybrid modes sufficient that each narrow-band tuning is observed simultaneously with a wideband tuning, at the same frequencies at which they were used on the source/calibrator observations, e.g.,

     configband(1, BW8, fband1)
     configband(2, BW500, fLO + 2.15)
     configband(3, BW8, fband3)

then

     configband(1, BW500, fLO + 1.65)
     configband(2, BW8, fband2)
     configband(3, BW8, fband3)

Note that this mode is somewhat complex and the proposer should consult with CARMA experts for further information.

From Stuart Vogel:

Regarding the "hybrid" mode calibrations mentioned at the end, 2 minutes
on a 5 Jy source suffices, except perhaps for 2 MHz, which might need 
4 minutes (at CO the numbers would increase a bit).  For the channel to 
channel passband calibrations, if needed, obviously more time would be 
important; note that the hybrid band observations do not need channel to 
channel calibration, at least not at high S/N; if the all wide-band and 
all-spectral-line modes don't need channel to channel calibration, then 
their integration times can be similarly short on a 5 Jy source, and in
fact the all spectral line mode observation of the bandpass/offset 
calibrator is not essential, except it is useful as
a sanity check, ie that the phases close.

(Note that in each case the 500-MHz band is one of the bands available on all antennas, i.e. below the BIMA antenna cutoff of 2.4 GHz).