Heterodyne Integration Time Calculator

A web based version of this software is available here. Please contact Remo Tilanus if you have any problems with this software.

N.B. The version available prior to 4/12/01 (version 0.93 or earlier) didn't work out raster mapping correctly (the online version was correct though). RRP

Instructions for Use

The web-based interface is shown below.

Each panel will be described in more detail next. Note that as a general rule the estimated integration time is update whenever you move the mouse away from whichever entry box you have just altered (ie. it is not necessary to press return).

	Using this panel, select the receiver you wish to use. This will automatically update the box showing your desired frequency to the centre of the frequency band for that receiver. Alternatively you can simply type the frequency you wish to observe at directly into the frequency box and the correct receiver will be selected (or a warning message shown if you have selected a frequency that no receiver can tune to). Based on the frequency you entered the receiver temperature (Trx) will be calculated as will the atmospheric opacity and hence the expected system temperature. The value for Trx is taken from a table in the file receiver.info, the first line of which shows the version number, you should always ensure you have the latest version which will contain the latest information on the receiver temperatures which change as we upgrade mixers.
	Using this panel you specify the weather conditions you wish to calculate your observing time in. These categories correspond to the weather bands that you specify on your PATT application form. HITEC contains a model of the atmospheric opacity at all frequencies for which the JCMT has receivers for each of these weatherbands (at Tau(225GHz)=0.5, 0.65, 0.1, 0.16, 0.2). Using this and the frequency you give for the observations it calculates your estimated Tsys value.
	Enter the zenith angle (0 for zenith, 90 for horizon) to include the extra thickness of the atmosphere at lower elevations. You also need to decide what setting on the DAS you wish to use. This can either be done from the pulldown menu or by entering directly the frequency resolution, either as a velocity or a frequency (this would be useful if you are planning to bin your data).
	Using this panel you set up the type of observations you wish to make. Postion switching will spend approximately 50% of the time on an offsource reference position but will generally produce flat baselines. Frequency switch is much more efficient, spending close to 100% of the time on source but will produce wavy baselines that will not be suitable when wide lines are being observed. For producing maps, raster mapping is often the most efficient method with only one offsource reference taken per scan line. If you select this option you need to enter the size of your map (since the integration time will depend on the number of points per row that you select). Some of our receivers have 2 mixers in them (presently B & W) enabling the integration time to be halved although note that it is not possible to use both for all DAS modes, a warning will be shown if you try an illegal combination. Similarly some receivers feature sideband rejection enabling the selection of either Single Side Band (SSB) or Double Side Band (DSB) mode. Trx is higher for SSB but Tsys is colder due to the termination load being colder than the sky. Again a warnign will be issued if you select this for a receiver that cannot reject one side band.
	You can select to enter either a desired 1 sigma rms noise level, in which case the integration time will be calculated, or an integration time can be entered in which case the 1 sigma rms noise level will be calculated. The calculated value updates automatically everytime you change an entry elsewhere on the interface. When a final selection has been made the 'complete answer' button pops up a box giving details of the estimated overheads.