Dealing with spikes

 External (or internal) interference (RFI) is a common occurrence with the longer wavelengths in use at the JCMT; that is, particularly in spectra taken with receiver A2. Usually this is offset from the centre of the band and is of no major concern. It seems to be worse for position-switching and may disappear entirely in the azimuth beamswitched mode. Sometimes, however it can be a real nuisance. An example is given in Figure .

 

Such interference spikes may be very effectively removed by applying Hanning smoothing to the spectrum:

$\gt\!\gt$ hann

The result is shown in Figure . A multitude of weak line features, as expected, are now revealed. The spike itself may be removed by using the spike-removal command:

$\gt\!\gt$ rem-spike