Frequency switching with 3 receivers possible

In Newsletter No. 19 (January 1995) we reported on the availability of the frequency switching observing mode at the 30m telescope. The article described several limitations, one of which has been overcome now.

Until recently the software did not allow the simultaneous use of more than 2 receivers for frequency switching. This has been changed, and 3 receivers can be used simultaneously. Several observers already used the 3 mm, 1.3 mm G1 and 2 mm receivers in parallel and in frequency switching mode with good results. The 1.3 mm G2 receiver so far has not been used for frequency switching. However, the observer should be aware of a possible problem with the 3 receiver configuration: baselines may be worse than when using only the 3 mm or/and 1.3 mm 230G1 receivers. This is due to the different optics used for three receivers. An additional polarization grid in the optical path may produce poorer baselines.

We would like to remind the potential users of frequency switching of some parameters:

• Maximum usable frequency throw (in velocity units): 45 km/sec
• Usable backends: autocorrelator, 100 kHz filterbank
• Default switching rate: 1.5 sec per phase (shorter times possible for the 100 kHz filterbank alone)
• Efficiency (time on source/total time spent): > 90%