7.1 ON-OFF Techniques

In order to reduce as  much as possible the atmospheric contribution during an observation, it is possible to apply some techniques based on at least a couple of exposures, one on source and one on an adjacent area ("OFF source" reference position), sufficiently free from emission.

At high frequencies short-scale and strong atmospheric fluctuations affect the observation, hence the need of quick antenna shifts between the two positions (which have to be reasonably next to each other) or the usage of other techniques which do not involve the movement of the entire structure, such as On-The-Fly (OTF) scans.

The Noto antenna offers the following ON-OFF technique:

The antenna shifts between two different positions. The time needed to slew to a distance of a few beamsizes is nearly 5 seconds at all frequencies.
The employed algorithm is of the type ON-OFF-ON-OFF.

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