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Frequency cycling observations
In frequency cycling, the tuning frequency is regularly cycled between
predefined values inside the same receiver RF band. This
first imply that the on-source observing time must be split between the
different tuning of the frequency cycling. To do this, the user will have
to give the percentage of the time required per tuning. The sum of the
percentage will have to be equal to 100%. By default, PMS will divide
equally the on-source time between the tunings, and the user will have
the possibility to modify this time repartition.
Frequency cycling also has two consequences on the observational efficiency.
- The time to setup the tunings is increased with respect to
standard observations by
, where
is
typically XXX minutes.
- After the setup phase, each cycle observed at a given
frequency must be surrounded by gain calibration observations at
the same frequency. This means that the observing efficiency is
decreased: in practice this is like doubling the number of
calibrators, since each calibrator will have to be observed at the
2 frequencies (the frequencies of the previous and of the next
cycle, whatever the number of cycles).
To take this into account, we first define the overhead factor as
 |
(38) |
The overheads are now split into generic overheads, independent of the
number of gain calibrators, and the calibration overheads that is
directly proportional to the number of observed gain calibrators. This
gives
 |
(39) |
We will use
and
,
or 2 for detection or imaging,
respectively, and
in frequency cycling mode, 1
otherwise.
When frequency cycling is combined with dual band observations, it is
emphasized that both receiver bands are affected by the efficiency loss
of the frequency cycling even though one of the two bands could not
require frequency cycling at all.
Subsections
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Gildas manager
2024-09-01