All the above numeric calculations apply to our current situation.
Naturally, there is work ongoing both to reduce the minimum integration time
and to increase the maximum number of frequency points. We list some
of these efforts below to whet the appetite.
All of these statements are
based on my current understanding of the various projects, and not
necessarily on any actual testing.
- The PCI (Post-correlator integrator) aims to allow integrations
as short as 1/64s for the full correlator. Indeed, it has been
the first stage of
this project that has allowed us to drop the full-correlator minimum
to 0.25s; thus another factor of 16 remains.
Promising tests have recently been conducted at
- Recirculation can increase for experiments that use
MHz (by the factor
the rules that a single baseline/subband/polarization product must
fit onto a single correlator board (thus the maximum )
would still apply. The type of experiment that would benefit most
from recirculation from a practical viewpoint would be narrow-band global
spectral line -- if
MHz, then the factor-of-4
``penalty" incurred in increasing from 8 to 16
(cf. equation 4 or table 1) can be
absorbed by recirculation (
), allowing a global experiment to achieve
the same as an 8-station experiment can currently.
However, should recirculation be used, the minimum integration time
would be increased by a factor of from its nominal value.
- We now operate using so-called ``local" validity. ``Global" validity
would increase the number of possible frequency points (and also the
output size of the data) by a factor of
two . We don't currently use this because it problems ensue
for MkIV-MkIV baselines (i.e., when both stations use a
data-replacement frame-header format) when the a priori delay
is such that portions of both frame headers correlate against each other.
The data in affected time ranges must be flagged
(and this time range increases with ,
resulting in more data loss specifically in those cases you'd most want to
take advantage of the extra factor of 2 -- for more information about
this, see ftp://ftp.jive.eu/outgoing/rmc/dlyrt0.ps.gz).
In the future,
this problem should be avoided with Mark5B recordings, which when
played back should output
a non data-replacement frame-header format. This doubling of the
effective correlator capacity would also increase the maximum
Until the full PCI is on-line, there may also be a corresponding
factor of two penalty in the minimum integration time (because of the
larger data-block size).