Beamformer Coherency Commissioning Tests in 1K-mode at L-band
Similar to an earlier commissioning report (M2600-0000-010) on the coherency of the MeerKAT Tied-Array Beam (TAB) in the 4096 frequency channel (4K) mode, this report investigates the level of coherency of the TAB in the 1024 frequency channel (1K) mode at L-band frequencies (856 MHz to 1712 MHz). The 1K-mode is designed specifically for high precision pulsar timing work, exchanging frequency resolution for higher timing resolution, and is the preferred mode for most Meertime1 pulsar
... 1 pulsar observations. In the 1K folded mode used here, the Pulsar Timing User Supplied Equipment (PTUSE) provides 8 second folded profiles, with 1024 phase bins per profile, similar to the 4K folded mode. The data quality of the TAB is monitored while observing a well-known pulsar and changing the number of antennas used to form the TAB. The signal-to-noise-ratio (S/N) of the pulsar observation is expected to increase linearly with an increasing number of antennas. Perfect antenna addition would produce a coherency value (α) of 1.0. The primary target used for these tests is PSR J1056−6258, as per the 4K report (M2600-0000-010), along with a couple of observations using PSR J1644−4559. The TAB coherency specification is described in R.C.SP.23 CBF TA beamforming efficiency as follows: "The Correlator Beamformer (CBF), when requested to produce one or more TA beams, shall maintain, with an efficiency factor of >= 0.95, constant S/N per TA produced." We find that this specification is met by achieving a mean coherency factor of hαi = 0.99±0.01 and a minimum α value using PSR J1056−6258 of 0.95±0.03.