  The Tianlai Cylinder Pathfinder is a radio interferometer array designed to
test techniques for 21 cm intensity mapping in the post-reionization Universe,
with the ultimate aim of mapping the large scale structure and measuring
cosmological parameters such as the dark energy equation of state. Each of its
three parallel cylinder reflectors is oriented in the north-south direction,
and the array has a large field of view. As the Earth rotates, the northern sky
is observed by drift scanning. The array is located in Hongliuxia, a
radio-quiet site in Xinjiang, and saw its first light in September 2016. In
this first data analysis paper for the Tianlai cylinder array, we discuss the
sub-system qualification tests, and present basic system performance obtained
from preliminary analysis of the commissioning observations during 2016-2018.
We show typical interferometric visibility data, from which we derive the
actual beam profile in the east-west direction and the frequency band-pass
response. We describe also the calibration process to determine the complex
gains for the array elements, either using bright astronomical point sources,
or an artificial on site calibrator source, and discuss the instrument response
stability, crucial for transit interferometry. Based on this analysis, we find
a system temperature of about 90 K, and we also estimate the sensitivity of the
array.
