  We present the analysis of 26 nights of V and I time-series observations from
2011 and 2012 of the globular cluster M 30 (NGC 7099). We used our data to
search for variable stars in this cluster and refine the periods of known
variables; we then used our variable star light curves to derive values for the
cluster's parameters. We used difference image analysis to reduce our data to
obtain high-precision light curves of variable stars. We then estimated the
cluster parameters by performing a Fourier decomposition of the light curves of
RR Lyrae stars for which a good period estimate was possible. We also derive an
estimate for the age of the cluster by fitting theoretical isochrones to our
colour-magnitude diagram (CMD). Out of 13 stars previously catalogued as
variables, we find that only 4 are bona fide variables. We detect two new RR
Lyrae variables, and confirm two additional RR Lyrae candidates from the
literature. We also detect four other new variables, including an eclipsing
blue straggler system, and an SX Phoenicis star. This amounts to a total number
of confirmed variable stars in M 30 of 12. We perform Fourier decomposition of
the light curves of the RR Lyrae stars to derive cluster parameters using
empirical relations. We find a cluster metallicity [Fe/H]_ZW=-2.01 +- 0.04, or
[Fe/H]_UVES=-2.11 +- 0.06, and a distance of 8.32 +- 0.20 kpc (using RR0
variables), 8.10 kpc (using one RR1 variable), and 8.35 +- 0.42 kpc (using our
SX Phoenicis star detection in M 30). Fitting isochrones to the CMD, we
estimate an age of 13.0 +- 1.0 Gyr for M 30.
