  We obtained time-series radial velocity spectroscopy of twenty cataclysmic
variable stars, with the aim of determining orbital periods P_orb. All of the
stars reported here prove to have P_orb > 3.5 h. For sixteen of the stars,
these are the first available period determinations, and for the remaining four
(V709 Cas, AF Cam, V1062 Tau, and RX J2133+51) we use new observations to
improve the accuracy of previously-published periods. Most of the targets are
dwarf novae, without notable idiosyncracies. Of the remainder, three (V709 Cas,
V1062 Tau, and RX J2133+51) are intermediate polars (DQ Her stars); one (IPHAS
0345) is a secondary-dominated system without known outbursts, similar to LY
UMa; one (V1059 Sgr) is an old nova; and two others (V478 Her and V1082 Sgr)
are long-period novalike variables. The stars with new periods are IPHAS 0345
(0.314 d); V344 Ori (0.234 d); VZ Sex (0.149 d); NSVS 1057+09 (0.376 d); V478
Her (0.629 d); V1059 Sgr (0.286 d); V1082 Sgr (0.868 d); FO Aql (0.217 d); V587
Lyr (0.275 d); V792 Cyg (0.297 d); V795 Cyg (0.181 d); V811 Cyg (0.157 d); V542
Cyg (0.182 d); PQ Aql (0.247 d); V516 Cyg (0.171 d); and VZ Aqr(0.161 d).
Noteworthy results on individual stars are as follows. We see no indication of
the underlying white dwarf star in V709 Cas, as has been previously claimed;
based on the non-detection of the secondary star, we argue that the system is
farther away that had been thought and the white dwarf contribution is probably
negligible. V478 Her had been classified as an SU UMa-type dwarf nova, but this
is incompatible with the long orbital period we find. We report the first
secondary-star velocity curve for V1062 Tau. In V542 Cyg, we find a late-type
contribution that remains stationary in radial velocity, yet the system is
unresolved in a direct image, suggesting that it is a hierarchical triple
system.
