  The NSF's Karl G. Jansky Very Large Array (VLA) is used to observe 122
magnetic cataclysmic variables (MCVs) during three observing semesters (13B,
15A, and 18A). We report radio detections of 33 stars with fluxes in the range
6--8031 uJy. Twenty-eight stars are new radio sources, increasing the number of
radio detected MCVs to more that 40. A surprising result is that about
three-quarters (24 of 33 stars) of the detections show highly circularly
polarized radio emission of short duration, which is characteristic of electron
cyclotron maser emission. We argue that this emission originates from the lower
corona of the donor star, and not from a region between the two stars. Maser
emission enables a more direct estimate of the mean coronal magnetic field of
the donor star, which we estimate to be 1--4 kG assuming a magnetic filling
factor of 50%. A two-sample Kolmogorov-Smirnov test supports the conclusion
that the distribution function of radio detected MCVs with orbital periods
between 1.5-5 hours is similar to that of all MCVs. This result implies that
rapidly-rotating (Pspin < 10 days), fully convective stars can sustain strong
magnetic dynamos. These results support the model of Taam & Spruit (1989) that
the change in angular momentum loss across the fully convective boundary at
Porb = ~3 hours is due to a change in the magnetic field structure of the donor
star from a low-order to high-order multipolar field.
