  We analyzed the band splitting of a Type II radio burst observed on 1997 May
12 by ground- and space-based radio spectrometers. Type II radio emission is
the most evident signature of coronal shock waves and the observed band
splitting is generally interpreted as due to plasma emission from both upstream
and downstream shock regions. From the inferred compression ratio we estimated,
using the magnetohydrodynamic (MHD) Rankine-Hugoniot relations, the ambient
Alfven Mach number. By means of the electron density obtained by inverting
white-light polarized brightness (pB) coronagraph data and the shock speed
inferred from the Type II frequency drift, we finally derived a radial profile
for the magnetic field strength in the middle corona. The result was compared
with the field profile obtained in May 1997 (but above $\sim 5 R_{sun}$) with
Faraday rotation measurements of extragalactic radio sources occulted by the
corona. The power law of the form $B(r)$ = 3.76 $r^{-2.29}$ Gauss inferred in
that work nicely describes the combined set of data in a wide range of
heliocentric distances ($r$ $\sim$ 1.8 - 14 $R_{sun}$).
