  We present a study of the heavy-light spectrum and of the D- and B-meson
decay constants. The results wer e obtained in the quenched approximation, by
using the non-perturbatively improved Clover lattice action at beta=6.2, with a
sample of 100 configurations, on a 24^3 x 64 lattice. After a careful analysis
of th e systematic errors present in the extraction of the physical results, by
assuming quite conservative discretization errors, we find f_Ds=231 +/-
12^{+6}_{-1} MeV, f_D = 211 +/- 14^{+0}_{-12} MeV, f_Ds/f_D=1.10(2), f_Bs = 204
+/- 16^{+28}_{-0} MeV, f_B = 179 +/- 18^{+26}_{-9} MeV,
f_Bs/f_B=1.14(3)^{+0}_{-1}. Our results, which have smaller discretization
errors than many previous estimates at fixed value of the lattice spacing $a$,
support a large value of f_B in the quenched approximation.
