  The aim of the Air Microwave Yield (AMY) experiment is to investigate the
Molecular Bremsstrahlung Radiation (MBR) emitted from an electron beam induced
air-shower. The measurements have been performed with a 510 MeV electron beam
at the Beam Test Facility (BTF) of Frascati INFN National Laboratories in a
wide frequency range between 1 and 20 GHz. We present the experimental
apparatus and the first results of the measurements. Contrary to what have been
reported in a previous similar experiment~\cite{Gorham-SLAC}, we have found
that the intensity of the emission is strongly influenced by the particular
time structure of the accelerator beam. This makes very difficult the
interpretation of the emission process and a realistic extrapolation of the
emission yield to the plasma generated during the development of an atmospheric
shower.
