  Spectral Spatial Fluctuations (SSF) of the Cosmic Microwave Background
Radiation (CMBR) temperature are considered as a result of an interaction of
primordial atoms and molecules with CMBR in proto-objects moving with peculiar
velocities relative to the CMBR. Expected optimistic values of $\Delta T/T$ are
2x10^{-5}--2x10^{-6}$ for SSF caused by HeH$^+$ at z =20-30 which are possible
redshifts of early reionization scenario. The bandwidth of the lines is 0.1-2%
depending on the scale of proto-objects and redshifts. For the SSF search CMBR
maps in different spectral channels are to be observed and then processed by
the Difference method. Simulation of the experiment is made for MSRT (Tuorla
Observatory, Finland) equipped with a 7x4 beam cryo-microbolometer array with a
chopping flat and frequency multiplexer providing up to 7 spectral channels in
each beam (88-100 GHz). Expected $\Delta $T/T limit in the experiment is 2x10
$^{-5}$ with 6'-7' angular and 2% frequency resolution. Simulation shows that
SSF may be recognized in the angular power spectrum when S/N in single
frequency CMBR maps is as small as 1.17 or even something less for white noise.
Such an experiment gives us a possibility to set upper limit of SSF in MM band
and prepare future SSF observations.
