  The minimum and the mean bandwidth of individual narrowband spikes in two
events in decimetric radio waves is determined by means of multi-resolution
analysis. Spikes of a few tens of millisecond duration occur at
decimetric/microwave wavelength in the particle acceleration phase of solar
flares. A first method determines the dominant spike bandwidth scale based on
their scalegram, the mean squared wavelet coefficient at each frequency scale.
This allows to measure the scale bandwidth independently of heuristic spike
selection criteria, e.g. manual selection. The major drawback is a low
resolution in the bandwidth. To overcome this uncertainty, a feature detection
algorithm and a criterion for spike shape in the time-frequency plane is
applied to locate the spikes. In that case, the bandwidth is measured by
fitting an assumed spike profile into the denoised data. The smallest FWHM
bandwidth of spikes was found at 0.17 % and 0.41 % of the center frequency in
the two events. Knowing the shortest relevant bandwidth of spikes, the slope of
the Fourier power spectrum of this two events was determined and no resemblance
to a Kolmogorov spectrum detected. Additionally the correlation between spike
peak flux and bandwidth was examined.
