  We investigate the spectra, material properties, and orbital distribution of
millimeter- to decimeter-sized meteoroids. Our study aims to distinguish the
characteristics of populations of differently sized meteoroids and reveal the
heterogeneity of identified meteoroid streams. We verify the surprisingly large
ratio of pure iron meteoroids on asteroidal orbits detected among mm-sized
bodies. Emission spectra and multi-station meteor trajectories were collected
within the AMOS network observations. The sample is based on 202 meteors of -1
to -14 magnitude, corresponding to meteoroids of mm to dm sizes. Meteoroid
composition is studied by relative intensity ratios of Na, Mg, and Fe.
Heliocentric orbits, trajectory parameters, and material strengths inferred
from empirical $K_B$ and $P_E$ parameters were determined for 146 meteoroids.
An overall increase of Na content compared to the population of mm-sized
meteoroids was detected, reflecting weaker effects of space weathering
processes on larger meteoroids. We report a very low ratio of pure iron
meteoroids and the discovery of a new spectral group of Fe-rich meteors. The
majority of meteoroids on asteroidal orbits were found to be chondritic.
Thermal processes causing Na depletion and physical processes resulting in
Na-rich spectra are described and linked to characteristically increased
material strengths. Numerous major and minor shower meteors were identified in
our sample, revealing various degrees of heterogeneity within Halley-type,
ecliptical, and sungrazing meteoroid streams. Our results imply a scattered
composition of the fragments of comet 2P/Encke and 109P/Swift-Tuttle. The
largest disparities were detected within the $\alpha$-Capricornids and
$\delta$-Aquarids. We also find a spectral similarity between $\kappa$-Cygnids
and Taurids, which could imply a similar composition of the parent objects of
the two streams.
