  We combine surveys of the radio sky at frequencies 22 MHz to 1.4 GHz with
data from the ARCADE-2 instrument at frequencies 3 to 10 GHz to characterize
the frequency spectrum of diffuse synchrotron emission in the Galaxy. The radio
spectrum steepens with frequency from 22 MHz to 10 GHz. The projected spectral
index at 23 GHz derived from the low-frequency data agrees well with
independent measurements using only data at frequencies 23 GHz and above.
Comparing the spectral index at 23 GHz to the value from previously published
analyses allows extension of the model to higher frequencies. The combined data
are consistent with a power-law index beta = -2.64 +/- 0.03 at 0.31 GHz,
steepening by an amount Delta beta = 0.07 every octave in frequency. Comparison
of the radio data to models including the cosmic ray energy spectrum suggests
that any break in the synchrotron spectrum must occur at frequencies above 23
GHz.
