It is well known that the ionosphere can be highly disturbed in the auroral
and polar cap regions. However, efforts to quantify ionospheric effects on
high-frequency communications have concentrated mainly on lower-latitude r
egions. The Doppler and multipath sounding network (DAMSON) has been used i
n an extensive campaign to measure the channel characteristics on four path
s in the auroral region of northern Scandinavia. The conditions observed in
dicate that robust data modems, used when less-robust, higher-rate modems f
ail, are required up to 90% of the time. A detailed analysis of the propaga
tion parameters indicates that these modems, designed to operate in these r
egions, should be able to operate when the Doppler spread exceeds 40Hz and
the multipath spread is greater than 11.5ms. Multiple propagation modes are
common, especially between the lowest and maximum usable frequencies. The
distribution of the received signal power in these cases is examined, and i
t is concluded that laboratory simulations used for robust-modem evaluation
should include channel models with dominant modes.