"starman" wrote in message
...
The mountains might be the geographical boundary but we shouldn't assume
they are the actual cause of MW signal attenuation from the west coast
at night. Long distance MW propagation at night is mainly via skywave
refraction from the ionosphere, just like shortwave. A range of
mountains is not going to interfere with what is taking place 50-miles
or more above them. This is not the case in the day when MW propagation
is primarily via groundwave. Then the mountains may well have an effect.
We have to consider the nature of the geology (particularly the soil)
west of the mountains and how this may affect MW propagation towards the
east at night.


The greatest boundary to bi-coastal AM DX is not geographical at all.. but
purposeful. Stations that have high power at night have very directional
arrays that protect other stations on the same frequency. Most on the west
coast have N-S or similar patterns that keep them from being heard on the
east coast. For instance, KOMA (or whatever they are this week) in OKC and
KKSN in Portland, OR must protect each other's nighttime coverage. (both are
1520 KHz).

An interesting point... I have yet to see a directional array here in the
ROK.. and it shows.. at night there are so many stations fighting over any
given frequency that it numbs the mind. Most of the winners are Russian and
Chinese. I have only ever heard one Japanese MW station here..