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![]() "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.. |
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