Thursday, May 31, 2007

E-Skip

Skip normally refers to the distant reception of AM radio stations via signal echos reflecting off the ionized night troposphere. Its present in other bands, in other contions as well though. It's assumed by many to never occurr in the FM band. It does happen, but in for different reasons and with a different cause. But the end result is the same, a long single hops of E-skip can travel 1500 miles.

E-skip is more often mentioned in context with television DX. But it can occurr in the FM band as well. E-skip occurs only when patches in the E layer of the ionosphere become ionized. The E-skip patch must be at approximately the midpoint between the transmitter and receiver. Sometimes the patches failry stationary, but also can move at speeds of several hundred miles per hour. Movement is typically in a straight line but not always. There can also be multiple seperate E-skip patches allowing for "double skip"or double hop to occurr. More here.

The cause of E-layer ionization is not precisely known. The multiple theories disagree on cause but low pressure areas and thunderstorms are both popular culprits. Surface weather has a poor causal relationship, it's more likely symtomatic of the mutual cause... Neat E-layer map here.
An E-skip episode usually up to a few hours and usually in the middle of the day. The season for E-skip peaks in the months of May and June. In coastal areas, that same season also induces tropospheric ducting, which can carry signals hundreds of miles. Try not to confuse the two. maybe I shoudl expalin that tomorrow...