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Re: Boston FMs

At 07:58 PM 8/20/01 -0700, Matthew Osborne wrote:
>Whats the technical term I've heard used on this list
>for that before, the tropo?  And would somebody mind
>responding to me off list if necessary to explain
>exactly how this tropo works, when it "opens up" and
>whatnot.  I'm a bit confused about it

The simple version (I'm sure someone will chime in with the more complex 

Tropo is short for tropospheric ducting.  It is caused by weather 
conditions, most notably temperature inversions that form along a weather 
front.  It creates a duct along the front, which has the effect of ducting 
a VHF or UHF signal a much greater distance than it would normally be heard.

The typical distance that a tropo will conduct a signal is 200 to 500 
miles.  If you hear a VHF or UHF signal at a much greater distance, it is 
probably sporadic e-skip, which involves higher levels of the 
atmosphere.  The cause of sporadic e is unknown, although wind shears are 
suspected to be involved.  Sporadic e reception is known to be over ranges 
of 1000 to 1500 miles.
Larry Weil
Lake Wobegone, NH