Re: Boston FMs

[Larry Weil <kc1ih@mediaone.net>]

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 
explanation):

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