Re: Boston FMs

["Mark Casey" <map@map.com>]

Larry gave a terrific concise explanation for most FM DX occurances.
Here's to "Chiming in" with  just a few comments on the practical difference
between "TROPO" and "E-SKIP"

With "Tropo" you will usually hear most everything in between your location
and the farthest distance the "tropo" is conducting. Tropo has been
experienced on the FM band as far as Florida, but this is rare. "Tropo" may
last for hours and/or several days, and, as Garrett noted, is usually best
from just after sunset, then through the night, and through early AM

With "E-Skip" you will usually hear strong signals in a 100-300 mile segment
of the area at a distance of from 700 to 1500 miles, and little or nothing
in between.  "E-Skip" is usually short-lived, from a few minutes to several
hours and can occur at any time, but afternoons are the most common time. If
you hear FM BCB "E-Skip" at a shorter distance than 1000 miles, that usually
means that higher frequencies will be affected--so then it's time to check
VHF TV Channels 7-13 for DX.
Large areas of thunderstorms in the interior of the East Coast or Midwest
may be a precursor or indicator for "E-Skip"

Note: Tropo" and "E-Skip" are sometimes experienced concurrently.

Check the Hepburn Tropo forecast for a real neat propagation map. I don't
have the current url, but if you search for "Hepburn Tropo" it should be
easy to locate.

Now if we're lucky enough, maybe we'll have comments on "F2-Skip" in another
9 or 10 years, when the sunspot cycle starts to peak again.

Mark Casey
map@map.com

>
> 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
>
>