The mode of propagation that brings all of your local stations to you is called
"Groundwave" (GW). You can get stations around 0-50 miles away via GW. Mostly,
stations that you get by GW come in crystal clear full stereo for radio, or with
a clear color picture for TV, but during some strong atmospheric conditions any
local station might be overpowered by a faraway station, as explained in the other
The mode of propagation that brings all of the near, but out-of-town stations
to you is called "Extended Groundwave" (XGw). On average XGw brings in stations
50-100 miles away. Most of the time the stations brought in by XGw are either
in staticy mono or clear mono quality (staticy black and white or clear black
and white quality for TV), but depending on atmospheric conditions XGw could bring
in the same stations as clear as your local stations, with full stereo and a clear
color picture for TV. But, like Groundwave, these stations are suspectable to
being overpowered by the other modes of propagation, discussed below.
Another mode of propagation, Tropo (Tr), is directly related to weather, with
the influence of a high pressure area required for it to happen. With a temperature
inversion, with warm air meeting cold, a low level conduit forms in the tropospheric
layer of the atmosphere that causes FM and television signals to travel hundreds
of miles. It's most likely to happen during early evening until a little bit after
local sunrise. It's not unusual for tropo conditions to last for several days
over a wide area. Tr usually brings in stations 100-300 miles away, but depending
on how strong it is, might even bring in stations up to 1000+ miles away. Stations
brought in by Tr usually come in staticy or clear mono quality (or staticy black
and white or clear black and white for TV). But, if it's a strong opening, the
stations can come in as clear and in stereo (or in clear color for TV) as your
local stations, and they might even overpower some your local stations, with no
trace of the local station's signal at all.
Being the most exciting form of signal propagation, Sporadic E-Skip (Es), occurs
when a FM signal strikes a highly ionized patch of the E layer of the atmosphere
and the signal is reflected back down to Earth. Most of the time Es occurs during
the months of May, June, July, and August at 7:00AM-Noon, and 2:00PM-6:00PM, but
it could happen during any time of any day of the year. Es will reflect a signal
500-1,500 miles. But on rare occasions, Es "clouds" will line up to provide a
double hop, producing reception of stations 2,000-3,000 miles away. Es can come
in with rapid fades, and you'll often find 2 or more stations fighting it out
for control of the frequency. The stations you receive via E-skip will generally
come from the same area, but beware... Es clouds tend to move around. For example,
DXing from the Midwest,you might have a cloud move so that your opening starts
out in the northeast and winds up in Florida over the course of several hours.
From what I have experienced before with Es, the area that you are getting stations
from most likely is experiencing some sort of severe weather, like thunderstorms,
hurricanes, etc. If thats the case the station will usually put up some sort of
warning on the screen, may it be a map of the station's viewing area, or just
scrolling words going across the top of the screen. That is a very helpful way
for us DXers to identify the station we are getting because it will have the map
of the station's viewing area on the screen. The best way to keep tabs on Es is
to check your open television channels 2, 3, 4, 5, and 6, the lower the better.
These channels will be the first to be affected by Es, as they are lower in frequency
than FM, which falls between channels 6 and 7. For example, if you don't have
any local television stations on channel 2, and you start to see rolling black
bars or see 'co-channel interference' (an example shown in the 'screenshots' section
of this website, then you have Es!
Being the mode of propagation that is often the most frustrating, Meteor Scatter
(Ms), can affect the entire FM band, but it's best to park on an open frequency
and see what happens. Ms usually will bring in signals in the 200-1,200 mile range.
Most meteors that enter Earth's atmosphere burn up, leaving a visible trail. FM
signals reflect off this trail, giving DXers usually anywhere from 1-10 seconds
of audio. Obviously, it requires a lot of patience! During the big meteor showers,
like the Perseids in August, you'll hear several signal bursts each minute.
FM signals can actually reflect off the aurora borealis, by a propagation mode
called Aurora Scatter (Au), with catches possible in the 300-800 mile range (and
sometimes beyond). It's far more likely to be accessible to northern DXers. If
you hear about a solar flare or increased solar activity, be on the lookout for
Au. Signals by this mode tend to be slightly distorted.
Skywave (SW), this mode only affects AM radio reception. Signals reflect off the
E-Layer of the atmosphere like in Sporadic E-Skip, bringing in stations 300-1500
miles away on average to you, but unlike E-Skip, SW happens every night after
sunset until a little after sunrise and not every now and then, and you usually
get the same stations via SW every night, but don't be suprised if you get some
different stations once and a while!
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