> Can someone give me a primer on what tropo is? I assume
> E-skip is a signal bouncing off the E layer of the
> ionosphere. But how do you tell the difference between the
> two?
Sometimes, you can't tell.
But usually...
E-skip: lasts for a few minutes to an hour or two
Tropo: lasts for several hours
E-skip: brings in stations no *closer* than about 700 miles and as far as 1,400
Tropo: brings in stations as close as 50 miles but no *further* than 400
E-skip: happens in mid-morning and early evening, lulls at noon and night
Tropo: happens in late evening through early morning, lulls during daytime
E-skip: starts at TV channel 2 and moves up in frequency, through 88 to 108
Tropo: starts at all frequencies at once but not as likely to affect low TV
E-skip: has deep, fast fading. Fade cycles last a few seconds.
Tropo: has shallow, slow fading. Fade cycles last a few minutes.
These are all generalizations. There will be exceptions. The one difference that's hard-and-fast is that E-skip NEVER affects UHF. If you're getting distant UHF-TV signals, then it's tropo. Unless you have tropo and E-skip at the same time!
> Are these great DX conditions occuring now on FM
> unpredictable?
If you mean E-skip, yes, they're unpredictable. Science has some ideas about what may cause it, but there is no one theory that's widely accepted. In very general terms, E-skip is more common in mid-morning and early evening from mid-May through about now. But you can't predict *which* June mornings will be skip-filled.
Tropo is well-known to be related to predictable weather effects.
http://home.cogeco.ca/~dxinfo/tropo.html is a website operated by a Canadian meteorologist; it provides a tropo forecast. In general, tropo is more likely during extended periods of stable high pressure.
> Other than the ionosphere, what other conditions affect the
> FM band?
Of course, the troposphere, which is affected by weather.
Meteorites entering the earth's atmosphere generate reflective trails as they burn up. This causes basically a VERY brief E-skip opening. (i.e., as short as a tenth of a second and as long as several seconds) Attentive DXers can take advantage of this "meteor scatter". Of course, this kind of thing is much more common during "meteor showers".
The aurora borealis (and australis) can refract radio signals. There's usually quite a bit of distortion but sometimes one can still identify what they're hearing. South of Chicago, this kind of propagation is EXTREMELY rare but north of there it's worth looking for.
> Finally, what is the closest amateur radio band to the
> commercial FM frequencies?
I suppose the FM broadcast band falls roughly midway between the 50-54MHz "6-meter" and 144-148MHz "2-meter" bands. E-skip is far more likely on 6 meters; tropo more likely on 2. The U.K. and a handful of other European countries have a "4-meter" band near 70MHz which is considerably closer to the FM broadcast band.
