Robert Bass said:
Long-haul ducts exist, but this wasn't one of them.
http://en.wikipedia.org/wiki/TV-FM_DX
General characteristics of a duct:
- Affect higher frequencies, like TV channels 7 and up, including UHF.
- Weakest, least likely during daylight hours. Best around sunrise and shortly after.
- Relatively long-lived. May open around sunset and remain open for a few hours after sunrise.
- Usually elevation-sensitive. If the "target city" has some stations on high towers & others at lower elevations, you often hear only the higher stations, even if the lower ones are more powerful. Or vice-versa.
- Fading is relatively slow and shallow. It will take 30 seconds to a minute for one station to fade out and be replaced by another.
- Relatively weak signals. Ducted signals usually won't be strong enough to clobber locals.
- Form best over water. Houston<=>Tampa, for example, is a common tropo ducting path.
- Related to weather. Most likely when an approaching cold front is about to push off a stable area of high pressure.
- Form over a single straight path. If there's a DFW<=>Pensacola path, there probably isn't a Pensacola<=>Cincinnati path at the same time.
General characteristics of E-skip:
- Affect lower frequencies. **THERE HAS NEVER BEEN E-SKIP ON UHF.** (in other words, if there's DX on UHF TV, it's **NOT** E-skip) Skip affecting TV channels 7-13 is EXTREMELY rare - many lifelong DXers have never seen it. E-skip ALWAYS affects lower TV channels 2-6 first.
- Most likely from late morning through mid-afternoon. Least likely in early mornings. (just when tropo is most likely)
- Short-lived. FM openings rarely last more than an hour. (yesterday was a very pleasant exception!)
- Usually NOT elevation-sensitive. If you get one station from a city, you'll probably get *all* the stations from that city regardless of antenna height. (and, in many cases, regardless of power)
- Fading is deep and rapid. One station may fade out completely in a second or two, to be completely replaced by another - and then to promptly return a second later.
- Relatively strong signals. Skip signals were covering several Nashville locals here yesterday. (20-25mi. away)
- Paths are independent of the geology underneath. Houston<=>Tampa is a common skip path, but so is Houston<=>Tucson.
- Form over a common midpoint zone. With a midpoint zone over Columbus, Georgia, you might have skip over Miami<=>Nashville, Charleston SC<=>Jackson MS, and Charlotte<=>New Orleans paths.
- Not dependent on weather at the endpoints. (there is some evidence that severe weather at the *midpoints* triggers E-skip)
So while Miami<=>DFW is not a completely impossible tropo path, the preponderance of the evidence suggests that what happened yesterday was in fact E-skip.
;D