Iowa DX
Tropo is loads of fun for radio geeks of all kinds. ;D
Those south of Des Moines (particularly on the hills near St. Charles and Martensdale where you're far enough away to avoid Life 96.1's adjacent channel interference) might wish to try for 96.3 KTTB-Glencoe, MN. It runs an urban format known as "B96", and is an interesting signal for a number of reasons.
First off, it's the Rimshot from Hell -- Glencoe is over 40 miles straight-line west of downtown Minneapolis, and about 50 from downtown St. Paul. Despite serious multipath in downtown St. Paul (especially Capitol Heights and Mounds Park) and even in parts of Minneapolis, the station regularly shows around 3.5 (12+) in the Arbs. Secondly, it's 100kW, but at only 578' HAAT. Thirdly, it's on a frequency that's VERY clear in the area... which causes it to be receivable in a number of spots on I-35, sometimes strongly enough to bring in and hold a stereo pilot. (Under regular conditions, I've heard it as far as Iowa Exit 34 for Osceola. With even moderate tropo, I've logged it at Van Wert, and my all-time record for it is Missouri Exit 110 for Eagleville!) I've often wondered if its low height might actually be an ADVANTAGE for extreme DX of this kind, as the signal peeks through in a number of places one really wouldn't expect -- there are *valleys* around mile 42 where the signal outperforms high areas closer to the 5/65 interchange. Perhaps it's hitting the ground at just the right angle to be detected by a car antenna. In any event, the tropo ought to make B96 an even more likely catch... unless, of course, it's favoring the south, in which case they'll probably be canceled by Keokuk.
In the other direction, KAZR-Pella/Des Moines "Lazer 103.3" is a regular catch in the southern Twin Cities suburbs when tropo's in -- and sometimes when it's not, if you park your car in JUST the right spot in Prior Lake or Lakeville. (The FCC calculator says this signal is one dB BELOW a microvolt at my folks' place in that area... being the nerd I am, I just about fainted when that number popped up. ;D) And when tropo is quite good, the area will also receive 97.7 KCRR-Grundy Center, and Z98 from Sioux City (97.9).
MadSam -- I was also pretty shocked when I first heard that FM signals can also travel the extreme distances we normally expect from nighttime AM. Some of the engineering types on this board might be able to fill out the explanation a little bit better, but here's the basics for ya.
Tropospheric ducting ("tropo" for short) happens most often in June and July, when temperature inversions are common. (Ordinarily a warm air mass naturally rises, but it will occasionally be trapped closer to the ground and eclipsed by colder masses.) This leads to the formation of a "duct" that features ideal conditions to trap and repeatedly reflect VHF signals (i.e., signals around the frequency of TV channels 2-6, and FM broadcast.) The signals generally bounce through the duct and come down to your radio at distances of around 300 miles... sometimes further. (Some folks on this board have received signals from 550 miles away via tropo!) Tropo tends to happen first at lower frequencies -- i.e., around TV channel 2 (54 MHz) -- and rise toward the FM band as tropo-causing conditions get more extreme. Thus, the best FM tropos are somewhat more likely on the low end of the band.
The REALLY insane FM travel owes to a phenomenon known as E-skip, in which FM signals somehow get trapped in the "E-layer" of the atmosphere, and refracted (i.e. bent) at bizarre angles that cause them to return to Earth up to 1500 miles away (but typically around 1000). I'm not as familiar with how this process occurs... nor do I know, aside from distance, how to tell a tropo signal from a skip one... perhaps there are some experts reading the forum who could fill us in.
