A Beginner's Guide to E-skip

I have been a DXer on the Medium Wave (AM) radio band since the 1960's.   During that time, I have logged nearly 1600 stations which I could identify, and until the early 1990's, attempted to get printed verifications (QSLs) from each station which I had heard.   As radio stations focused more on their financial bottom line and began curtailing their responses to people like myself, I began to realize that I was spending time, money and energy on something that was becoming harder and harder to get.   During this entire period, AM was for baseball games and DXing, and FM was for music.   For more than forty years, I listened to FM on a regular basis, but I never considered DXing FM, because I never heard anything outside my immediate area.   If FM was limited to line of sight, and was there to serve the area that could be covered by line of sight, there wasn't much point.   That logic process crashed and burned on May 27, 2005.

I had just picked up a hamburger, and not feeling like heading back home yet, I parked under a tree and tuned to my favorite rock station (KFOG/104.5 in San Francisco).   Something wasn't right ... they were talking religion.   I tried KOZZ/105.7 in Reno ... but I was getting a weather forecast for Sterling, wherever that was.   It was about forty degrees cooler in Sterling than where I was, but I still had no clue where Sterling was.   Next try was KRQR/106.7 in Orland.   They didn't come in well, but they played good music.   Instead, I found out about a 4-car wreck on I-25 in Fort Collins.   I knew where that was, so I decided that the hamburger would be no worse in a few minutes than it then.   I started taking notes ... 106.7 was definitely Fort Collins or Denver.   Back to 105.7 ... they finally identified themselves as KPMX in Sterling.   I knew there was a Sterling in northeastern Colorado.   Huh!  Over to 104.5 and the top of the hour was coming.   There's always IDs at the top of the hour.   The show came to an end, and anticipation mounted.   I don't remember the exact words, but it was something to the effect of the "Bott Radio Network serving God's word to western Nebraska."   That's my paraphrase, and not a quote.   I couldn't wait to tell somebody, but most people thought I was crazy for spending so much time listening to the radio and choosing to spend most of my time on the stations that sounded the worst.

I soon found out that what I heard was called E-skip, or Sporadic E as some people call it.   I also found out that if it starts, it starts at the bottom of the band.   Had I known, I would have heard a lot more stations from 88.1 all the way up to where I discovered it at 104.5.   At the same time, I was elated to have heard it, and kicking myself in the butt for not searching elsewhere in the band.

That began my search for E-skip.   I asked a million questions about skip to people who were familiar with it, and while some questions could be answered, most could not.   That was a little over a year ago, am I am still fascinated by it.   You can find many internet articles on the subject, and I won't try to condense or paraphrase other peoples' research.   Furthermore, I am not professing to be an authority on the subject (to put it mildly).   When I encountered E-skip, I had no clue who to ask questions of, and no real idea of how to form a question on something which at the time was completely inexplicable to me.   I now have a network of people who I can ask questions, bounce ideas off of, compare notes, and when I'm lucky, brag.   My goal here is to provide some basic information on something that is still magical to me.   I don't have explanations...I have observations.   Here's what I know...

• E-skip is more common in the spring and summer, but is not limited to the warmer months.  In the northern hemisphere, activity is basically two months either side of the summer solstice (June 21), with a smaller peak around the winter solstice (December 21).  In the southern hemisphere, the periods are opposite, as are the seasons.  Equatorial regions are active throughout the year.
• E-skip is more common in the daytime than it is at night.
• E-skip is more common in the eastern and midwest parts of the US than it is in the west, though the Pacific Northwest region is very active.
• E-skip is based on special cloud types that reflect radio signals.
• E-skip can be influenced by tornadoes and electrical storms that highly charge the atmosphere.  Skip is not guaranteed by storms, but storms may help to create the condition.  In the example I stated above, a check of thunderstorm web sites showed a solid line of intense thunderstorms across Nevada and Utah at the exact heading of my three distant receptions.  There have also been many occasions where thunderstorm patterns did not yield any skip activity.
• The special cloud may be equidistant between the transmitter and reception sites.  It may also be tilted, allowing the cloud to be closer to either the transmitter or receiver.
• The stations that are affected by these clouds are typically in the range of 500-1400 miles away.
• The stations are focused in a rather small geographical area.
• Listeners in location A can hear stations from location B during E-skip conditions.  At the same time, listeners in location B will be able to hear stations in location A if the cloud is uniform.
• There are typically numerous locations affected at any one time by a cloud.  If you watch the skip maps (referenced on the links page), you will see that when skip begins, there is a central location at which many paths cross.  That's where the cloud is!  For each line that appears on a map, there is a "Location A and B" associated with that line.
• Clouds move!  Your session may continue with an ever-changing cast of characters as the cloud moves.
• E-skip conditions may disappear quickly if the area reflected by a cloud moves into a rural area, and conversely, may appear in the same manner if the reflected area moves from rural to urban.

• As it pertains to FM, E-skip begins at lower frequencies (below TV channel 2), and may rise through the FM band (88-108 MHz) and beyond.
• The highest frequency affected by E-skip is called the MUF (Maximum Usable Frequency).
• When E-skip reaches higher MUFs, all frequencies below the MUF are also activated.
• Stations at or near the MUF usually sound very poor due to instability
• Stations heard via E-skip are relatively stable and are of good to excellent audio quality, though their volume may rise and fall in slow cycles.
• MUF is subject to rapid change.  It is not uncommon for the MUF to rise and/or fall 10-20 MHz in just a few minutes.
• Stations coming in via E-skip can easily overtake a frequency that is empty or used by a weak-to-average semi-local station.
• Stations coming in via E-skip will likely be in contention with a strong semi-local station for "ownership" of the frequency.  It's not pretty!
• Stations coming in via E-skip will likely not be able to overtake a frequency with a strong local station.
• Transmitter power is apparently not an issue, as I have heard stations via skip with power as low as 950 watts.
• Special receiving equipment is not required.  I used a stock car radio for four months until I bought a more sensitive Blaupunkt car radio.  I still use that as my primary FM DX radio.