Understanding 10 Meter Sporatic-E

By "James R. Duffey" <jamesd1@flash.net>

In the late spring and early summer 10 meters comes alive with signals, some strong, some weak, most within 1400 miles; a few from farther out. Signals can come and go quickly or stay in all day. Signals can be very strong or extremely weak. The signals can all be from the same geographical location, or they can be spread out all over the country.

This happens even if the solar flux is low. What is this propagation phenomena? It is sporadic-E skip, sometimes called E skip, and sometimes just short skip. Sporadic-E skip is caused by large patches of ionization in the E-layer of the ionosphere. The exact cause of these patches is not well known, but they are associated with wind shear and some think they are connected with high towering thunder storms. These patches of ionization are not caused by solar activity as is the ionization in the F layer that we are more familiar with.

Since the E-layer is about 70 miles high, single skip is limited to about 1400 miles (this can be easily proved and is left as an exercise to the reader). Double skip is possible, but because of the patchy nature of the ionization, double skip requires two patches at the right distance apart, which are not always readily available.

E-layer skip occurs most often from 0900 to 1100 and 1900 and 2300 local time (not UTC!), although it can occur at any time of the day. It is most common between Mid-May and Mid-July, with a secondary season between Mid-December and January. So look for it on mornings, and evenings during Christmas break.

The best way to find an opening is to monitor 10 meters. There are a number of beacons scattered around the country between 28.2 and 28.3 MHz. Often these beacons can be heard weakly when the band is otherwise closed. When the band is open at all there is almost always someone on 28.4 MHz SSB, so that is a good frequency to check first. No I don't know why most hams prefer round numbers. The Ten-Ten crowd hangs out around 28.345 so that is also a good place to check. Those paper chasers are always alert to a band opening and call CQ with the slightest encouragement. [Note: another major 10 meter SSB frequency is 28.495 Mhz.]

For some reason there is little CW activity during Sporadic-E 10 meter openings, but Novices, not knowing this, call anyway. My experience is that I am more likely to find a CW contact on the 10 Meter Novice band than in the General portion of the band during a sporadic-E 10 meter opening.

There are a number of 10 meter repeaters every 20 KHz above 28.6, and as these are always on they can also be a good indicator of whether or not the band is open. Many have antennas that are quite high so they are often heard when nothing else on the band is heard.

The CB channels immediately below the 10 meter band [the old 11 meter ham band] are usually very busy during sporadic-E. If you listen closely you can even hear some interesting "explanations" for the phenomena.

Call CQ if you don't hear any activity.

The ionization patch, once generated, will drift to the north east at a speed of 180 mph. The ionization patch is what reflects your signal and is at the midpath of your contact. You can use this to predict who you will work next. Often an ionization generating spot will generate several patches, so you will notice cycles. From my New Mexico location a Sporadic-E session might start with New Orleans coming in loud, then Arkansas, St. Louis, and if the cloud lasts a long long time, Omaha and Siuox Falls. Often I can hear several of these locations simultaneously, indicating that several ionized patches are present.

The location of the generating source moves east at about 12.5 degrees per day, so if you had short E skip in the morning you may have long E-Skip in the evening, and if you had short E-skip in the evening you may have long skip in the morning. If you worked to the west yesterday, you may work to east today or tomorrow. So, if I hear New Orleans today, I may hear Alabama from the same patch tomorrow. If I work California, I know that there are probably several more days of E-skip to come, and I will plan my future activities accordingly.

When the skip becomes very short, the ionization is very dense and propagation at the next higher band is possible. So if I hear Dallas working San Antonio on 10 M, I know I have a good shot of working somewhere in Dixie on Six. Also if 10 meter is open on Sporadic-E; the 12 and 15 meter bands are also open, and maybe 17 meters and 20 meters as well, but with shorter skip. If you need those close in states for WAS this is a good time to try for them.

If you want more information on Sporadic-E, look at the ARRL publication; "Beyond Line of Sight". Also, the VHF column in QST often has hints on working Sporadic-E on 6 meters which apply to 10 meters as well. These are usually in the May and June issues. When it comes to Sporadic-E, 10 meters is a VHF band, not an HF one.

James R. Duffey KK6MC/5; Grid DM65
30 Casa Loma Road
Cedar Crest NM 87008

An extensive network of beacons is maintained around the world to help spot openings on bands like 10 and 6 meters. Here is some information on the beacon network:

HF Beacons

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