Sunday, May 31, 2020

A Ham Radio Series 1 - Sporadic E Propagation

The reactions to my “Got a Question for You” post surprised me.  Mostly by the quantity; I don’t have a way to check but it’s in the top couple of comment generating posts I’ve ever put up.  Some of specific questions were a bit of a surprise, too.

One of the subjects that came up has a time sensitive aspect to it, so I’m going to take a look at  propagation; in particular E skip, or sporadic E.  It’s going on right now, as I write and we’re at or close to the peak time of the year for sporadic E; at least here in the northern hemisphere. 

As usual, let me start at the beginning for those who aren’t familiar with it.  Both references are to propagation in the E layer of the ionosphere.  The ionosphere is called that because the air density is so low that individual atoms are far from each other, far enough that energy from the sun, mostly UV radiation, can cause electrons to be stripped from some atoms, giving rise to both negatively charged free electrons and positively charged atoms that can stay separate for long times.  The density of the air is so thin that it takes a long time for collisions between these ions to neutralize them.

The ionosphere is characterized by layers, conventionally called the D, E and F layers – in order of height.  If solar energy is high enough, the F layer can split into two layers called (imaginatively enough) F1 and F2.


Because the ionization is driven by solar energy, the general rule is these layers appear in the daytime, and the highest levels of ionization are in the area where the sun is most intense; so midday and directly under the sun.  While the D layer getting denser during the day shuts down lower frequencies that tend to be open all night (say 160 through 30m), the higher frequency bands’ signals (20 to 10m) travel through the D layer to the F, so they open during the day and are shut down at night.  This isn’t like a switch, it’s a more gradual transition.  For example, it seems that 30 is intermediate between 20 and 40; most days it seems to open earlier than 40m in the afternoon, and close later in the morning than 40m.  Back around the Spring Equinox, I’d hear Australia on 30m – close to my sunset and their sunrise.

It’s probably generally known that solar activity - sunspots and higher Solar Flux Index – increases the density of the ionosphere, making the F layer propagation last longer into the night, sometimes completely overnight.  Bands that are only useful for local communications during sunspot minima can be open to somewhere in the world 24 hours a day at the peaks of the solar cycle.

E layer propagation is left out of that overview because it’s harder to fit in.  Sporadic E has been known for a long time, but that word “sporadic” in the name is an indication of the toughness of predicting when it will occur.  We know there’s no correlation between solar activity and Sporadic E; in fact, the last few years have made it seem that it could be inversely proportional to solar activity (my observation – I haven’t seen anyone else say this).  We know that the mechanism is fleeting clouds of sufficient density in the E layer, and that it tends to occur more at certain times of years than others (now in the northern hemisphere).  We know that it tends to form later in the day and linger into the evening; that is, you'd be more likely to find it at 3PM than 3AM (local time).  Finally, we tend to observe it on higher HF and lower VHF bands; 28 and 50 MHz are peak bands.  It happens on occasion on the 144 MHz band.  Hams have long noticed that sporadic E clouds seem to form above the tops of thunderstorms - long before mechanisms that could extend the charge into the ionosphere, such as red sprites or dark lightning were discovered.

3PM?  This is a plot of reported sporadic E contacts at 10:14 AM EDT, Saturday, on 6m.  Each arc is a reported contact between the two stations at the ends of the arc.  Most of those arcs are in places where it's 9:14 AM.  It’s impossible to read all the call signs in this screen capture; there’s simply too many.


The plot is from a website I visit regularly called DX Maps.  This link should bring up this display for 6m over the US as of the moment you go there - I think those reports stay there on the order of a half hour.

The area in the east central US is blanketed by reported contacts.  There are many arcs starting in the Caribbean, (Puerto Rico, Guadeloupe, St. Lucia, Trinidad) going into the states.  As I write this, 11 hours later, the map looked much the same.  The density of the red traces (reported as Sporadic E, although always hard to know) is down, but the distribution is similar.  A couple of days ago, the concentration of red traces was over the western states: Utah, Wyoming, Montana, Eastern Oregon and Washington and virtually nothing on the east side of the country.  In other words, the opposite of this.  Another day, the east coast was full of paths reported into Europe, still another was full of paths reported from the west coast into Alaska and then Japan.  26 hours later, that previous plot looked like this:  


You can see the propagation to Europe marked by dark red arcs is dense into the NW US, with some into Mexico.

They call it Sporadic E because it’s not dependable or particularly predictable; you kind of know something is likely to happen, but don’t know what that “something” is going to be. It varies all day every time.  We know late spring into early summer is better than mid summer or mid winter.  I’m not sure that doesn’t vary with where you are.  I’ve heard from a guy between my location and the Space Center that around the Winter Solstice in December, he has worked 6m into New Zealand.  Note that’s around the equivalent of our first day of summer in NZ, in terms of heat and constancy of sunshine.

Because of that unpredictability, it’s fair to ask what practical use Sporadic E is.  I know of no systems that rely on it.  For hams, it’s mostly a way to rack up novel contacts that we don’t or can’t get any other way.  The band I’ve been on, 6 meters, is just below the bottom of the old VHF TV Channel 2.  A few days ago, I had a contact with a guy in Spain on 6m.  That’s similar to (while different in important ways from) watching Channel 2 TV from Spain and I get a kick out of the novelty.   

I find the study of propagation one of the most interesting aspects of radio. 



11 comments:

  1. Huh. So that's how I used to listen to BBC Gibraltar and Radio Free Europe in the evenings.

    ReplyDelete
    Replies
    1. Depends on the frequency. If you heard them on the 25 MHz Shortwave band or watched British TV, possibly. Watching British TV took work because they used a different broadcast system than the US; PAL vs. NTSC here. If it was lower in the shortwave spectrum or even the AM broadcast band, it was D or F layer propagation.

      Delete
    2. I picked up the NDB on Adak Island 51.87N 176.67E on the AM side of my truck radio. I was at 35.33N 121.06W on the CA coast. I identified the station by the continuous Morse ID.

      Rick

      Delete
    3. NDBs transmit on AM. This occurred just after evening twilight, I forget which month.

      Rick

      Delete
    4. Of course, I'm not familiar with those NDBs, but the Non Directional Beacons I know of are all below the bottom of the AM broadcast band. I've listened to a few just to prove to myself that I could do it on my surplus, 1960s-era R-390A.

      But because those are so low in frequency that was definitely not Sporadic E. I'm pretty sure that sort of propagation is either ground wave or D layer.

      Delete
  2. This brings back memories. When I was studying for my Novice license, back in the early 70's, my two teachers didn't just teach us enough to pass the test, but they actually taught us about electronics, radio theory, safety, both in radio-electronics and working at heights. We used ocilliscopes nearly every class session, and with signal generators and such as well. Much of this was not needed for our license, but was useful for us as new hams of that period. I do remember much of this propagation information, but of course, much has also passed me by, as I am going to be 60 this month. But please, keep on posting about this topic, when you can. It is very interesting and enlightening. And I am sure that many of the newest generation of hams have never seen this before. This recent sunspot cycle threatens to be another low one, and that can be a learning lesson for us all.
    pigpen51 KA8KRV, formerly WN8SZG, and WB8SZG

    ReplyDelete
    Replies
    1. Sounds like you had a really good class!

      I intend to go over other types of propagation, and more about prediction programs. There's lots to go over in the comments to the previous post.

      Delete
  3. One of the very few times I operated on 6 Meters I was treated to a massive Es opening. I had a full-size 5/8-wave vertical on the roof of the two story building I lived in back in SoCal, and my trusty Yaesu FT-847.

    I made dozens of contacts during the hour long opening, some as far away as Pennsylvania, and many in Iowa, Illinois, Missouri, Kansas, and Nebraska. Signals were consistently over S9, some going S9+30, and no fading. Just solid contacts every time I called CQ or answered someone.

    It was amazing, and made me understand why it's called "The Magic Band".

    There's a semi-local guy, K0GU, who's really big into 6 Meters. I see his callsign a lot in the "World Above 50MHz" column in QST.

    ReplyDelete
    Replies
    1. Back about '84, I homebrewed a 2 meter transverter to get on 2m Sideband. It took a couple of months and then I spent a couple of months with an indoor quad antenna on my workbench.

      After about six months, I finally got it raised into place (at 15') and got into the first Sporadic E opening on 2m I ever heard. Into Missouri and Kansas IIRC. I've only gotten a few states confirmed on 2m, though. Only a couple of days in 35 years that we got openings into Northern New York, Ontario, Canada and a few other places.

      On 6, I have all of the lower 48 states confirmed and I'd like to complete WAS without going to moon bounce or satellites, if possible. KH and KL are really hard from here without those.

      Delete
    2. One of my friends back in SoCal, Chip Angle, N6CA, has WAS and DXCC on 6 Meters. He had trouble with the New England states, but hit KH and KL with ease!

      And it took him years to get DXCC.

      Never got very far on 2 Meters, unless you count AO-7 and AO-10!

      Delete