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Plasma Physics for the Radio Amateur, III

Created by Eric Nichols, KL7AJ on 2010-04-30

Plasma Physics for the Radio Amateur

Part III

Radio would be a lot simpler if the Earth was flat. Actually, a lot of things would be simpler if the Earth was flat. In fact, if you look back in history, to when the Earth actually was flat, it's pretty clear that life was a lot simpler for all involved.

Alas, Christopher Columbus and his henchmen had to really mess things up, especially for us radio amateurs. The biggest problem with Mr. Columbus' invention of a round Earth is that radio waves are still flat. Mr. Columbus, in one glaring oversight, totally failed to take this into account. Five hundred years later, we are left to deal with the fallout of Mr. Columbus' ill-conceived adventure.

To be perfectly accurate, radio waves aren't really flat, but they do travel in straight lines unless they find a truly compelling reason to do otherwise. The fact that there are radio amateurs on the wrong side of a round Earth is not generally a compelling enough reason, in and of itself, for radio waves to make the effort.

Lacking additional incentive, the farthest a radio wave will travel is to the horizon, another unfortunate side-effect of Mr. Columbus' "new and improved" round Earth. For a neck-height wire antenna, the horizon is about nine miles. In reality, the "radio horizon" is about 30% farther than the visible horizon. We usually use the "4/3 Earth" rule-of-thumb for radio horizon distance. Calculate the geometrical horizon using an Earth that's 4/3 as big as its actual diameter, and you come pretty close. Now, if you have two radio amateurs on opposite sides of the radio horizon with neck-height antennas, you can actually communicate a little under 18 miles; not quite as grim a picture, but certainly nothing to write home about.

Now, it's no big mystery that the higher you go the farther the horizon is. If you want to talk farther you just raise your antennas above neck height. That's the good news. The really bad news is how quickly you reach the point of diminishing returns by making your antennas higher. The radio horizon only increases as the square root of the antenna height. Look at it like this. Going from moose-neck height to giraffe-neck height gains you a lot. Going from giraffe-neck height to Empire State Building height gains you almost nothing!

What, oh what is a round-Earth bound ham to do, other than to have no friends more than 18 miles away?

There are actually two main approaches to this problem. The first is to use the round-Earth itself to bend the radio waves. There is actually sort of an ironic poetic justice in this method. It's really "sticking it to The Man," The Man being, of course, Christopher Columbus.

So far, all our previous discussion of radio wave propagation has involved propagation through a vacuum, or through air, which, as far as radio is concerned, is about the same thing.

Radio waves traveling through, or in contact with, something other than free space, behave differently. When a radio wave travels through a solid material like dirt, it slows down a little bit. (It also loses some energy due to heating loss, but we can ignore that for now). The important thing to know is that a radio wave passing through dirt moves a little more slowly than a radio wave passing through air. This is not too hard to grasp.

But, what happens if part of a radio wave travels through dirt, and part of it travels through air? Things get very interesting. The best way I know of to demonstrate this is with a Slinky. I trust you have a Slinky lying around someplace. Even one of those abominable plastic ones will work.

Now, if you were to lay the Slinky down on a flat surface and stretch it out a bit, the outline of that Slinky will be a perfect sine wave. (This is the geometric projection of a helix onto a plane, for you geometry whizzes). Now, let's pinch the bottom of the coil together, so each lower wave peak is slightly closer together than the upper wave peaks. What does the Slinky do? It bends toward the closer-together peaks. It has no choice, unless you allow the Slinky to break. Radio waves must be continuous-nature will not allow you to have a broken radio wave. The radio wave must bend toward the "slower" direction portion of itself. Voila, a curved radio wave!

This curved radio wave in contact with the Earth's surface is called a "ground wave," for pretty obvious reasons. Now, ground waves are really only practical for lower radio frequencies, such as the A.M. broadcast band and lower. The heat losses we mentioned a few paragraphs back increase with increasing frequency. Above a couple of megahertz, ground waves do little more than heat up the dirt. But at lower frequencies, they are the dominant mode for worldwide radio communications. And they REALLY work great when the Earth is made of sea water.

Take THAT, Mr. Columbus!

In fact, ground wave (or sea-surface) propagation for many decades was the primary means of over-the-horizon radio communications. 500 KC was the international maritime distress frequency until very recently, having served its purpose well for about 100 years. (It was the frequency used on the Titanic. The fact that nobody heeded the radioman's warning has nothing to do with the effectiveness of the radios or the propagation). I've talked to a few old time radio officers, and they say that 500 kc was like an international party line of telegraph operators-nearly 100% reliable communications over most of the earth.

The main problem with communications at low frequencies, at least as far as hams are concerned, is that antennas are necessarily large. The lowest frequency Amateur Band is 160 meters, which is really at the upper edge of where ground wave communications are possible. A good deal of your efforts to make a 160 meter ground wave antenna will serve little but to heat up earthworms.

Fortunately, there's another approach to over-the-horizon communications, which is actually the primary means for most long-distance amateur radio communications. We can bounce signals off the ionosphere. Actually, bouncing isn't a very accurate description; it's a bending process much like our groundwave.

The ionosphere is much like many of the other spheres that circle the Earth, such as the Atmosphere, Troposphere, Mesosphere, and such. They're all-well-spherical. Sort of.

Which makes one wonder what people called the atmosphere back before Columbus, when the Earth was flat. The Atmosflat?

In any case, the Earth is surrounded by varying gases of different densities and pressures. The vast, vast, vast majority of these gas molecules are neutrals. They have no electrical charge, and have no effect on radio signals, whatsoever. Remember our chapter, Electrons: The Tools of the Trade? We said that in all things electronic, it's really the electrons that do all the work. And they really can't do much if they're tied to molecules or atoms, other than keep the molecules or atoms company. Neutral gases are pretty invisible to radio waves; there's really nothing in them to even respond to radio waves.

Starting at an altitude of about 90 kilometers, however, a tiny number of these atoms can get their electrons slapped off their carcasses, which then become free electrons. Or at least, fairly cheap ones. The main electron-slapping ingredient is ultraviolet radiation from the sun, and you don't have to be a rocket scientist to conclude that probably much more electron-slapping happens during the day than at night.

Precisely how many of these electrons get slapped off their host atoms determines how much stuff we have to bounce radio signals off of. Now a whole lot of interesting things happen when electron-slapping happens, all of which falls into the field of plasma physics.

Although I worked in the field for many years, I'll avoid the temptation to deliver a course on plasma physics in this chapter. You can get a much more entertaining introduction to that branch of science by reading my novel, Plasma Dreams. (Shameless commercial plug here).

One of the interesting things that happen is that these slap-happy electrons tend to organize in layers of sorts, and begin to exhibit collective behavior, must like your local Teamsters Union. Except they never ask for overtime. That's why they're called free electrons.

Now, the atoms that get their electrons slapped off them are called ions. Ions also exhibit a collective behavior, which is why we call that collection of ions the ionosphere. These ions don't generally affect radio signals directly, but they do give a certain sense of direction to the free electrons. Without the remaining ions, the free electrons would flail off in every direction, because they are, being like-charged, mutually repelled.

Perhaps you're asking why the ions don't go wandering off merrily as well, since they also are now mutually repulsive. Well they do, but very slowly. Even though they have the same magnitude of charge as their off-slapped electrons, they have thousands of times the mass! So, though the ions will gradually drift apart (diffuse), in most regards act mechanically like any other gas. In fact, you actually have weather-like phenomena happening in the ionosphere, just like in the atmosphere. Well not just like, but you do have recognizable patterns of movement and such way up there.

So, the end result is, we have this big sluggish ionosphere keeping free electrons on a very long leash. The result of all this couldn't work better for radio propagation if it was intentionally planned. (Actually, I'm one of those folks who sincerely believe the ionosphere was specifically created for bouncing radio signals off of. Just like believing that trees were created as antenna supports. But that's just me).

Now, there's an interesting little item called the electron density profile. It's sort of a perverted bell curve sort of thing lying on its side. You can see this as a black line on many ionograms available online. (I use the HAARP ionosonde, which shows conditions valid for most of Alaska. (www.haarp.alaska.edu) You can find a nearby ionosonde by looking at the Lowell Digisonde site map.)

What the electron density profile shows you is the relative number of free electrons at any altitude from about fifty kilometers to about six hundred kilometers. This is the best indication of how good the sky is going to be at reflecting radio signals at any particular time. Now, why the funny curve, and not just a straight line? Good question. We actually have two conflicting things happening.

Since air pressure is highest at ground level, and decreases as we go up, there are more atoms available to get their electrons slapped off of. So the lower we go, the greater potential for the creation of free electrons. But-and it's a big but-the ultraviolet light has to travel farther though absorptive air to get to those high density atoms. So while there are more atoms to ionize at lower altitudes, it is easier to ionize them at higher altitudes. The breakeven point is usually at around 250 km altitude or so, the normal peak of the "bell curve". It is generally around here where you will find the most number of free electrons milling about. There's also usually a smaller peak at around 100 km or so.

Now, we haven't really explained how an electron reflects a radio signal, though we've described how these electrons congregate. Actually, you CAN reflect a radio signal off a single electron, and there are scientific devices called incoherent scatter radars which do just that, but this is pretty science-geeky stuff. As radio amateurs, we're much more interested in reflecting radio signals off mobs of electrons.

If we have a decent, well-behaved ionosphere, we have more or less a sheet of electrons, which in some ways, acts a bit like a sheet of copper. We have a region of sky that is highly electrically conductive. Unlike a wire, it's conductive in all directions, north-east-west, and south, not just along a line. We also have some conductivity up and down, because our electron sheet can be many kilometers thick. Oh, I must also clarify one point here. Please do not get the impression that we have any significant volume of sky that consists of nothing but electrons, any more than we have any volume containing nothing but ions. Any region of the ionosphere we look at will have all three items: electrons, neutrals, and ions occupying the region in varying concentrations. High free-electron content just means there are a lot more free electrons at that height than at other heights.

Well, back to our conductive sheet analogy. The electrons are free to accelerate in any direction in response to a radio wave impinging on them. They will line up and slosh back and forth in accordance with the electrical part of the wave passing through their midst. But what do sloshing electrons do? Why, they create radio waves! This is why we were emphatic about the reciprocity theorem in the antenna chapter. It doesn't matter whether you're a slosher or a sloshee. One creates the other, and the other creates the one. (Important reminder: Remember, it's acceleration of electrons that creates electromagnetic fields, not their mere movement. This is a crucial distinction. The acceleration can be linear or angular, though for free electrons, it's usually linear acceleration we're most concerned about).

This is also why I was reluctant to describe the ionosphere as reflecting radio waves. It actually absorbs and re-radiates them. Looking at what happens from the vantage point of your station on the ground, this may seem to be a minor point of semantics, but it makes a big difference when we look at the more peculiar aspects of ionospheric or "skywave" radio.

Now, if all those nice slap-happy free electrons happened to coagulate in a nice spherical shell at about 250 kilometers, all around the round Earth, life would be wonderful all the time. Worldwide skywave communications would be possible anywhere at any time.

But alas, there are several flies in the ointment.First, many of our electrons do find their ways back to the ions from which they were slapped. Well, not the exact same ions, but ions from the same ion mob.

Recombination takes place, and our ions become neutrals, of no value for radio propagation. This recombination is relatively slow, which is why shortwave radio propagation doesn't suddenly quit the instant the sun goes down. In fact, a good number of electrons never do recombine, which is why you still have skywave propagation at night, at least on the lower H.F. frequencies.

Secondly, we have ionospheric weather. Remember, our ions are basically floating on top of the atmosphere. As tenuous as the connection is, genuine weather effects down here on the surface do eventually transfer to the ionosphere. It's certainly not a one-to-one correspondence, but there are storms and currents and other weather-like disturbances that all do one thing-they upset the nice calm layers of electrons we need for decent "reflection" to take place. Instead of a "mirror" we have a wall of rocks.

Sooner or later most hams will experience a sudden "blackout" of radio communications, also quite common on the lower frequency bands, during the evening when you're basically using those "leftover" un-recombined electrons. This is seldom if ever due to a sudden, spontaneous recombination, where gillions of electrons miraculously find their way back home to their family ions. No, these sudden outages are frequently caused by electron precipitation-all the electrons are quite literally being sucked down a hole in the bottom of the ionosphere, traveling down the Earth's magnetic field lines into the Earth's surface, where they are dissipated.

Electron precipitation events can be triggered by almost anything: a distant lightning strike, a burst of cosmic energy, auroral activity, or just sheer statistics.

The ionosphere is inherently unstable; it's much like trying to float water on top of oil. It can be done if you're really really really really really really really really really really careful. But the slightest disturbance will cause the liquids to suddenly change places, putting the water on the bottom where it belongs. In a similar fashion, there's only one place an electron wants to be (other than an atom from which it got slapped), and that's sliding down a magnetic field. Magnetic fields are irresistible water slides for electrons. The fact that a stable ionosphere can exist at all with the Earth having a magnetic field is nothing short of astonishing. The fact that radio works at all in Alaska, where the North magnetic field is concentrated, is astonishment on steroids.

Let's Get Critical

Probably the most useful information the radio amateur can get from the electron density profile is the critical height.

Let's illustrate this point with a little test setup. Let's build a transmitter and receiver, and put a super high gain antenna on each, so we can place them right next to each other without interference. We'll aim our transmitter and receiver antennas straight up into the ionosphere. While we transmit on one antenna, we listen for the ionosphere reflected signal with the other antenna. We actually do something similar to this in what is called NVIS (Near Vertical Incident Skywave) communications, a very reliable H.F. military mode.

If you shoot a radio signal straight up into the ionosphere, whilst listening for reflections, constantly increasing the frequency as you do so, there will be some frequency at which you get no signal reflected back at all. The frequency at which this happens is called the critical frequency, and the height at which this all happens is the critical height. Both of these are very useful for calculating radio propagation, but let's look at critical height first.

Critical height, interestingly enough, always corresponds with the maximum electron density! In other words, you can never get any reflections from anything higher than the maximum electron density point. This is a good thing to know.

Sometimes, critical height is called "the height of the ionosphere." This is not precisely true, but it's a useful enough misapprehension. A little simple geometry will show you that having a high ionosphere is better than a low one, when you're trying to bounce a signal beyond the horizon. Now, it's certainly possible to use multiple bounces when transmitting beyond the horizon, and indeed this is exceedingly common in amateur radio communications. But generally, it's best to get the job done with as few skips as possible, for at least two reasons. Number one, there are losses associated with every ionospheric bounce, so the fewer of them you need, the stronger your signal will be. Secondly, the prediction of multi-bounce skywave radio assumes the ionosphere at the other guy's end of the chain is the same as it is where you are, a very "iffy" assumption, indeed.

At any rate, the critical height is a good quick and dirty means of calculating how far you can get on your first bounce.

Now, critical frequency, on the other hand, has a lot more information to offer. And it also requires a much better understanding of the ionosphere. When thinking about critical frequency, we need to toss out our "mirror" analogy of the ionosphere, and replace it with a "prism" analogy. Remember when we said our "electron sheet" is very thick? A reflection from a thin layer, like the silver coating on a mirror, gives us something called a "specular" reflection. Radio reflections from the ionosphere are anything but specular, except for some really notable exceptions, which is why they're called "notable exceptions."

Most of us are familiar with a standard optical prism. You place this wedge of glass in sunlight, and it spits out all the colors of the rainbow, each one "bent" at a different angle. Well the ionosphere is very similar; different frequencies are bent at different angles. The net result is similar to a prism, but the internal workings are quite different.

The ionosphere's prism-like character results from the fact that the critical electron layer (or layers) are not only very thick relative to the wavelength of radio signals penetrating them, but they are of continuously varying density. We say that the ionosphere has a continuously variable velocity factor.

Remember our bent Slinky experiment? In that case, we were only dealing with two "velocity factors," that of air, and that of dirt. In the ionosphere, we have a continuously varying velocity factor with height, but also one that varies with frequency! The physics is exceedingly complex, but the intermediate results are fairly easy to visualize. The crux of the matter is that higher frequencies penetrate the ionosphere farther before being "bent" than lower frequencies. What this means is that the "height of the ionosphere" is dependent on frequency.

Now, things just begin to get interesting.

For about a century there has been a conspiracy of silence in amateur circles about a couple of things known as X-mode and O-mode propagation. This is really surprising since X-mode and O-mode propagation modes have been known about for at least sixty years, and are fully acknowledged by just about every communications professional.

Here's the scoop. If you transmit a radio signal through the ionosphere, unless you happen to be at precisely the magnetic equator, (which is about as likely as finding a politician who can utter a truthful statement), your radio signal splits into two signals. One of these signals will be clockwise circular polarized.

This is known as O-mode (for ORDINARY mode, in the northern hemisphere). The other signal will be counterclockwise circular polarized. This is known as the X-mode signal (for eXTRAORDINARY mode, in the northern hemisphere.

(Yeah, I know, physicists can't spell, but at least it's memorable). At any rate, even if your transmitted signal is perfectly linear, such as generated by a simple dipole, by the time the signal gets up to the ionosphere and back down again, you have two signals, one spinning clockwise and one spinning counterclockwise. Now the plasma physics that creates this phenomenon is quite fascinating, but well beyond the scope of this course. The thing you need to know is that you will ALWAYS have an X-mode and an O-mode signal when you transmit through the ionosphere. This is so easy to prove with simple circularly polarized antennas that nobody has ever bothered to dispute it. But, true to form, most hams generally just ignore the whole topic and chalk up weird propagation to "black magic."

The fact of the matter is that a good deal of the "weirdness" of H.F. radio propagation can be explained by exploring the X and O properties of the signals. Probably 99.9% of all radio amateurs are clueless about this very fundamental property of the ionosphere. You can't blame the hams though, because it's totally absent in the amateur literature as well. We intend to fix that.

The correct thing to do is to TAKE ADVANTAGE OF THESE DIFFERENT MODES! The X-mode and O-mode signals not only have two different paths in the azimuth, but also have different critical heights. This is the sort of thing that ordinary hams can experiment with and actually make a contribution to the technology and science.

Take a look at a typical ionogram right here: http://digisonde.haystack.edu/latestFrames.htm. I've chosen the Massachusetts Digisonde, just so you don't think this whole X and O thing is an Alaskan aberration. Notice the well defined red and green traces? The red trace is your O-mode signal, and the green trace is your X mode signal. These are real time signals. The only difference is the polarization of the receive antenna. See how the green trace has a higher critical frequency AND critical height? This is real stuff, kiddies; not science fiction.

In a following chapter on practical antennas, we're going to describe some very simple circular polarized H.F. antennas, which you will not find in any other amateur radio literature! Consider yourself privileged.

KB1NLW2010-05-12
Plasma Dreams
Please put your novel, Plasma Dreams on Kindle

KB1NLW
Reply to a comment by : WA2JJH on 2010-05-08

Oh, yes there is that experiment too. Funny how the U.S. no longer makes the newx on partical physic s breakthroughs. Every topomax, collider. or smasher seems to have moved to europe. One could say that proves the 12 relms of reality hypothesis. (sic joke) One Physics honch I know from NYC is convinced we will be producing all our power needs from safe self refueling fusionn reactor. Pretty much a sun in a very large magnetic bottle jar. Hard to believe our sun as all stars are just a continuing ever exploding H bomb. If it was not for the earths complex atmosphere and powerfull magnetic fields......we would be toast. What was te latest perdiction, we got another 4 million years before enough hydrogen gets fused to helium, then our sun starts its beginning or should say ending of the red drawf stage. Our sun is too small to turn into a black hole. THE earth still has another 8 million years of life left. Of course an asteroid with just a few miles of diameter will knock earth off its axis first. lef
Reply to a comment by : KL7AJ on 2010-05-05

JH: My attention has been more focused on the National Ignition Facility. We may have a Star in a Jar by June, if things go according to schedule. :) Eric
Reply to a comment by : WA2JJH on 2010-05-03

Again ERIC........"GRReeattt stuff." Lots of things I used to know, should have known to more percise, and stuff I simply did not know. (or had a crappy idea). Yup, Maximum height is a concept that I needed a refresher course in. I remember we had to use 800W on C cand (3-6 gig) saturate our transpnder. Heck with Ku bands huge gain with small dishes, 10W and new MPEG like modulation works. C band needed a 30 foot dish on TX. Remember everbodys 10 foot dish for rxING C BAND. m.U.F, I used to follow when younger. Be nice the the new cycle is arriving. Be cool to work japan on 10M soon. Of course, I know micromaves were best for penetrating the ionosphere. Take make a satelite hop, KU band and even higher above 30 gig is good. Or Mil use's lots miliimeter wave freqs too. Quasi-optical effects affect antenna design. Funny how anything above 24 gig is a millimeter band, As you know, the 2 gig microwave ovens name would make on think the output of a magnetron is higher in frequency then those DRO's and injection locked amps. Have to admit, I never though we could generate watts at 100 gigahertz. Geesh that is onlt 2 octives away from the far infrared band. Thanks agn for some thought provoking. As for spelling and grammar here......I win the prize every year, ask anyone :) Enginneers and physist got better things to do!!!! Are you keeping up with the Stockhold super collider experiments this summer? They are smashing antiparticals around. Not just positon particals but anti-matter of hydrogen. Well it could be 12/12/12 sooner!
Reply to a comment by : NZ5L on 2010-05-01

What do you know - you CAN teach an old dog new tricks (arf, arf). Fascinating stuff, indeed! And I must agree, whole-heartedly, that the ionosphere was put there so that humans of the 20th century onward could use it for communication purposes. Likewise, oil was put in the the ground millions of years ago so we would have something to put in our gas tanks today. Superb advance planning! However, I don't know about the belief that deer have white tails to make them easier to shoot.
Reply to a comment by : K0DCH on 2010-04-30

An excellent article. It is absolutely astounding that radio waves propagate at all. Without the ionosphere things would be very grim. I worked on a project (about 30 years ago) to reconstitute a working ionosphere after a nuclear war. (I guess the electrons had all run for cover.) The plan was to launch torpedoes from surviving submarines which would then deploy balloons to carry reflecting material up to ionosphere altitudes.
WA2JJH2010-05-08
RE: Plasma Physics for the Radio Amateur, III
Oh, yes there is that experiment too. Funny how the U.S. no longer makes the newx on partical physic s breakthroughs.

Every topomax, collider. or smasher seems to have moved to europe. One could say that proves the 12 relms of reality hypothesis. (sic joke)

One Physics honch I know from NYC is convinced we will be producing all our power needs from safe self refueling fusionn reactor.
Pretty much a sun in a very large magnetic bottle jar.

Hard to believe our sun as all stars are just a continuing ever exploding H bomb.
If it was not for the earths complex atmosphere and powerfull magnetic fields......we would be toast.

What was te latest perdiction, we got another 4 million years before enough hydrogen gets fused to helium, then our sun starts its beginning or should say ending of the red drawf stage.
Our sun is too small to turn into a black hole.
THE earth still has another 8 million years of life left. Of course an asteroid with just a few miles of diameter will knock earth off its axis first.

lef
Reply to a comment by : KL7AJ on 2010-05-05

JH: My attention has been more focused on the National Ignition Facility. We may have a Star in a Jar by June, if things go according to schedule. :) Eric
Reply to a comment by : WA2JJH on 2010-05-03

Again ERIC........"GRReeattt stuff." Lots of things I used to know, should have known to more percise, and stuff I simply did not know. (or had a crappy idea). Yup, Maximum height is a concept that I needed a refresher course in. I remember we had to use 800W on C cand (3-6 gig) saturate our transpnder. Heck with Ku bands huge gain with small dishes, 10W and new MPEG like modulation works. C band needed a 30 foot dish on TX. Remember everbodys 10 foot dish for rxING C BAND. m.U.F, I used to follow when younger. Be nice the the new cycle is arriving. Be cool to work japan on 10M soon. Of course, I know micromaves were best for penetrating the ionosphere. Take make a satelite hop, KU band and even higher above 30 gig is good. Or Mil use's lots miliimeter wave freqs too. Quasi-optical effects affect antenna design. Funny how anything above 24 gig is a millimeter band, As you know, the 2 gig microwave ovens name would make on think the output of a magnetron is higher in frequency then those DRO's and injection locked amps. Have to admit, I never though we could generate watts at 100 gigahertz. Geesh that is onlt 2 octives away from the far infrared band. Thanks agn for some thought provoking. As for spelling and grammar here......I win the prize every year, ask anyone :) Enginneers and physist got better things to do!!!! Are you keeping up with the Stockhold super collider experiments this summer? They are smashing antiparticals around. Not just positon particals but anti-matter of hydrogen. Well it could be 12/12/12 sooner!
Reply to a comment by : NZ5L on 2010-05-01

What do you know - you CAN teach an old dog new tricks (arf, arf). Fascinating stuff, indeed! And I must agree, whole-heartedly, that the ionosphere was put there so that humans of the 20th century onward could use it for communication purposes. Likewise, oil was put in the the ground millions of years ago so we would have something to put in our gas tanks today. Superb advance planning! However, I don't know about the belief that deer have white tails to make them easier to shoot.
Reply to a comment by : K0DCH on 2010-04-30

An excellent article. It is absolutely astounding that radio waves propagate at all. Without the ionosphere things would be very grim. I worked on a project (about 30 years ago) to reconstitute a working ionosphere after a nuclear war. (I guess the electrons had all run for cover.) The plan was to launch torpedoes from surviving submarines which would then deploy balloons to carry reflecting material up to ionosphere altitudes.
KL7AJ2010-05-05
RE: Plasma Physics for the Radio Amateur, III
JH:

My attention has been more focused on the National Ignition Facility. We may have a Star in a Jar by June, if things go according to schedule. :)

Eric
Reply to a comment by : WA2JJH on 2010-05-03

Again ERIC........"GRReeattt stuff." Lots of things I used to know, should have known to more percise, and stuff I simply did not know. (or had a crappy idea). Yup, Maximum height is a concept that I needed a refresher course in. I remember we had to use 800W on C cand (3-6 gig) saturate our transpnder. Heck with Ku bands huge gain with small dishes, 10W and new MPEG like modulation works. C band needed a 30 foot dish on TX. Remember everbodys 10 foot dish for rxING C BAND. m.U.F, I used to follow when younger. Be nice the the new cycle is arriving. Be cool to work japan on 10M soon. Of course, I know micromaves were best for penetrating the ionosphere. Take make a satelite hop, KU band and even higher above 30 gig is good. Or Mil use's lots miliimeter wave freqs too. Quasi-optical effects affect antenna design. Funny how anything above 24 gig is a millimeter band, As you know, the 2 gig microwave ovens name would make on think the output of a magnetron is higher in frequency then those DRO's and injection locked amps. Have to admit, I never though we could generate watts at 100 gigahertz. Geesh that is onlt 2 octives away from the far infrared band. Thanks agn for some thought provoking. As for spelling and grammar here......I win the prize every year, ask anyone :) Enginneers and physist got better things to do!!!! Are you keeping up with the Stockhold super collider experiments this summer? They are smashing antiparticals around. Not just positon particals but anti-matter of hydrogen. Well it could be 12/12/12 sooner!
Reply to a comment by : NZ5L on 2010-05-01

What do you know - you CAN teach an old dog new tricks (arf, arf). Fascinating stuff, indeed! And I must agree, whole-heartedly, that the ionosphere was put there so that humans of the 20th century onward could use it for communication purposes. Likewise, oil was put in the the ground millions of years ago so we would have something to put in our gas tanks today. Superb advance planning! However, I don't know about the belief that deer have white tails to make them easier to shoot.
Reply to a comment by : K0DCH on 2010-04-30

An excellent article. It is absolutely astounding that radio waves propagate at all. Without the ionosphere things would be very grim. I worked on a project (about 30 years ago) to reconstitute a working ionosphere after a nuclear war. (I guess the electrons had all run for cover.) The plan was to launch torpedoes from surviving submarines which would then deploy balloons to carry reflecting material up to ionosphere altitudes.
KI4GSV2010-05-05
RE: Plasma Physics for the Radio Amateur, III
Great job explaining the MAGIC of radio. I can't wait for the next installment.

73,Fair Winds

Bill
Reply to a comment by : WA2JJH on 2010-05-03

Again ERIC........"GRReeattt stuff." Lots of things I used to know, should have known to more percise, and stuff I simply did not know. (or had a crappy idea). Yup, Maximum height is a concept that I needed a refresher course in. I remember we had to use 800W on C cand (3-6 gig) saturate our transpnder. Heck with Ku bands huge gain with small dishes, 10W and new MPEG like modulation works. C band needed a 30 foot dish on TX. Remember everbodys 10 foot dish for rxING C BAND. m.U.F, I used to follow when younger. Be nice the the new cycle is arriving. Be cool to work japan on 10M soon. Of course, I know micromaves were best for penetrating the ionosphere. Take make a satelite hop, KU band and even higher above 30 gig is good. Or Mil use's lots miliimeter wave freqs too. Quasi-optical effects affect antenna design. Funny how anything above 24 gig is a millimeter band, As you know, the 2 gig microwave ovens name would make on think the output of a magnetron is higher in frequency then those DRO's and injection locked amps. Have to admit, I never though we could generate watts at 100 gigahertz. Geesh that is onlt 2 octives away from the far infrared band. Thanks agn for some thought provoking. As for spelling and grammar here......I win the prize every year, ask anyone :) Enginneers and physist got better things to do!!!! Are you keeping up with the Stockhold super collider experiments this summer? They are smashing antiparticals around. Not just positon particals but anti-matter of hydrogen. Well it could be 12/12/12 sooner!
Reply to a comment by : NZ5L on 2010-05-01

What do you know - you CAN teach an old dog new tricks (arf, arf). Fascinating stuff, indeed! And I must agree, whole-heartedly, that the ionosphere was put there so that humans of the 20th century onward could use it for communication purposes. Likewise, oil was put in the the ground millions of years ago so we would have something to put in our gas tanks today. Superb advance planning! However, I don't know about the belief that deer have white tails to make them easier to shoot.
Reply to a comment by : K0DCH on 2010-04-30

An excellent article. It is absolutely astounding that radio waves propagate at all. Without the ionosphere things would be very grim. I worked on a project (about 30 years ago) to reconstitute a working ionosphere after a nuclear war. (I guess the electrons had all run for cover.) The plan was to launch torpedoes from surviving submarines which would then deploy balloons to carry reflecting material up to ionosphere altitudes.
WA2JJH2010-05-03
RE: Plasma Physics for the Radio Amateur, III
Again ERIC........"GRReeattt stuff." Lots of things I used to know, should have known to more percise, and stuff I simply did not know. (or had a crappy idea).

Yup, Maximum height is a concept that I needed a refresher course in. I remember we had to use 800W on C cand (3-6 gig) saturate our transpnder. Heck with Ku bands huge gain with small dishes, 10W and new MPEG like modulation works. C band needed a 30 foot dish on TX. Remember everbodys 10 foot dish for rxING C BAND.
m.U.F, I used to follow when younger.
Be nice the the new cycle is arriving. Be cool to work japan on 10M soon.

Of course, I know micromaves were best for penetrating the ionosphere. Take make a satelite hop, KU band and even higher above 30 gig is good. Or Mil use's lots miliimeter wave freqs too. Quasi-optical effects affect antenna design.

Funny how anything above 24 gig is a millimeter band, As you know, the 2 gig microwave ovens name would make on think the output of a magnetron is higher in frequency then those DRO's and injection locked amps.
Have to admit, I never though we could generate watts at 100 gigahertz. Geesh that is onlt 2 octives away from the far infrared band.

Thanks agn for some thought provoking. As for spelling and grammar here......I win the prize every year, ask anyone :)
Enginneers and physist got better things to do!!!!
Are you keeping up with the Stockhold super collider experiments this summer?
They are smashing antiparticals around. Not just positon particals but anti-matter of hydrogen.
Well it could be 12/12/12 sooner!











Reply to a comment by : NZ5L on 2010-05-01

What do you know - you CAN teach an old dog new tricks (arf, arf). Fascinating stuff, indeed! And I must agree, whole-heartedly, that the ionosphere was put there so that humans of the 20th century onward could use it for communication purposes. Likewise, oil was put in the the ground millions of years ago so we would have something to put in our gas tanks today. Superb advance planning! However, I don't know about the belief that deer have white tails to make them easier to shoot.
Reply to a comment by : K0DCH on 2010-04-30

An excellent article. It is absolutely astounding that radio waves propagate at all. Without the ionosphere things would be very grim. I worked on a project (about 30 years ago) to reconstitute a working ionosphere after a nuclear war. (I guess the electrons had all run for cover.) The plan was to launch torpedoes from surviving submarines which would then deploy balloons to carry reflecting material up to ionosphere altitudes.
NZ5L2010-05-01
RE: Plasma Physics for the Radio Amateur, III
What do you know - you CAN teach an old dog new tricks (arf, arf). Fascinating stuff, indeed! And I must agree, whole-heartedly, that the ionosphere was put there so that humans of the 20th century onward could use it for communication purposes. Likewise, oil was put in the the ground millions of years ago so we would have something to put in our gas tanks today. Superb advance planning! However, I don't know about the belief that deer have white tails to make them easier to shoot.
Reply to a comment by : K0DCH on 2010-04-30

An excellent article. It is absolutely astounding that radio waves propagate at all. Without the ionosphere things would be very grim. I worked on a project (about 30 years ago) to reconstitute a working ionosphere after a nuclear war. (I guess the electrons had all run for cover.) The plan was to launch torpedoes from surviving submarines which would then deploy balloons to carry reflecting material up to ionosphere altitudes.
K0DCH2010-04-30
Plasma Physics for the Radio Amateur, III
An excellent article. It is absolutely astounding that radio waves propagate at all. Without the ionosphere things would be very grim.

I worked on a project (about 30 years ago) to reconstitute a working ionosphere after a nuclear war. (I guess the electrons had all run for cover.) The plan was to launch torpedoes from surviving submarines which would then deploy balloons to carry reflecting material up to ionosphere altitudes.
KL7AJ2010-04-30
RE: Plasma Physics for the Radio Amateur, III
At HIPAS Observatory, we generally used inverted vees on thirty foot push-up poles. Made for easily deployable antennas. Since these actually consisted of two inverted vees at right angles, it also served as the guy wires! Very slick.

Once you have your inverted vees erected, you need to feed them 90 degrees apart. Just be sure the transmission lines are 90 electrical degrees different in length. You can feed these two dipoles with a simple T connector. To switch between X and O mode, you only need to change the polarity of ONE of the dipoles. Or you can have a 90 degree phasing line coiled up in the shack, which you can swap between the two feedlines.

eric

Reply to a comment by : WR9H on 2010-04-30

Thanks Eric and another great post. This is a great way to see what's going on up there. Now, how do I build the antennas needed for 40 meter X and O reception?? 73 Herb/WR9H
Reply to a comment by : KL7AJ on 2010-04-30

And this one from the Czech republic showing the same thing...LOTS of reflections! http://147.231.47.3/latestFrames.htm
Reply to a comment by : KL7AJ on 2010-04-30

http://www.iap-kborn.de/fileadmin/user_upload/MAIN-abteilung/radar/Radars/Ionosonde/Plots/LATEST.PNG Wow! Look at this one from Germany! FIVE very distinct reflections. This means VERY low absorption. Great DX conditions! Eric
Reply to a comment by : KL7AJ on 2010-04-30

Here is a list of the online Digisondes available. Some require a password; you can register as a visitor in most cases. http://ulcar.uml.edu/stationlist.html
WR9H2010-04-30
RE: Plasma Physics for the Radio Amateur, III
Thanks Eric and another great post.
This is a great way to see what's going on up there.
Now, how do I build the antennas needed for 40 meter X and O reception??
73
Herb/WR9H
Reply to a comment by : KL7AJ on 2010-04-30

And this one from the Czech republic showing the same thing...LOTS of reflections! http://147.231.47.3/latestFrames.htm
Reply to a comment by : KL7AJ on 2010-04-30

http://www.iap-kborn.de/fileadmin/user_upload/MAIN-abteilung/radar/Radars/Ionosonde/Plots/LATEST.PNG Wow! Look at this one from Germany! FIVE very distinct reflections. This means VERY low absorption. Great DX conditions! Eric
Reply to a comment by : KL7AJ on 2010-04-30

Here is a list of the online Digisondes available. Some require a password; you can register as a visitor in most cases. http://ulcar.uml.edu/stationlist.html
KL7AJ2010-04-30
RE: Plasma Physics for the Radio Amateur, III
And this one from the Czech republic showing the same thing...LOTS of reflections!

http://147.231.47.3/latestFrames.htm
Reply to a comment by : KL7AJ on 2010-04-30

http://www.iap-kborn.de/fileadmin/user_upload/MAIN-abteilung/radar/Radars/Ionosonde/Plots/LATEST.PNG Wow! Look at this one from Germany! FIVE very distinct reflections. This means VERY low absorption. Great DX conditions! Eric
Reply to a comment by : KL7AJ on 2010-04-30

Here is a list of the online Digisondes available. Some require a password; you can register as a visitor in most cases. http://ulcar.uml.edu/stationlist.html
KL7AJ2010-04-30
RE: Plasma Physics for the Radio Amateur, III
http://www.iap-kborn.de/fileadmin/user_upload/MAIN-abteilung/radar/Radars/Ionosonde/Plots/LATEST.PNG


Wow! Look at this one from Germany! FIVE very distinct reflections. This means VERY low absorption. Great DX conditions!

Eric
Reply to a comment by : KL7AJ on 2010-04-30

Here is a list of the online Digisondes available. Some require a password; you can register as a visitor in most cases. http://ulcar.uml.edu/stationlist.html
KL7AJ2010-04-30
Plasma Physics for the Radio Amateur, III
Here is a list of the online Digisondes available. Some require a password; you can register as a visitor in most cases.


http://ulcar.uml.edu/stationlist.html
KL7AJ2010-04-30
RE: Plasma Physics for the Radio Amateur, III
OOOH! I see some nics sporadic E action right now. See the flat section of the traces down at around 90 km


Eric
Reply to a comment by : KL7AJ on 2010-04-30

YF: Alas, the Haystack Observatory does seem to be out of commission, presently. Try this site: http://137.229.36.30/cgi-bin/digisonde/latest.cgi
Reply to a comment by : K5YF on 2010-04-30

Thanks for sharing this series of articles Eric!!!! I couldn't get the Haystack digisonde link to respond, so here is one that might have what Eric intended us to see. World Ionogram (updated every 30 seconds): http://car.uml.edu/WatchIt/latestIonogram.html ..but you will have to get Eric to explain what you are seeing on this graph and what it means to your radio signals....
KL7AJ2010-04-30
RE: Plasma Physics for the Radio Amateur, III
YF:

Alas, the Haystack Observatory does seem to be out of commission, presently.

Try this site:

http://137.229.36.30/cgi-bin/digisonde/latest.cgi
Reply to a comment by : K5YF on 2010-04-30

Thanks for sharing this series of articles Eric!!!! I couldn't get the Haystack digisonde link to respond, so here is one that might have what Eric intended us to see. World Ionogram (updated every 30 seconds): http://car.uml.edu/WatchIt/latestIonogram.html ..but you will have to get Eric to explain what you are seeing on this graph and what it means to your radio signals....
K5YF2010-04-30
RE: Plasma Physics for the Radio Amateur, III
the link I just posted shows data from a different observation station every 30 seconds... just let it refresh....

http://car.uml.edu/WatchIt/latestIonogram.html
Reply to a comment by : K5YF on 2010-04-30

Thanks for sharing this series of articles Eric!!!! I couldn't get the Haystack digisonde link to respond, so here is one that might have what Eric intended us to see. World Ionogram (updated every 30 seconds): http://car.uml.edu/WatchIt/latestIonogram.html ..but you will have to get Eric to explain what you are seeing on this graph and what it means to your radio signals....
K5YF2010-04-30
Plasma Physics for the Radio Amateur, III
Thanks for sharing this series of articles Eric!!!!

I couldn't get the Haystack digisonde link to respond, so here is one that might have what Eric intended us to see.

World Ionogram (updated every 30 seconds):
http://car.uml.edu/WatchIt/latestIonogram.html

..but you will have to get Eric to explain what you are seeing on this graph and what it means to your radio signals....
K6BSO2010-04-30
Plasma Physics for the Radio Amateur, III
Wait, wait--the earth is not flat? When did this happen? Why didn't I get the memo...
VO1FZ2010-04-30
RE: Plasma Physics for the Radio Amateur, III
That's it - he's a script-teaser!
Reply to a comment by : N5TGL on 2010-04-30

Argh! Such a tease. You are absolutely correct, there is just about a complete absence of X and O mode information. I know, because I've been looking! Sure am glad to see some coming out here. Can't wait for the next article. Michael
N5TGL2010-04-30
Plasma Physics for the Radio Amateur, III
Argh! Such a tease.

You are absolutely correct, there is just about a complete absence of X and O mode information. I know, because I've been looking! Sure am glad to see some coming out here. Can't wait for the next article.

Michael
N0YXB2010-04-30
RE: Plasma Physics for the Radio Amateur, III
Me too. I was just wondering yesterday when we'd get to see the next part of the series. Thanks for these great articles.
Reply to a comment by : VO1FZ on 2010-04-30

Again, fascinating is the word. Keep bringing it - I'm actually looking for your posts these days. eHam must be happy!
Reply to a comment by : K4KRW on 2010-04-30

Eric, What a way to start the day. Thanks for another fascinating article. (At the end of this series, who do I contact for my diploma?) 73, Richard K4KRW
VO1FZ2010-04-30
RE: Plasma Physics for the Radio Amateur, III
Again, fascinating is the word. Keep bringing it - I'm actually looking for your posts these days. eHam must be happy!
Reply to a comment by : K4KRW on 2010-04-30

Eric, What a way to start the day. Thanks for another fascinating article. (At the end of this series, who do I contact for my diploma?) 73, Richard K4KRW
K4KRW2010-04-30
Plasma Physics for the Radio Amateur, III
Eric,

What a way to start the day. Thanks for another fascinating article.

(At the end of this series, who do I contact for my diploma?)

73,

Richard
K4KRW