It would appear that we are on track for less than stellar radio conditions of the next few years.

73, Lee ZL2AL

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Your signals are effected by the Angle of Radiation as they travel from your radio to the other side of the planet. This paper by K2WH explains why.

Angle of Radiation – What is it?

One of the more important performance characteristics of an antenna system is its angle of radiation. Angle of radiation is not built into an antenna, you the amateur make that happen by the placing your antenna at the proper height. Therefore, I thought of this mental exercise of what radiation angle really means.

Angle of radiation when referring to antennas, is simply the take off angle of the RF field when launched from your antenna in relation to the ground (earth). That is, if your dipole antenna is low to the ground (< 1/2 wavelength), in relation to its frequency of operation, the angle of radiation from the dipole will be at or close to 90 degrees – straight up and the dipole will behave as an omni-directional antenna. The higher you place your antenna above ground, the lower the radiation angle. A height is finally reached (depending on installation), when the “Take off” angle (Magic Height) is in the 20 degree range or lower. A radiation angle of 20 degrees or lower is an ideal angle for working long range DX. This means, the major lobe of your RF energy is radiated at an angle of 20 degrees in relation to the horizon. The horizon being zero.

The “Magic” antenna height is generally achieved when your antenna is 1/2 wavelength above ground assuming a perfectly conducting ground (earth). There are many variations in ground conductivity ranging from something very similar to an insulator (sand and broken beer bottles) to salt water which is the best with everything else in between. Different ground types make the 1/2 wavelength rule different depending on where you live. If you live by the ocean, you are very lucky indeed. If you live in the mountains, you’re not so lucky.

How do you know when you are about 1/2 wavelength above your ground? Simple math. Take 468 and divide it by the frequency you intend to operate. Again assuming perfect ground, this number just happens to be the same number you would use to cut a resonant dipole to length.

This begs the question, “Why should I bother to achieve a low angle of radiation”. If you want the strongest signal possible at a distant point, a low angle of radiation is essential. 

For instance:

You want to put up a dipole antenna for 40 meters, frequency is 7.250 MHz. Therefore, 468 / 7.250 = 64.55 feet. This height will vary depending on your type of ground, but generally it is the approximate height you would want your feed point to be located for best DX capability. It will give you a low angle of radiation which is very good for working DX. Believe it or not, some angles of radiation are better than others for working different parts of the planet. That’s another story in itself. 

Visualize this:

Suppose I have a rubber ball in my hand. I throw it as straight down as possible at the floor. It will rebound and probably hit the ceiling directly above the point where it hit the floor. It will then hit the floor again and then rebound to hit the ceiling again close to the same spot again, all the while losing energy in the bouncing process from floor to ceiling. This will continue until all the energy is used up. Notice the ball did not travel very far from the origin point.

The floor in this example, can be looked upon as your ground, the ceiling the reflecting medium or, the ionosphere. This is how your signal travels from a low dipole delivering a very strong local signal because most of the RF energy is expended locally. The signal (ball) goes straight up and straight down for the most part. The result is many hops losing energy as it moves forward very little.

Now if I throw the same ball at the floor so it rebounds at about a 20 degree angle from the floor, the ball travels much further on the first bounce before it hits the ceiling. On the second bounce, it has moved quite far from its origin point. This is how your signal travels from a dipole when it is 1/2 wavelength above perfect ground. It travels much further between hops and loses much less energy before arriving at its final destination – the DX station. Remember however, your signal has now become directional so don’t point the ends of your high dipole to the part of the world you want to talk to. No free lunch here.

With a 20 degree take off angle, your local signal is much less powerful because most of the RF energy is passing overhead and not being reflected straight down. Local stations hear your ground wave signal which is good for about 50 miles and not very strong beyond that. You receive mediocre signal reports from your 1/2 wavelength high dipole vs your low dipole. This is why a vertical is considered a superior antenna for DX vs a dipole because they have an inherent low angle of radiation when installed properly and are not directional but usually require lots of radials to work properly.

Now if you are a DX hunter, a low angle of radiation is a good thing. A low angle of radiation equals a good DX antenna but if you want a strong signal locally, then a low dipole with a high angle of radiation is better.

As we can see, to really do your best with the DX and still have a good strong signal locally, you really need 2 antennas that you can switch between. You need one antenna with a high angle of radiation and one antenna with a low angle of radiation. Quite possibly, a low dipole and a good vertical.

I hope this helps readers out there to grasp the meaning of “Angle of Radiation”.

K2WH 

73, Lee ZL2AL

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All you need to know about old Sol and how he affects your quality radio time.

Solar Activity Primer

Propagation Primer 101

For those of you who seem hopelessly lost with all this solar and propagation stuff, I will attempt a quick primer that will help you understand what happens to your radio signals.

Quiet Sun at Sunspot Minimums

We all know the sun goes through a solar cycle about every 11 years. During the minimum, or QUIET SUN, there are few sunspots, the solar flux is very low (SFI is less than 100), which means the sun’s ionizing radiation is quite low. As a result, our upper atmosphere, where the E and F layers reside, are not well ionized. This means the E and F layers do not reflect HF radio waves very well … and most of your signals will pass right on through to space to be picked up by Jodie Foster in the sequel to “Contact.” One measure of how well ionized our E and F layers are is the MUF, or Maximum Usable Frequency. During the quiet sun, the MUF is often below 15 to 18MHz. This is why 15M and 10M are “dead” during the quiet sun, except for local (line-of-sight) communications.

High Sunspot Activity

However, during the solar maximum or ACTIVE SUN, there are many sunspots, the solar flux is high, and this highly ionizes our ionosphere. This in turn means our E and F layers become very reflective to HF signals. Virtually all the power hitting the E and F layers will be reflected back to Earth and little ends up in space. This high reflectivity causes the MUF to rise, often to above 30MHz. And when this occurs, 10M will be open all day long to support global communications by using “skip propagation” … in that your signals are skipping (or being reflected) off the ionosphere back to earth.

OK … now a couple of definitions:

Sunspot Cycles Since the 1940s

Current Cycle

SOLAR FLUX INDEX (SFI) is a number that attempts to describe the total power output of the sun at radio wavelengths, which in turn helps describe the total ionizing power delivered to our ionosphere. The higher the SF, the more ionization, and the more reflective our ionosphere is to HF.

An SFI of less than 100 is fairly poor propagation with the MUF less than 15MHz An SFI greater than 150 is fairly good propagation and the MUF will be over 25MHz

A general rule of the thumb is 10M is open when the solar flux is greater than 150.

IONIZATION. The solar radiation reaching the Earth contains IONIZING radiation. This means the incoming solar radiation can rip electrons away from the oxygen molecules high in our atmosphere. So now you have all these “free electrons” roaming around that makes the upper atmosphere (or ionosphere) more dense. Now the mass or weight doesn’t change, it’s just denser. Think of a bunch of popcorn balls on a floor, and shooting a marble through the open spaces without hitting a popcorn ball. Likely, not hard to do. The marble represents your radio signal passing through to space.

Now go out there and stomp those popcorn balls so a bunch of individual popcorn kernels are scattered all over the floor. The mass of the popcorn has not changed, but it is distributed to make the field more dense. Now try to shoot that marble across the floor without touching a piece of popcorn. Going to be very hard to do. The marble, or your RF signal, does NOT pass on to space. In the real case, your RF signal strikes all these free electrons, and that is what reflects them back to earth … DURING DAYLIGHT HOURS when ionization occurs.

A really amazing thing happens to our ionosphere when the ionizing radiation from the sun goes away (night time), The free electrons rejoin or recombine with their host molecules, making intact oxygen molecules again. In our example, this would be like watching all the popcorn kernels on the floor magically turning back into popcorn balls again. Of course, this means RF signals will again pass through on to space and will not be reflected.

Interestingly, when electrons are stripped away from oxygen, it turns the oxygen molecules into helium. Another way of measuring the extent of ionization is to measure the amount of helium in our upper atmosphere. This is usually done through optical spectral line equipment or launching high altitude instrument balloons. However, this is seldom done today since other means and satellite surveillance is far more superior for measuring the extent of ionization.

This is why the higher bands, such as 15M and 10M, are open with signals being reflected back to earth during the DAYLIGHT HOURS. These same bands go dead (no reflective propagation) nearly as soon as the sun sets – because the sun’s ionizing radiation goes away.

This is also why these same bands tend to be completely dead during the quiet sun, because there is insufficient ionizing radiation to cause ionization for reflection. This is a phenomenon of the active sun, the period we are well into right now. And, during a quiet sun, the ionization can be so low, that the MUF drops below 14MHz at night, which is why even 20M can go dead at night. During an active sun, the MUF almost always remains above 15MHz even at night, which is why 20M often becomes a ’round-the-clock band during the active sun.

So what about 40M and 80M? The solar cycle has virtually no effect on 40M or below. Propagation on 40M, 80M and 160M remains pretty much the same during the active sun as it does the quiet sun, because the MUF seldom drops below 10MHz. This is why 40M is the main night time band, year in and year out. Even with low ionization, the very long wavelengths of the lower frequencies will be reflected by the ionosphere. This would be like rolling a basketball through the popcorn balls … while the high frequency RF (the marbles) pass through pretty easy, certainly the low frequencies (basketball) would not. Quiet sun or active sun.

The active sun DOES effect 40M in that absorption to RF can be very good to very bad, or very high noise levels from geomagnetic storms … both due to solar flare activity that occurs only during an active sun. A large solar flare sends an extra dose of ionizing radiation to the Earth. This can raise the MUF to very high frequencies (greater than 100 MHz), but this radiation can also penetrate far into our atmosphere to ionize the lower D-layer. RF signals must pass through the D-layer on their way to the upper E and F layers, where the reflection occurs. The more ionized the D-layer is, the more collisions that will take place with your RF signal, absorbing or attenuating some of its power. Thus, high absorption to HF signals can occur during and after a solar flare. This would be like rolling that marble across the popcorn covered floor, which encounters so many collisions with the popcorn that the marble comes to a halt. Now that is total attenuation or absorption. Your poor little QRP signals just vanish on their way to the E and F layers!

80M signals are almost always highly or fully attenuated by the D-layer, and what “propagation” that occurs on 80M is actually by the signals traveling across the Earth’s surface, or “ground wave” propagation. The wave front is confined between the Earth’s surface and the D-layer, which causes attenuation to the power as it travels along the ground, skims the D-layer, and propagates through the dense atmosphere near the surface. This is why QRP on 80M is challenging at best since the absorption rates are fairly high – day and night, quiet sun or active.

The other major effect to HF propagation during the active sun is geomagnetic storms. Very briefly, this is caused by a shock wave from a solar flare hitting the Earth’s magnetic field, causing it to compress and wiggle for awhile. And while it’s wiggling, it’s generating huge electrical currents, which in turn creates gobs of noise on HF. I’ll present geomagnetic storms in another lesson.

SUMMARY:

    BAND         THE QUIET SUN                    THE ACTIVE SUN
….80M…. Seldom has skip propagation…..Seldom has skip propagation
….40M…. Open around the clock……………..Open around the clock
….30M…. Open daylight hours………………….Open around the clock
….20M…. Open daylight hours………………….Open around the clock (usually)
….15M…. Dead – no skip propagation……….Open – daylight hours only
….10M…. Dead – no skip propagation……….Open – daylight hours only
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73, Lee ZL2AL