Radio FAQ Part 3

RF Environment

From a radio specialist's perspective, Eric Flint could not have chosen a worse time to drop a town into than 1632. Just at the beginning of the period where there are telescopic observations of the heavens, approximately simultaneous with the trial of Galileo, 1632 drops Grantville into the beginning of a time best known as the "Maunder Minimum. "

At about the same time as Galileo published his description of his construction of the Dutch invention of the telescope, natural philosophers throughout Europe began noting that the sun had imperfections, "spots" on it. This was far easier to watch with a lens, since you could project an image of the sun onto a white sheet, and observe it without destroying your eyes, and the novelty led several natural philosophers to begin a regular program of noting the sunspots on a daily basis. Therefore, we have an excellent record of the number of sunspots starting in about 1600,

This notion of the imperfection of the sun would have come as no great surprise to the court astronomers of China and Korea. In the court logs of the observations of those staff astronomers there are sunspot records made with the naked eye going back another thousand years. Using those records, we can trace the sunspot number from about 600 AD, using a reasonable relationship between the capabilities of naked-eye astronomers and those using projections and lenses.

For all of this 1300-year period of recorded observations, the number of sunspots on the surface of the sun has varied in an 11-year cycle. As of this writing, in late 2002, we are near the falling side of the peak of the current cycle with sunspots near the historic high of over 200. This extreme activity has resulted in spectacular auroras begin seen as far south as 30 degrees north (Oklahoma city) at the other end of the measure, the lows have had sunspot numbers in the low teens to the mid 20's The "average" low is between 20 and 30.

For reasons that no one at all understands, starting in about 1610, the number of sunspots plummeted. By 1632, which should have been a peak year, the sunspots where down to the mid-teens, and by 1640, had dropped to zero. The 11-year cycle did continue, with peaks as high as 8 or 9 between 1640 and 1700. The, for reasons that no one understands, starting in 1710, the numbers went back up, and have continued, quite regularly for the last three hundred years. This is _not_ a "lack of observations" artifact, the court observations in china and Korea, and the western records correlate quite well. This is real.

Recent work by observational astronomers using a combination of new techniques and really really smart people on type G3 stars like our sun have figured out a way to measure the sunspot number of a star even though we can not "image" the star. This work indicates that G3 stars may typically spend as much as 20% of their time in this "quiescent" mode. It could start again tomorrow. No one has any models for why it happens, or what causes it or why it stopped. It's all quite confusing.

So what you say? Well, it turns out that the number of sunspots is very highly correlated with the thickness of the upper layers of the ionosphere. There are several "layers" in the upper atmosphere, which get ionized for different reasons. These are labeled from the outside in A through F.

The innermost F,E, and D layers are caused each day by the action of the ultraviolet light on the earth's upper atmosphere. This is the same action that splits O2 apart and gets the free oxygen that can combine into the O3, to form the "ozone" layer. These ionization layers form every morning at sunrise, and thicken throughout the day, and then begin to fade at sunset The combination of their chemistry, and their electrical properties cause them to absorb radio waves longer than about 4MHz. That's why, during the day you can only hear your local AM radio station, but at night, you can pick up the one from the other side of the country.

Shorter wavelengths pass right through the DEF layers.

Further out, the ABC layers are ionized not by UV light, but by the action of the solar wind on the outer layers of the earth's atmosphere and its interaction with the earth's magnetic fields. During periods when there are lots of sunspots, the sub puts out a lot of particles, and these ionization layers are quite thick and robust. Without the solar action, during sunspot minima, the ABC layers are thinner and weaker, the thicker and more robust the outer layers are, the shorter the wavelength they can refract or reflect. During sunspot maxima, the maximum usable frequency, (The MUF can get as high as 30 or even 50 MHz. (six meters) That is, 30 MHz signals can bounce right off the ionosphere, or be trapped between two upper layers, and ducted around the world before breaking out and coming down most anywhere. That's how CB radio "skip" works, when folks listening to the radio in their cars on the highway in Kansas, here the chat between boats working the shrimps in the gulf of Mexico. Normally a CB radio is good for 5 miles, but when the sunspots are out, all bets are off.

Even during a normal sunspot minimum, when the sunspot count is down around 20 or 30, the MUF stays up around 14 MHz (20 Meters) for at least part of the day, and seldom goes below 7 MHz (40 Meters)

The higher the MUF, the shorter the wavelength and the smaller the antenna that is needed. In General, we want to use as short a wavelength as we can, not for any "macho" reason, but because the higher the frequency, the smaller the antenna we have to build. A six-meter transmitter uses a "natural" antenna that is only 1.5 meters long. But a 40-meter transmitter uses a natural antenna that is 10 meters long. Thus, the higher the MUF, the more convenient it is to build radio installations. Most hams therefore, work the 20-meter bands, and the 40-meter bands are not uncommon. But it's the rare ham that works 80 or 160 meters, since the natural antenna for 80 meters is 20 meters long, and 40 meters long for 160 meters...

However, remember the sunspot story from way up at the top of this post? During the Maunder minimum, during the period that Eric has set 163x in the middle of, the ABC layers of the ionosphere _go away_ to a great extent. Of course, there is always SOME solar wind, and there will be SOME ionization and SOME reflection, but the MUF keeps dropping and dropping till by 1640, to do long-distance communications without relays, you need to be using 2 MHz for much of the day, and can get up to 4 MHz only late at night. '

And remember that the DEF layers ABSORB the long waves, so the low MUF means that you have little if any ability to do long distance communication during the day at all.

So, the radio installations in 163x end up using very very large antennas. The most common antenna for a diplomatic mission will be installed this way.

Take a piece of wire, 40 meters long and cut it in the middle, Put a glass insulator in the center of it, and hook anther piece of wire to each of those 20 meter long pieces, the "hookup" wires are held apart every few inches by a hunk of glass or plastic or wood, like a little ladder 2 inches wide. This ladder leads back to the transmitter. Meanwhile, take your center insulator and haul it up to the top of a tower as high as you can get. 150 feet is really a good height. Attach the glass insulator to the tower, and then, draw a line on the ground, in the direction of the city you want to talk to the most. Stretch out each of the 20 meter long legs, out away from the tower at 60 degrees up from vertical (30 degrees down from horizontal) perpendicular to the line you drew (crossing it) hook the end of each wire to a rope with another glass insulator, and pull the ropes taught so that the wire is as straight as you can get it.

Now, remember how you drew a line towards the radio you want to reach, that you want to "beam" at? Build another tower, 20 feet back away from your destination, on that line. Now, do the exact same thing with another piece of wire on that tower. (You do not need hookup wires on this one)

So, two 150-foot towers, two 40-meter long hunks of wire, suspended in the air, and lots of rope. If you want to use 1.7 MHz, (160 meters) instead of the 3.5 MHz we designed this for, double all the numbers above (well, you can keep the tower height the same, but taller is better)

Repeat this, as often as necessary to build a beam pointing at each city you want to talk to. A big central diplomatic radio installation will have a cluster of these beams pointing in a variety of directions and will require a clear level space a quarter of a mile on a side...

As we approach 1640, the electronic situation in the atmosphere worsens, and the MUF drops towards 1.7 MHz, and the antennas and such get bigger as above, and harder to build. It's not fun. That's why Gayle and Jeff kept muttering about the bad timing of the radio situation in 1632 and 1633. From the perspective of a Ham, you where dropped straight into hell.

What do you do about it? Well, you do several things. 1) You use a lot of power to overcome the fact that not much bounces 2) you experiment to find the best frequencies available and use them 3) you build good antennas. 4) You send your messages at the right time of day (generally a window about 4 hours starting at sunset called the "gray line") 5) you set up relays, you send the message as far as you can, and then relay it. Thus, the team in Amsterdam relays to London and to Scotland. Similarly, the diplomatic and commercial team in Venice will relay to Rome, and to Istanbul (Loops, sorry, Constantinople.) 6) You maximize the use of the power you have, by using CW (Morse code) instead of voice, Voice requires far far far far far better signals than CW does.

But that's the situation until we can get satellites back up, which will be 50 to 100 years. Which is about the same time that the short-wave bands re-open in 1700. Long distance radio will be a very very very different thing than we experienced in our timeline, and as tube production comes on line, and high power radios go into production around the world, bandwidth for long distance communications will be a precious and rare resource. The pressure to build cables across the ocean will be even higher in the 163x universe than it is in ours.