Grantville Gazette, Volume 73

by Bjorn Hasseler

  There is, however, a poorly-supported theory that the Freemasons are, in fact, the descendants of members of the Templar order, who were forced to "go underground" after the order was betrayed and banned by the Church in the early fourteenth century. This theory began to gain popularity in the early- to mid-eighteenth century, and while romantic, it does not stand up to close scrutiny.

  Finally, the principles and beliefs of the Masonic fraternity are closely aligned with the Enlightenment—equality, fraternity, freedom of thought—and the modern-day society derives much of its true philosophy from the beliefs of that era; all of that precedes the seventeenth-century incarnation of Freemasonry. In short: whatever the form of the fraternity in the seventeenth century, it will be a lot different than the twentieth-century form. It will be secretive, charitable only within its membership, jealous of its privileges, and—unlike the up-time version—doctrinaire and likely hostile to "outsiders"—even people who know the modes of recognition. Up-time Freemasons will have a tough time cracking the shell of down-time ones.

  J. G. Findel's History of Freemasonry gives an account of the development of the Steinmetzen, a society of stonemasons in the Holy Roman Empire. Findel identifies the headquarters of the organization as Strasbourg, with subordinates—Bauhütten—which might compare with lodges, with the oldest ones in various cities in the Empire dating from the thirteenth century. He notes that there was some decline in the Bauhütten over the next two centuries, but in 1459 a confederation of nineteen Bauhütten formed a new confederation. They gathered in Ratisbon to write a set of Ordinances to govern it, and these statutes became the standard throughout the Empire, confirmed by a series of Emperors. These Steinmetzen—actual operative stonemasons—used recognition modes (Wahrzeichen) and initiation ceremonies that were similar to those used by Freemasons in modern times. The Thirty Years' War seriously disrupted the fraternal activities of the Steinmetzen, as well as putting many builders and craftsmen out of work.

  Understand, however, that the Steinmetzen in the Empire were operative Masons—they actually worked with tools and built things. They were bound together by more than fraternalism; they were professional colleagues.

  Interaction Between Up-time and Down-time Masons

  Properly treated, the interaction between up-time Freemasons and down-time Steinmetzen would be a good source of interesting stories. The Steinmetzen would by their nature be more secretive and more jealous of their relationships; any chance encounters would be the result of some accident, like an up-time Mason seeing a recognition sign or overhearing a password and then seeking to greet the down-timer. These are unlikely to be received well, at least at the outset. But if a trusting relationship could be established, it would give the Grantville Masons access to a wide network of intelligence and local knowledge.

  ****

  In "Marine Radio in the 1632 Universe" (Grantville Gazette 52) and "1636: Marine Radio in the Mediterranean" (Gazette 66) we explored the possibilities for communication across salt water. We also considered, briefly, a few overland paths of special interest to the Navy and commercial shipping interests.

  Here, we'll turn the focus to communication across land. As before, we'll concentrate on reliable Morse code message-handling at commercial speeds and not other radio services such as broadcasting or navigation.

  In the previous articles, there were certain routes of particular interest, for which we could calculate power requirements. It's much less certain where military units will operate in the coming land campaigns, so instead we'll estimate the distances achievable with the power levels and antennas most likely to be available. Where to apply those capabilities must be left to authors and their topographic maps.

  Due to the complexity of the subject, this will be a simplified treatment of some representative cases. It would be impossible in a brief article to give thorough coverage to the motley menagerie of physical effects by which a radio wave can propagate across land. Not only are there entire books on the subject, but a thorough engineering analysis of any communication route requires topographic maps, ground conductivity maps, and local atmospheric data which neither we nor our fictional characters have.

  Beyond those limitations, canon decrees a decades-long hiatus in the high frequency ionospheric skip by which hundred-watt ham stations in our own era are accustomed to reach halfway around the world. That leaves our down-time friends with a remaining menu of propagation modes for which there is little published performance data in the high frequency region. It's possible to extrapolate from the handbook charts, but the uncertainties will be larger, and some useful physical effects may be overlooked altogether.

  Fortunately, our purpose here is not to achieve the accuracy and certainty which professional communication systems engineers are called on to accomplish in the real world. That takes shelves of reference books, adequate time to collect and analyze field survey data, and years of experience. Our objective is to offer reasonable guidelines for plausibility in science fiction.

  What we can do, then, is examine the major workhorses among the many land propagation modes and run the numbers for some representative cases. Those results can suggest when our characters could plausibly get a message through, when they couldn't, and when communication could become marginal and intermittent.

  Overview, for the non-technically inclined reader

  Grantville Gazette readers and authors come from a wide variety of backgrounds. A few preliminary remarks may be helpful to orient those whose first language isn't tech talk.

  First, the folks who are faced with setting up radio communication, whether in the real world or in our fictional universe, have a variety of goals that revolve around what reliable range is achievable with what means and at what cost. The tradeoffs get tighter if the station must be mobile; limitations on equipment size, weight, and antenna height affect range. And, all of this is a moving target. The bounds of what is technically and economically feasible will expand, rapidly at times, as the electronics industry and the national economy mature.

  Second, radio waves can travel from place to place by several different physical mechanisms, called "propagation modes" in tech jargon. They often occur in combination along different parts of a single geographic path. Each mode has its own quirks. The details of how a signal becomes weaker as it travels further from the transmitter determine what range is possible using a particular frequency, transmitter power, antenna design, and station location. We'll examine three major propagation modes: ground wave, free space, and sky wave. We'll also look at diffraction and reflection. Whether to think of the latter two as separate modes is as much a matter of semantics as anything else. They're separate physical effects, but in practice they generally show up as part of a path that's otherwise free-space.

  Third, the variables that radio specialists juggle are station location, transmitter power, frequency, antenna design, the height of the antenna's supporting structure, and the surrounding terrain. Location can be a compromise between where the communication is actually needed, and where it's possible to get a signal out past terrain obstacles. Power and frequency both depend partly on the transmitter technology (tubes, electromechanical alternators, spark gaps).

  The very longest ranges occur with night-time sky wave, largely limited by our period's quiet sun to frequencies below 700 KHz (wavelengths greater than 428 meters). Consequently, maximum performance requires very tall and expensive antennas, and high power to overcome the strong natural noise at such low frequencies.

  Conversely, mobile operations favor the smaller antennas that go with higher frequencies, and operate mostly by ground wave and diffraction-boosted free space modes. Ground wave ranges decrease with increasing frequency, but not in a linear fashion. Free space ranges depend almost entirely on antenna height above surrounding terrain, and diffraction is governed by bend angle over terrain obstacles.

  Where we stand

  By 1636, Grantville's electronics industry is no longer strait-jacket
ed by the dwindling legacy of up-time parts. In the last year and a half, it has crossed the threshold of sustainability. It's now manufacturing all the components for a simple but practical tube-based radio communication station. Production is still limited, but growing all the time.

  The main focus here will be on the performance achievable with that equipment. However, we'll also touch on the fairly numerous fractional-watt "tuna can" transceivers made earlier from salvaged up-time transistors.

  Calculations will lean toward the conservative side. The criterion throughout is a reliable and predictable communication service for military and commercial needs, when conditions are at the unfavorable end of their natural range of variation. At other times, signals are likely to be stronger and easier to copy.

  Supporting technical information

  The Terminology section of the original article in the series "Marine Radio in the 1632 Universe" contains a good deal of background information, which readers may find helpful to review. Two of the definitions are ubiquitous in propagation and antenna calculations, and worth repeating here:

  Decibels or dB: A logarithmic way to express a power gain or loss ratio P2/P1

  G=10Log10(P2/P1)

  The dB form of expression is very convenient. Gains and losses expressed in logarithmic form can be added up algebraically, instead of multiplying very large and small numbers. Gains are positive, losses are negative. For example, an increase in power by a factor of 10 is +10 dB, while a decrease by a factor of 1000 is -30 dB.

  Absolute power levels can be expressed as dB relative to some stated reference level, such as one milliwatt or the thermodynamic noise floor of a reference antenna.

  dBm: decibels relative to 1 milliwatt

  1 W=+30 dBm

  Fixed versus mobile stations

  One very convenient way to classify radio stations and networks is by mobility.

  1636 is a little early for the industry to achieve the miniaturization and the high frequencies best suited to mobile-in-motion operation.

  In the context of 1636 logistics, a reasonable definition of a "mobile" land station is one that can be transported in any vehicle up to a horse-drawn heavy freight wagon or a river barge, and set up in the field in half a day or less. "Fixed" stations would be everything else.

  Mobility has a major impact on the practical size of a station's equipment and the amount of radio frequency power it can generate—and indirectly, on the frequency bands and propagation modes it can use most effectively. The lower the frequency, the longer the wavelength, and the larger an antenna must be if it is to deliver optimum results.

  There are degrees of mobility. For a wagon-mobile station, the height of a tall tree is a practical limit for an antenna structure, whether actual trees or guyed poles are used to support the antenna. Sustained operation at up to fifty watts would be reasonably manageable for this kind of station. Anything more than that would present some difficulties.

  Five watts and a wire antenna would be more reasonable for a station that must be transported in a mounted scout's saddle bags.

  A likely practical limit for a major fixed station in this period would be a single guyed tower 150 meters high, with steam or water power to run the transmitter. Depending on the transmitter technology and prime power source, a kilowatt or more would be possible.

  Signal types and technologies

  We can also classify communication stations according to the type of signal they can generate and receive. That, in turn, depends on the transmitter and receiver technology.

  Tubes, transistors, and electromechanical alternators generate a fairly pure continuous sine wave, a "CW" signal. This concentrates the power into the minimum bandwidth necessary to contain the on-off keying of a Morse code signal—on the order of 100 Hz wide. Since the amount of natural noise that gets through the receiver is proportional to the bandwidth of the receiving filter, a narrow signal helps in maximizing the signal-to-noise ratio.

  The CW signal has no modulation other than the keying. It must interact with a tube or transistor oscillator in the receiver to generate an audible tone. Again, this helps maximize the signal-to-noise ratio by not wasting power on a steady carrier wave that contains no information. On the other hand, it also means that Grantville-made components are required in the receiver as well as the transmitter.

  Large fixed CW stations would start to appear toward the end of 1635. They would grow over the next few years into the backbone of Europe's new communication infrastructure. Once that backbone is up and running, a mobile unit (or one station in a mobile net) would only need to set up where one of these big stations can hear it. From there, it could dispatch a message anywhere the net reaches. Think of the fixed stations as the late 1630s information superhighway.

  Spark stations could be built nearly anywhere in Europe using down-time skills and materials, and they could be built long before Grantville learns how to make tubes. Rick Boatright has suggested that enterprising down-timers will get busy bringing up local spark nets and relay arrangements as soon as the cheat sheets appear.

  Unfortunately, a spark transmitter's output is a train of poorly-shaped short bursts of radio frequency power that repeat at an audio rate. This results in a low average power output and poor frequency control, spreading its limited power across a wide bandwidth.

  Complementing the spark transmitter, a crystal set doesn't require Grantville's manufacturing facilities, either. It can receive the burst-modulated spark signal, but it has both wide bandwidth and no amplification. It lets a lot of atmospheric noise through, and it's not very sensitive.

  Consequently, spark stations make much less effective use of their power than CW stations. They're far from useless, but their effective range is nothing like that of CW stations of similar power consumption and antenna design. Worse, far fewer of them can operate in a given frequency band without mutual interference, because of their broad signals.

  Most of the calculations that follow will be for CW, which is much easier to describe mathematically as well as much more effective. We'll get to spark, though.

  Suitable frequency bands for land communication

  For a given communication need, the choice of band depends on a variety of considerations. For any propagation mode, some bands work better than others, or reach further than others, or require less power than others, or are easier to build equipment for than others.

  By 1636, we can expect a first-generation family of simple tubes that deliver reasonable efficiencies at frequencies up to perhaps 15 MHz, at power levels from under a watt to a few hundred watts. That isn't everything the communication services would like to have, but it's enough to accomplish quite a lot. It will be a couple more years before the industry can master the design, materials science, and manufacturing of the more complex and expensive tubes that will open up the higher frequencies.

  Electromechanical alternators top out at around 600 kHz, but can reach tens of kilowatts.

  On the other hand, 500 kHz is about as low in the spectrum as we can expect the early builders to construct full-size transmitting antennas, even at the largest fixed stations. A standard quarter-wave vertical antenna for that frequency requires a 150-meter tower centered on a radial-wire ground plane 300 meters across. (The radial wires need not impede farming or grazing if they're buried or elevated.) Such an antenna could be externally tuned down to 400 kHz or so and still perform fairly well.

  To get a feel for the size of this kind of structure at such a low frequency, look at this picture from the Wikipedia article on antennas: https://en.wikipedia.org/wiki/File:Sendemast_Hirschlanden.jpg. Even this example is slightly shortened from optimum height, with a small capacitive top hat.

  Below that frequency we'd have to accept the engineering and cost tradeoffs of shortened antennas, which are both more expensive and less efficient. This picture from the Wikipedia article on T antennas is probably at about the maximum height that could be built with wood lattice towers: https://en.wikipe
dia.org/wiki/File:Antenna_of_WOR-AM.jpg.

  Many low-frequency antennas are a lot more complicated and expensive than that. See this example: https://en.wikipedia.org/wiki/File:Grimetonmasterna.jpg. They're technically possible, of course, but not likely to happen this early.

  The cost and real estate of huge antennas isn't the only obstacle to the early use of the favorable propagation characteristics at low frequencies, either. The atmospheric noise rises very rapidly below 500 kHz, requiring much more power to be heard at the greatest potentially possible distances. It's doubtful that such super-powered transmitters would be feasible or affordable this early.

  Bottom line: in this period, the most useful frequencies lie between about 400 kHz and 15 MHz.

  Propagation modes

  Propagation across land often doesn't lend itself to straightforward rules and calculations, because land isn't a uniform medium. It's not flat, the ground conductivity varies from place to place, and some locations are covered by lakes and swamps instead of low-conductivity dirt and rock.

  Multipath effects are common. Signals can arrive at a receiver by multiple propagation modes, and along multiple terrain paths by the same propagation mode. They can add in phase, enhancing the signal strength by 3 to 6 dB, or add out of phase, causing deep cancellations of 20 dB or so. As the temperature and humidity distribution of the atmosphere changes, the arriving signals can drift in and out of phase, sometimes as rapidly as a couple of times a second.