First published in CQ Magazine June 1980, p. 44
A sacrilegious re-examination of current wave propagation theory and proposal of a new, more comprehensive and logical alternative. Noted Canadian contester VE3BMV dares to challenge traditional thinking. Donít be intimidated by the title; this is an eminently readable, fascinating, and thoroughly thought-provoking article. (K2EEK)
An Innovative Theory Based on Fiber Optic Analogy
BY YURI BLANAROVICH, VE3BMV (K3BU)
* Box 292, Don Mills, Ontario, M3C
Quite often new advances in technology and measuring equipment, given the right opportunity and timing, can produce some surprising results. In my case it was the opportunity to advance from wire and vertical antennas into rotatable antennas. Being interested in the mechanics of radio wave propagation, observing the various modes of propagation and trying to put two and two together, I was not always satisfied with available explanations in the literature. The matter was aggravated when I started to play with high performance antennas: the Razor Beam of my own design. The first version of Razor consisted of 3 Quad and 2 Yagi elements. The next version on a 62 foot boom consisted of 7 elements: Yagi reflector, Quad reflector, two Quad driven Log cell elements, Quad director, Yagi director and Yagi director. Two stacked antennas were used on the 15 meter band, the top being at 106 feet and the bottom at 51 feet or alternately at 37 feet above ground. The antennas exhibit a very clean and sharp pattern with back and side lobes being down about 50 dB from the main lobe. The antennas were designed experimentally on 144 MHz models. As far as I was able to tell, those antennas produced maximum obtainable gain per given boom length with excellent front-to-side and front-to-back lobes. (More information on those antennas will be given in future articles.)
Being a dedicated contester, the real test of the antennas came in the contest fire. The excellent CQ contests, presented exceptional opportunities to observe ionospheric propagation. With the Razor Beams - a telescope instead of field glasses - a number of things could be observed that normally would be unnoticed when using "ordinary" antennas. (They also helped to achieve excellent results from relatively ordinary country, Canada and produced two world records in the CQ WPX SSB and CW contests, even with the operator being relatively out of shape!)
The CQ contests allowed me to observe a number of anomalies and exceptions to present propagation theories by virtue of the great amateur population on the air at the same time all over the world. At least 5000 stations were active on the 15 m. band.
The stacked antenna system allowed me to observe various angles of radio wave propagation and revealed
some interesting facts. The deeper I got into my observations, the more I became convinced that the present theory of electromagnetic wave propagation telling us of signals bouncing between the ionosphere and the earth is not all consistent and perhaps not (100%) valid. More thinking and sorting out of ideas led to some interesting conclusions that I would like to present here. It is my hope that this article will stir up quite a bit of controversy and discussion, and that it will contribute to the clarification of the matter. I believe that we are faced with another great opportunity for Amateur Radio to demonstrate it's ability to contribute to the science of radio communications.
Presented here are observations that I was able to collect in the limited time available (it is, after all, only a hobby). Some of the findings are summarized here. More work must be done to collect more accurate, supportive evidence. In future articles I would like to elaborate more on some aspects of the subject with perhaps wider participation by other Amateur Radio operators world-wide.
The present radio wave propagation theory is based on the assumption that radio waves are propagated by reflections from a mirror-like ionosphere, returning to the earth's surface, bouncing off it back to the ionosphere and so on. Let's have a good look at this theory and where and how it started, and how valid it is. Lets call the present propagation theory "reflective", so we can refer to it easily.
Marconi, in 1901, made his first DX contact across the Atlantic accomplishing something that his theoretical friends considered impossible - spanning a great distance with low power. According to calculations it was impossible to achieve such communication by propagating the signal over that great distance because with distance the signal would get so weak, that it could not be detected. A different phenomenon was at work that would allow propagation of signals beyond the line of sight.
Heinrich Hertz had demonstrated that radio waves propagated in straight lines and found that their direction could be altered by reflective surfaces of conductive material. In 1902 it was suggested in two independent studies by Kennelly from the US and Heaviside from Great Britain that the upper atmosphere consisted of an electrically conducting region that deflected signals across the Atlantic. In 1924 the British scientist Appleton apparently discovered the electrified region and in 1925 he and his co-workers supposedly found conclusive evidence of its existence by measuring the angle of arrival of radio signals from a nearby transmitter. They figured that signals could only arrive from one direction - by reflection from the area in the earth's atmosphere about 100 miles high. For this work Appleton was Knighted by the British Empire.
In 1925 Briet and Tuve transmitted short bursts of radio energy vertically and detected echoes which they figured could be reflected only by the ionosphere.
Reflections are only one possible explanation for getting the signals from the sky at those angles. Too bad they did not get exposed to more work that was being done in optics at that time. In 1870 John Tyndall presented the earliest recorded scientific demonstration of a peculiar optical phenomenon - light being trapped in a stream of water. In his demonstration he used an illuminated vessel of water and showed that, when a stream of water was allowed to flow through a hole in the side of the vessel, light was conducted along the curved path of the stream. This was the closest thing to fiber optics. Lenses were already known. Too bad they did not see the similarity between radio waves and light, and get the idea of another way of propagating radio waves. Things had to wait. Today we know that light is on the high end or the electromagnetic wave scale.
So this was a handy explanation: "mirrors in the sky" reflecting radio waves back to earth; it was generally accepted. The idea has carried until the present. Any anomalies were judged as exceptions and all kinds of explanations have been tried in order to explain the mechanics of unusual propagation modes.
A Critical Look
Let's have a look at the reflective theory and see how well it fits real life. The first thing that really hit me is the scale to which all those nice pictures are drawn. It is immediately noticeable that the earth is usually drawn in one scale and the ionospheric layers are drawn in another scale, about 10x See fig. 1 showing the typical picture shown in the literature.
It explains how signals might reflect but it does not approximate the real geometric condition. Figure 2 shows the earth and the ionosphere drawn to scale. The average height of the F1 layer 'is around 180 km and the F2 layer about 500 km on a summer day. Assuming an average launch angle of 11 degrees on the 20 m. band, it seems that we need about four hops to propagate a signal one quarter way around the earth. Now if we work Europe on long path, we'd go about twelve hops. Considering the natural dispersion of the signal with distance and loss per reflection off the ionosphere and the earth, it seems to me that it is very unlikely that we could have any signal left at the other end.
Another questionable thing is the mechanics of the reflection from the ionosphere. Figure 3 shows the typical picture used in the literature explaining ionospheric reflection. In order to reflect signals one would expect a good reflective surface, larger in size than the wavelength and of good conductivity (reflectively) with clearly defined surface border. But we know that the ionosphere (atmosphere?) is very thin and molecules are far apart from each other. I find it hard to believe that we can get sufficient reflection of signals from that type of medium to yield the signal levels experiencing in Amateur Radio. The shape of the curve is also very unusual, it looks like refraction over about 270 degrees. In reality, the ionosphere would rather absorb the energy than "turn it around". So I am not very convinced that the mechanics of reflection are all that clear and acceptable.
Various propagation modes that cannot be explained by present theory are labeled as exemptions and there is great deal of speculation and explanation trying to find the place for them and make them fit the theory. For example, transequatorial v.h.f. propagation: signals bouncing off ionized bubbles; one way skip: investigation inconclusive; sidescatter, backscatter: bouncing a signal from an area of the earth which is reachable via the ionosphere from both ends of the path.
We will not elaborate too much on them; there is enough mentioned in the antenna and propagation books. We will try to explain these exemptions with a new theory.
The New Theory
One reason we are having problems understanding the mechanics of radio wave propagation is the fact that it is very difficult if not impossible to simulate the real situation in a laboratory set-up. We are dealing with sizable objects such as the earth, the atmosphere and number of variables that make the situation difficult to model here on earth. The best we could do is conduct some experiments using available means and perhaps complement them with studies done using satellites and electromagnetic wave sources here on earth or in space.
The closest analogy we understand and have available is optics and fiber optics. Radio waves and light have one thing common - they are electromagnetic waves with different wavelengths. Recent advances in fiber optics can help us understand the behavior of light propagation as well as radio waves. It is still difficult to find good analogy for the atmosphere because of its nature, there are great number of variables such as variance of height, density, pressure, dielectric constant, moisture content, temperature, chemical composition, charged particles as well as the effect of the earth's surface. The biggest contributor to ionospheric variations is radiation from space, mainly the sun.
When I started to look for a better, more satisfactory explanation of radio wave propagation it struck me that there must be more "conductivity" (refraction) going on up there than reflection. During my observations over the past six years I came to the conclusion that radio waves propagate in a medium that resembles a cloud or a cross between a cloud and fiber optics.
The basics of the new propagation theory can be summarized in the following statements:
A majority of the radio waves are refracted and propagated - conducted - along the borders of media with different dielectric constants and are accompanied by scintillation.
The geometry of propagation is dependent on the frequency used and the condition of the atmosphere.
The propagating medium has a cloud-like formation with the density and conductivity varying along its profile and dependent on the physical condition of the atmosphere and the amount of radiation from space.
It is quite difficult to accurately visualize the mechanics of the radio wave propagation. We are dealing with a three dimensional medium with varying density and a cone of radio signals propagating through that medium. The situation is also complicated when considering a broad spectrum of frequencies and different angles of refraction and conductivity dependent on the frequency.
In order to clarify the situation and to make it easier to understand we will make some simplifications. The beam of transmitted radio signal will be simplified and shown as a ray. We will use a solid line for relatively strong signal, broken line for medium strength and the dotted line for the weak signal. Density or radio-conductivity will be shown as a heavier shaded area for better conductivity and the lighter shading for worse conductivity.
Looking at figure 4 we have the earth and the atmosphere drawn to scale. The signal is transmitted from the point A. Signal strength decreases rapidly in the line of sight distance and we don't get much signal beyond point B. The main lobe of the antenna puts more signal into the space. Refraction begins at point C. A portion of the signal gets refracted, a portion goes through as shown at D. The refracted signal continues through the points E, G and H, more or less following the curvature of the layer and scintillating along the path. Scintillation is noticed and received as what we call backscatter or sidescatter signals. A portion of the signal is refracted along its path and received at the points W, X, Y, Z. Part of the signal continues through point D to F, where it either gets refracted or escapes into space at S. A portion of the signal from the higher path can be refracted back to earth at point K, at a different angle and combine with the signal propagated by the lower path causing considerable QSB. This is a simplified view of what is happening "up there." In a real life situation it gets a little bit more complicated due to the wider beam width of the transmitted signal, irregularities in the medium, and the range of frequencies and angles of the transmitted signal.
There is an indication that the speed of travel or propagation of the radio waves can vary in different layers and this combined with the scintillation or scattering of the signal, can be observed as Doppler shift of signal's frequency.
Scintillation in this case can be compared to the situation where we have a strong source of light with its beam going through the patch of fog or smoke. Particles of fog will be "glowing" or scintillating and become visible - detectable by our receivers - our eyes. Portion of the beam will continue to propagate after passing through the fog patch.
When observing the rising or setting of the sun and moon we observe refraction of light in the layers of the atmosphere. It is well known fact that sun or moon can be "seen" after they actually set below the horizon, the lag being about 12 minutes in time. Also the image or the size of the sun quite often appears to be larger than normal. This is definitely not reflection. We do not see the "mirror image" but the actual "picture." The same thing is happening when we travel along the highway during a hot summer day. Hot air above the road's surface causes the refraction of light rays and we can see the images of the objects that are actually slightly higher. (sky, fence, etc.) They are moved and blank out the background. The same is happening with 'Fata Morgana' (Mirage) in the desert.
Why should not radio waves behave in the similar manner? Light is electromagnetic wave with very short wavelength. The longer wavelengths are easier to refract or bend and harder to reflect.
During our "muscle flexing" with VE3HGN, who is about 70 miles East of my QTH, we have noticed an interesting phenomenon. While comparing antennas and during tests with overseas stations we found a shift in frequency on our signals when compared to the frequency of the DX station. First we thought that it was a flaw in my equipment (tuning), but repeated checks with DX stations confirmed that we were both dead-on the same frequency. But when listening to each other we were about 500 Hz lower in frequency. That could only mean that there is Doppler shift occurring somewhere. That, to my knowledge could be caused by a moving media or source, or perhaps different speeds of propagation being observed from the side. If there is a difference in the speed of propagation, it would mean that the signals are propagating in the layers by "conduction" (refraction, ducting) rather than reflection.
Another form of this effect can be observed when passing under the high tension power lines and listening to the car radio on the a.m. band. Depending on the location of the transmitting station and the direction of power lines, when passing under the wires a sudden frequency shift is observed, very similar to what we call selective fading. This can be explained by the different speed of propagation of the signal along the wires as opposed to the speed of propagation in the air. This "selective fading" is noticeable on h.f. and the frequency shift can be also observed on the s.s.b. signals coming from Europe. During contacts with OK2RZ on 15 m. I have observed QSB of his signal and at the same time slightly frequency shifting of his signal.
Familiar "Arctic Flutter" and raspy signals propagated from the Aurora are another example of the frequency shift caused by propagation of the signals through the medium. Arctic flutter can be simulated by tuning two receivers to the same signal and slightly detuning one receiver's v.f.o. The signal will sound as if it just passed over the pole, with familiar flutter. With the signals propagated through the auroral region, there is multiple frequency shift apparent, making s.s.b. signal reception almost impossible. Another noticeable feature of this frequency shift is the absence of the higher notes in the audio response of the shifted signals.
Known "Negative Doppler Effect" observed on the satellite signals can also be attributed to frequency shift caused by propagation.
Frequency shift has been observed to be present when experiments were carried out in both directions, east and west. It appears to be present at times on signals going across the Atlantic, but it is harder to detect due to the dominating "direct" signal. It is also more difficult to detect the shift on DX signals, because the shift will be more or less the same in both directions, therefore both stations will be "on the same frequency."
One important thing is apparent from this: when one is trying to calibrate his receiver to WWV, and his QTH is such that he is receiving a "backscatter" signal, then there is good chance that he might be off by about 500 Hz.
Let's assume for now that signals are propagated by conductivity rather than reflections and we will have a look at the various modes of propagation and see how well they fit the theory. More detailed descriptions, will be presented in subsequent articles.
Lets assume the simplified situation for the purpose of understanding the geometry of various modes of propagation. We will assume again that we have single ray of radio signal and simplified model of the atmosphere.
Figure 5 shows the average situation where signal is transmitted from point A and gradually bends, refracts through the atmosphere with a gradually changing dielectric constant reaching point D, placed on a more distinct border of two layers with different dielectric constants. The main portion of the signal follows the border along line D, E, G. A portion of the signal refracts back to the earth and allows us to receive the signals with relatively even strength along line W, X, Y, Z. Depending on the refractive angles we can receive signals under low or higher angles as shown along D-W and D-X. Point V gets almost no signal, because the angles of refraction will not supply any signal. Very weak signals can be observed at point V "seeing" scintillation at points E and G under low angles with low angle antennas. It appears that we are propagating the signals at considerably lower heights than previously thought. The dotted line shows the path A-M-W as explained by the reflective theory.
A portion of the signal transmitted from the point A is transmitted at a different angle and is refracted or partially refracted and reaches another layer or escapes into space as shown at A-C and A-C'.
Having antennas with low angle of radiation extends the useful range of propagation under adverse conditions with lower angles of refraction.
Day - Night Variations
Let's have a look at the typical path of a signal radiated at a 45 degree beam heading from VE3 over Europe to Asia, fig. 6.
The Sun is over Europe, it's morning in North America, and evening in Asia, The atmosphere is warmed by radiation from the sun raising the height of the layers and changing the dielectric constant of the media affecting the refractive angles. The hump over Europe causes the signal to change its direction - refraction - and this is experienced as a "black out" following noon local time in that area. Some weak signals are being heard, with the typical hollow sound. This is mainly the result of scintillation. It is very difficult to make the contacts from OK to other areas. VE and UA0 have no problems communicating, with conditions actually peaking at UA0 This is a changing situation with time of day, radiation from the sun, frequency, and angles of refraction. Shown example is typical for higher frequencies in the range of 14 - 30 MHz. There is a delay of about 2 hours (hysteresis) between the local noon and the "hump."
It is known that with increased sunspot activity the thickness of the atmosphere increases. (This caused Skylab to come down prematurely). This also increases the height of the propagating layers and therefore increases the height and length of the "arches", it allows us to span longer distances and extends propagation later into the night.
We have been told that during peaks of solar activity the lower frequency bands are very poor, mainly because of attenuation of the D layer of the ionosphere. On the contrary, the propagation on the low bands has been better than what we experienced during the sunspot minima. The 40m. band has longer openings to remote areas of the world. Eighty meters is the same; we are hearing Europeans around 6 p.m. local time. During the 160m. CQ Contest I was hearing G stations for about 8 hours during the night. It appears again that the refracting layers are higher, allowing us to work longer distances with stronger signal levels.
It appears then that with higher sunspot activity, the average height of the media increases, refraction of higher frequencies improves, allowing us to work further and increase the number of useful frequencies for communication.
We have no problem explaining long path propagation. It is just an extension of the short path propagation with the signals following the higher layers, where the losses can be lower and signals attenuated less. We still get the refraction towards the earth and the signals are heard along most of the path. See fig. 7. The path does not have to be in a straight line. Quite often we experience skewed path. The skewed path can be the result of side refraction which will produce quite strong signals, or caused by scintillation, characterized by low angle and weak signals.
The best case of long path would be the situation when signals get "trapped" in layers with low attenuation, and travel a number of times around the earth causing long delayed echoes. There is also the possibility that signals might enter Van Allen belts and propagate within the belts.
The best answers could be provided by satellites. Observation of the various satellite signals (on HF frequencies) will help to clarify a number of unanswered questions. Any room left in the space shuttle?
Gray Line Propagation
In the case of gray line propagation we have a situation where the medium is more or less at the same height, the refractive layers are more uniform, without major humps and therefore allow us to propagate signals along that path over quite wide range of frequencies with relatively small attenuation or refraction in the unwanted directions. Again the low angle antennas should perform best. When the signals are aimed in the direction of the grey line, just about any point on earth on the gray line can be communicated with, especially at the lower frequencies.
One Way Propagation
Quite often we experience a sort of one way propagation, i.e., on the 40m. band East Coast to Europe in the late afternoon. Strong signals from Europe are heard, but it is nearly impossible to work the Europeans. When switching between high and low angle antennas there is almost no difference. Later on, signals become stronger on the low angle antenna and contacts become possible.
This can be explained by scintillation, such as we can see on the end of a fiber optic fiber. When light exits the fiber and there are some impurities, it disperses the light at various angles. It is very difficult to enter the fiber under those conditions. A similar situation can exist with our radio signals and the conducting layers. Another form of one way propagation can be caused by different refractive indexes at both ends of the path. Going in the one direction signals can be refracted gradually and due to local conditions at the other end they can exit or be refracted towards the earth. For the transmitted signal the angle of refraction can be different and it will not refract the transmitted signal into the same layer that the received signal is coming over.
Trans-equatorial VHF Propagation
This type of propagation was discovered when stations located close to the same meridian were able to work each other, typically across the equator. Contacts were made between KP4 and LU. The world record on 2m. is between 5B4 and ZS. The propagation usually peaks just after sunset.
This appears to be another form of grey line propagation, where we have uniform medium with gradually hanging height around the equator, refracting signals over great distances. I would predict that given good conditions it might be possible to establish the contacts on the 2m. band between the VE and LU.
Various modes of v.h.f. propagation can be explained and understood better by applying the new theory. If refraction and scintillation are considered, then we can explain most of weird modes of v.h.f. propagation. Refraction then replaces reflection, and scintillation replaces scatter. It also appears as mentioned earlier, that signals are propagated (refracted) at lower heights then previously considered assuming reflection by the ionosphere. Horizontal polarization seems to be better for the long haul v.h.f. propagation probably due to the fact that the orientation of borders of the media with different dielectric constants are oriented horizontally, enhancing the refraction of horizontally polarized signals.
One of the very low frequency mysteries are the whistlers. They are bursts of signals in the range of 0 - 30 kHz, usually caused by the lightning strokes. They are "whistles" changing the frequency downwards and lasting from the fractions of the second to 10 seconds or so.
This can be also explained by our theory if we apply Doppler shift and multiple path refractions. Consider that lightning could start the whistler and propagation by refraction and variable speed will cause the frequency to change and change the time required to travel a given distance.
Receive vs. Transmit
Having different antennas available during contests and switching between low angle and higher angle antennas I have found during numerous tests that there is quite a difference between the angles of received and transmitted signals. This has been observed on bands from 10m. down to 80m. Also the optimum angles change from day to day, hour to hour. This is very important to know, especially for contesters, who cannot afford to wait in the pileups. Ideally the most successful station would have antenna systems capable of directing signal in the desired direction and at the most favorable angle too. The differences at times amount to around 20 dB. The stacked beams are worth gold!
Discrimination against noise is very important too. Quite often we can select the angle where signals would be about the same strength but the background noise from the band is considerably lower. S/N ratio improves tremendously.
Another thing that was found while switching between high and low angle antennas was the fact that most of the so called "short skip" (backscatter) signals are strongest at the low angle. Stacked beams were the best for working W l,2,3,4's on 15m. It made the difference of about 800 US contacts in the contest as compared to another station operating the same band and having a single antenna with higher angle of radiation. This also supports the refractive theory.
In cooperation with Amateur Radio operators around the world we can further explore and experiment with the propagation of radio signals. We can probably do it better and cheaper than a government or commercial effort. Hopefully we can reinforce the new theory and can open new possibilities and modes of propagation across the whole range of frequencies. Verification of the new theory will have great implications on antenna design, improved reliability of communications, and overall performance of radio stations. It will help to establish better methods of predicting radio wave propagation and develop more reliable means of forecasting propagation based on the factors known to affect it. Hopefully it will set the record straight and make more sense and fewer exceptions.
Hopefully this article will inspire hams as well as scientific institutions to more in-depth study and eventually produce operating formulas and diagrams, which, given the right set of values, will enable us to predict propagation with much better accuracy.
Amateur satellites with transponders on the lower frequency bands such as 160 to 80m., or 80 to 40m., or perhaps one utilizing the new 10 MHz band and having the elliptical orbit would be an ideal tools to explore the validity of the new theory.
Let's not be afraid to challenge a long-accepted theory.
What I have tried to present in this article is the expression of what I feel, what I have observed and what I think makes sense. I find it quite difficult to describe or express exactly what I am experiencing. This is partially due to the lack of good clean analogy, partially due to the difficulties of verification and expressing accurately what is happening up there. I hope that I succeed in getting the main message across: "Maybe there are no mirrors up there but more likely something like layers or clouds which can conduct (duct) or refract radio waves."
Much more work has be to done. This is just a brief outline of what I was able to gather in my limited available time.
Thanks to contests, I think I "see the light" a little brighter. Contests are moving force and inspiration for many advances in the field of Amateur Radio communications, so please put up with the contest racket when you hear it and if you can, give us a point or multiplier. This is the only reward for all the work we put into those super antennas and stations.
I would like to express my sincere thanks to my XYL Sonya for letting me "play with the radio", to Don, VE3HGN for his help with the experiments, to all those participating in the contests and experiments for their cooperation and valuable reports, and last but not least to CQ Magazine for providing the opportunity to publish the theory for the first time and for supporting the finest in Amateur Radio Contesting.
I hope to see you all in the next contest!