November/December 2000 QEX

68 Pages·2001·5.19 MB·English

About the Cover
N4UAU’s remote receiver
INCLUDING: from Part 2 of his series.
Part 3 adds a keyer and
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Issue No 203
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Features
Doug Smith, KF6DX
Editor
Robert Schetgen, KU7G
Managing Editor 3 On the SSW Path and 160-Meter Propagation
Lori Weinberg By Robert R. Brown, NM7M
Assistant Editor
Peter Bertini, K1ZJH
Zack Lau, W1VT 10 The Quad Antenna Revisited, Pt 3: Multi-Element
Douglas Page
Quads
Contributing Editors
Production Department By R. P. Haviland, W4MB
Mark J. Wilson, K1RO
Publications Manager 20 Conductors for HF Antennas
Michelle Bloom, WB1ENT
Production Supervisor By Rudy Severns, N6LF
Sue Fagan
Graphic Design Supervisor 30 A Prognosis of Amateur Radio Techniques
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Technical Illustrator By Warren Bruene, W5OLY
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Production Assistant 37 A Simple UHF Remote-Control System: Pt 3
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Nov/Dec 2000 1
Empirically Speaking
THE AMERICAN RADIO A
RELAY LEAGUE R R
L
The American Radio Relay League, Inc, is a
noncommercial association of radio amateurs,
organized for the promotion of interests in Amateur In the telecommunications world, it applications. I am still working on the
Radio communication and experimentation, for seems that new technologies come decoder.
the establishment of networks to provide
communications in the event of disasters or other along so rapidly that any one person We have been lucky at QEX to get
emergencies, for the advancement of radio art has difficulty keeping up. As a group, some outstanding pieces about state-
and of the public welfare, for the representation radio amateurs should not have to of-the-art transceiver and antenna
of the radio amateur in legislative matters, and
for the maintenance of fraternalism and a high worry about falling too far behind the design, among other topics. Perhaps
standard of conduct. power curve because we have some we should let you know some of what
ARRL is an incorporated association without
great magazines, Web sites and more is coming in 2001, and make a call for
capital stock chartered under the laws of the
state of Connecticut, and is an exempt organiza- communications gear than some large articles on subjects that seem to need
tion under Section 501(c)(3) of the Internal governments. What we see in the more coverage. First, we’d better tell
Revenue Code of 1986. Its affairs are governed
electronics trade press technically, you about what’s inside our last issue
by a Board of Directors, whose voting members
are elected every two years by the general though, is getting to be quite different of 2000.
membership. The officers are elected or from what we see in the amateur
appointed by the Directors. The League is In This Issue
noncommercial, and no one who could gain media. There may be many reasons
financially from the shaping of its affairs is for that, including a very different Robert Brown, NM7M, has studied
eligible for membership on its Board. distribution of frequencies of interest 160-meter propagation with great
“Of, by, and for the radio amateur, ”ARRL
numbers within its ranks the vast majority of to readers. For example, how many interest, and he gives us some results
active amateurs in the nation and has a proud hams are working with 2.4-GHz gear for a certain DX path on that band.
history of achievement as the standard-bearer in
in, say, New York City as opposed to Many effects that are found at those
amateur affairs.
A bona fide interest in Amateur Radio is the the number of commercial links near frequencies are not generally well
only essential qualification of membership; an that frequency? understood. Some may be unknown to
Amateur Radio license is not a prerequisite,
Well, the commercial wizards are neophytes and others remain unex-
although full voting membership is granted only
to licensed amateurs in the US. giving us the tools we need to jump plained even by experts. Robert goes a
Membership inquiries and general corres- into a lot of new technologies. Higher fair way toward helping us understand
pondence should be addressed to the
administrative headquarters at 225 Main Street, levels of circuit integration on chips them. R. P. Haviland’s series on quad
Newington, CT 06111 USA. and in subsystems are really making antennas continues (at last) with Part
Telephone: [phone] it easier for experimenters to try 3 and a treatment of multi-element
Telex: 650215-5052 MCI advanced technology. Amateur Radio designs. Tradeoffs among gain, beam
MCIMAIL (electronic mail system) ID: 215-5052
FAX: [phone] (24-hour direct line) has been and still is a wonderful width, impedance, front-to-side and
proving ground for almost anything front-to-back ratios are examined.
Officers
that potentially improves the way we Rudy Severns, N6LF, takes a
President: JIM D. HAYNIE, W5JBP
communicate. What we communicate careful look at various types of
3226 Newcastle Dr, Dallas, TX 75220-1640
hasn’t changed much in a while, but antenna wire to see how the charac-
Executive Vice President: DAVID SUMNER, K1ZZ
there may be new possibilities yet. teristics of different materials affect
The purpose of QEX is to: Some of you are undoubtedly certain designs. He gives a concise
1) provide a medium for the exchange of ideas wondering what happened to the next explanation of skin effect and why it
and information among Amateur Radio experi-
parts of two article series: John exists. I wasn’t sure I remembered
menters,
2) document advanced technical work in the Stephensen, KD6OZH’s “ATR-2000: A how to explain why it exists very well
Amateur Radio field, and Homemade, High-Performance HF at all until I read Rudy’s sidebar.
3) support efforts to advance the state of the
Transceiver” and my “Perceptual Warren Bruene, W5OLY, wrote a
Amateur Radio art.
Transform Coding.” We may have led report almost four decades ago that,
All correspondence concerning QEX should be
addressed to the American Radio Relay League, you to believe they had disappeared when combined with his updated
225 Main Street, Newington, CT 06111 USA. forever, but the fact is that each author prognosis, forms a very telling story
Envelopes containing manuscripts and letters for has had to take a hiatus to work on of Amateur Radio. We publish them
publication in QEX should be marked Editor, QEX.
other projects. John indicates he will here in the hopes that future hams
Both theoretical and practical technical articles
get cracking on his Part 3 soon. My will read them and get a new set of
are welcomed. Manuscripts should be submitted
on IBM or Mac format 3.5-inch diskette in word- Part 2 will appear sometime early next bearings from the past. We find that
processor format, if possible. We can redraw any year. I want to have sample audio files new ideas and concepts are often
figures as long as their content is clear. Photos (.WAV format) of coded and decoded rejected out of hand before they have
should be glossy, color or black-and-white prints
of at least the size they are to appear in QEX. voice available for downloading before a chance to come to fruition. Many do
Further information for authors can be found on we publish the article. not bear fruit anyway, but it is
the Web at www.arrl.org/qex/ or by e-mail to When I built my analog frequency interesting to measure our vision,
[email protected].
compressor and coded a speech signal both backward and forward in time.
Any opinions expressed in QEX are those of
to reduce its bandwidth from 15-kHz Bill Sabin, W0IYH, discusses the
the authors, not necessarily those of the Editor or
the League. While we strive to ensure all material to less than 4 kHz, the result was not properties and use of thermistors—
is technically correct, authors are expected to quite what I expected. I thought the resistors that change their value
defend their own assertions. Products mentioned compressed signal would still be significantly over temperature. These
are included for your information only; no
endorsement is implied. Readers are cautioned to intelligible, but it is not. That may be
verify the availability of products before sending a problem for Amateur Radio Continued on page 19
money to vendors.
2 Nov/Dec 2000
On the SSW Path and
160-Meter Propagation
How do the complexities of the ionosphere make
160-meter DX possible? Here’s the story from an expert.
By Robert R. Brown, NM7M
Itis well known that radio results when there is spatial structure hours of darkness. Then natural
propagation takes place be- in the ionization, as with field-aligned gradients of importance to propagation
cause of ionospheric refrac- irregularities in auroral displays on that band are those below and above
tion, reflection or scattering of during magnetic activity. the nighttime E-region peak and
RF waves. Of these three modes, The theory of electromagnetic-wave around the sunrise/sunset portions of
refraction and reflection involve ex- propagation by refraction goes back to the terminator. In the D region, the
tremes of electron distributions. Thus, Snell’s Law, which in turn is based on ionization of electrons is caused by UV
refraction takes place when the Maxwell’s Equations. It shows that and X-rays in starlight, by galactic
electron density varies slowly over a signals deviate from straight lines in cosmic rays and by solar photons
region having extent greater than a proportion to the electron-density gra- scattered into the dark hemisphere by
wavelength in all directions. Reflec- dients along a path. Thus, familiar the high atmosphere: the geocorona. As
tion involves distributions with strong earth-ionosphere hops in the vertical a result, VLF (3-30 kHz) signals are
gradients, the electron density chang- plane result from the vertical gradient ducted back and forth between walls of
ing rapidly in a region small compared in the distribution of ionization above a waveguide, whose walls are the
with a wavelength. Scattering is be- the curved path, while lateral devia- ground and the lower D region.1
tween the two with regard to the tions from great-circle paths result While wave reflections off the
distribution of ionization and often from the gradients in electron density bottom of the D region may treated
transverse (or perpendicular) to the with a formalism similar to that used
1105 27th St #AW110 great-circle direction. for metal mirrors, a complication
Anacortes, WA 98221 Let’s consider 160-metereter DXING,
[email protected] which is usually attempted during the 1Notes appear on page 9.
Nov/Dec 2000 3
arises because of the presence of the directional features of verticals. Thus, That type of DX propagation, with
Earth’s magnetic field. In particular, a the use of Beverage antennas has signals guided for great distance along
rotation or shift of the plane of become very popular, as well as the use the terminator, has been widely
polarization may occur (see Note 1). For of smaller, directional antennas such accepted by DXers. While not said
example, a wave incident at the bottom those of the flag or pennant type. explicitly in so many words, the
of the D region having its E vector in In the last decade or so, considerable interpretation of the observations rests
the vertical direction may, on reflec- attention has been devoted to DXing on on wave refraction as a basis. But it has
tion, still have a vertical component of 160 meters. This has been heightened not been without criticism by the
polarization, but also a horizontal one, by the number of major DXpeditions to ionospheric community in the Amateur
as well. Such mode conversion, as it is Asia that have included 160 meters, Radio circles because efforts using ray-
called, serves to change the wave with XZ0A in Burma as a recent exam- tracing methods with the PropLab Pro
polarization, particularly on long paths ple. In this regard, a winter path from program (Oler, 1994)5 and both the
with many reflections. those regions has been singled out as CCIR and URSI model ionospheres6
Above the E-region peak, the vertical quite productive for DXing from the (IRI, 1990) have failed to verify its
gradient at night is unique in that its USA, along the SSW sunrise term- existence. In addition, it is not clear just
sign or direction reverses across the inator. what controls where signals become
bottom of an electron-density valley. That differs markedly from the more coupled to the terminator region nor
The valley, shown in Fig 1, grows conventional short path across the how they become decoupled.
progressively deeper in the darkness, darkness at auroral and polar lati-
away from the terminator and contri- tudes. An example is given in Fig 2, Failure of Wave Refraction
butes to stable ducting of signals in the which shows that both the short path As noted above, terminator guidance
vertical plane. In that same region, and the proposed path between the Far of RF signals was studied initially by
horizontal gradients in electron density East and Midwest at the winter ray-tracing methods to see if it was
are responsible for the horizontal devi- solstice. That type of path meets the possible to have 160-meter signals fol-
ation, or transverse skewing, of ray terminator in the Indian Ocean area low the direction of the terminator—
paths; but in contrast to the vertical and then leaves it in the South Pacific say parallel to it but some distance
gradient, the horizontal gradient is area. It has received considerable away from it. While the possibilities are
continuous in direction, with ionization attention4 in DX circles, with the infinite, some tests showed that ray
always decreasing away from the suggestion that 160-meter signals may paths, starting close or parallel to the
terminator. be guided across great distances in terminator would deviate away from it,
Unless specified otherwise, discuss- darkness by the ionization inside the going deeper into the dark hemisphere.
ions of propagation assume wave terminator. In addition, wave propa- Those paths were obtained by using
refraction in an ionosphere that is gation in that direction has been the PropLab Pro program, in three
parallel to the surface of the Earth; considered as a form of long-path dimensions. That program solves the
however, irregularities may be present propagation, with signals going far equation of motion that governs the
that would tilt the ionospheric layers greater distances than more-conven- advancement of a ray path, first intro-
and reduce the scale of regions of tional short paths from DX targets. duced by Larmor in 1924:
constant electron density. That would
break up the extent of coherent reradia-
tion in the ionosphere and result in
propagation closer to scattering, with
waves going off in other directions than
just the forward.
In addition, in disturbed, non-equil-
ibrium conditions, other forms of ion-
ization gradients may be present
because of an influx of energetic
electrons2 during an aurora or because
of their release from the Van Allen
radiation belts3 during major magnetic
storms. Those gradients may be quite
large, with horizontal structure as well
as scales small compared to a wave-
length and organized by the local mag-
netic field. In such circumstances,
gradients may shift propagation from
scattering to wave reflection by small,
intensely ionized regions.
160-Meter Propagation
With regard to 160-metereter opera-
tions, transmitting antennas frequent-
ly use vertical polarization. Receiving
antennas, on the other hand, are often
chosen to focus on a limited range of Fig 1—Electron density distributions for location near to (right) and far from (left) the
directions instead of having the omni- terminator at night.
4 Nov/Dec 2000
minimum; instead, it always de- go with a ray following the terminator
dθ=−1dn (Eq 1) creases away from the terminator. So, half-way round the Earth: a change of p
dS n dl there is only one type of gradient: one radians over a distance of 20,000 km or
This equation is the differential form that refracts signals horizontally 1.57×10–4 radians/km.
of Snell’s Law of refraction. It gives the away from the ionization and only con- With that curvature in mind and us-
rate of change of ray direction dθ/dS tributes to instability. Moreover, the ing the International Reference Iono-
along the path S, in terms of the index rate of deviation on a signal path spheres, the index of refraction and
of refraction, n, of the ionosphere and caused by density instability varies as horizontal gradient of density were
its spatial rate of change dn/dl in direc- the square of the wavelength, making evaluated at a path altitude of 130 km
tions perpendicular to the path, in both the effect of a given gradient even in the midst of the terminator region in
the horizontal and vertical planes. greater at lower frequencies. Fig 2. That rate of refraction would be
The search for a 160-meter path that So at best, the ray-tracing search on achieved at about 300 km equator-ward
advances horizontally by following the 1.8 MHz amounted to looking for a loca- of the terminator, as shown in Fig 3.
terminator resembles looking for a tion relative to the terminator where Again, though, remember that would
case of MF refraction in the lower iono- the horizontal deviation of a ray just not be a stable path that could be main-
sphere that is like HF propagation of matched the curvature of the termina- tained for any particular distance or
Pederson rays in the high ionosphere. tor, but resulted in unstable propaga- time. That situation is extremely un-
There, HF signals at the MUF may tion parallel to it. An estimate of the stable since the electron-density gradi-
travel long distances and yet move necessary curvature may be obtained ent is always the same magnitude and
along for awhile at a constant altitude, by noting the changes in heading that from the same direction at any given
parallel to the Earth’s surface. The HF
case is possible around noon (see
Note 1) as the electron density on the
path goes through a maximum at the
F-layer peak and gradients along the
path are at a minimum. As a result, an
unstable ray path forms just at the F-
layer peak; however, the presence of
any significant irregularity in electron
density would disrupt its precarious
equilibrium, because the gradients
would not be in directions that could
return to equilibrium.
In contrast to the preceding circum-
stances, an example of very stable wave
propagation at lower altitudes is found
in vertical ducting of MF signals in the
density valley above the nighttime E re-
gion, shown in Fig 1. In this case, the
gradients in the vertical plane are in
opposite directions above and below the
altitude of equilibrium of a ducted ray
and in such directions as to return a ray
toward equilibrium when perturbed.
With the MF case near the termina-
tor, however, the horizontal variation Fig 2—Short path across high latitudes from Burma to the Midwest at the winter solstice
of density does not go through any and a SSW path guided by the terminator.
Fig 3—Rate of horizontal ray deviation by refraction in the local
electron-density gradient at various latitudes, for SSW paths
parallel to the terminator. The points are for the winter solstice
and a longitude of 172°W. Note that each degree of latitude from
the terminator corresponds to 111.11 km. The horizontal line is Fig 4—A two-dimensional ray trace of signals from the first part
the rate of deviation of the terminator itself. of the path in Fig 2 and launched at 20°.
Nov/Dec 2000 5
distance along the terminator, and it haves according to current models. A lar origin there. The question remains:
does not reverse sign or direction about general feature of those models is that How do signals propagate from DX and
a minimum. ionization decreases steadily when go- yet appear, around sunrise, to be com-
ing away from the terminator. That is ing from a SSW direction?
Ionospheric Absorption another way of saying that there is no Since refraction by the known distri-
Path stability in the face of distur- other recognized or accepted density bution fails and signals from the SSW
bance is a matter related to ionospheric distribution that would have a horizon- are noted even in the absence of geo-
structure, but absorption relates to tal gradient in opposition to that of so- physical disturbance, wave reflection
more-fundamental ionospheric pro-
cesses, such as collisions of electrons
with their surroundings. Like refrac-
tion, though, it varies with the square
of the wavelength, or inversely with the
square of frequency. That being the
case, signals on the 160-meter band
suffer the highest rate of absorption (in
dB/km), particularly on E-hops. E-hops
are always the case if a path nears the
terminator.
The first leg of a path from Burma to
the Midwest, shown in Fig 2, covers a
distance of 8000 km to the terminator.
Over at least 5000 km of that, the path
consists essentially of F-hops, at least
for radiation angles in the 15-25°
range, which are typical of DX propa-
gation. The remaining distance is in E-
hops with heavy absorption. That is
shown by the two-dimensional ray
trace in Fig 4, for a launch angle of 20°.
Another view may be obtained by
using the integral form of Snell’s Law,
as may be shown by a plot of the
plasma frequencies in a vertical plane
along the ionospheric path. In that
formulation, signals are characterized
by an equivalent vertical frequency
Fig 5—A transverse plasma-frequency plot for the first part of the path in Fig 2. This is
(see Note 1) on entering the lower iono-
essentially a cross-section of the ionosphere with the transmitter at the lower left and
sphere. This is just like exploring the receiver at lower right.
ionization distribution by vertical
sounding. For a 1.8-MHz signal
launched at 15°, the equivalent verti-
cal frequency is 0.55 MHz; and in its
vertical travel, the signal will never
rise above the altitude of a 0.55-MHz
iso-contour in the plasma-frequency
plot. Similarly, signals launched at
25° have an equivalent vertical fre-
quency of 0.82 MHz and are limited by
their vertical excursions.
Fig 5 gives a plot of the transverse
plasma frequency for the first 8000 km
of the path from Burma to the termina-
tor. Note that 1.8-MHz signals launched
at 15° (on the left) will be limited to E-
layer heights in going the last 3000 km
to the terminator (on the right). Those
launched at 25° will be limited similarly
in going the last 1000 km. Those losses,
along with any further travel, would
reduce signals to unusable levels.
SSW Signals and an Alternative
Fig 6—A representation of short-path rays (sold lines) which are scattered (heavy
The discussion above shows that
dashed lines) at high angles from one turbulent region. The lightly dashed ray shows the
signal propagation near the terminator polar limit of the short-path rays and the heavy solid line shows the terminator. RX is the
is unstable when the ionosphere be- location of the receiver.
6 Nov/Dec 2000
by steep gradients is ruled out and an- constituents outnumber positive ions angles and heights of the ozone layer,
other mode must be sought. That leaves by far; with a high rate of neutral-ion when sunlight is just able to pass over
wave scattering as the only alternative. collisions, ions are carried along by the the layer to reach the D region. For the
Fortunately, in contrast to refraction, motions of the neutrals (see Note 1). case in Fig 7, the angle amounts to
scattering is capable of some large de- Electrons may follow positive ions be- 3.3°; using 80 km as a reference, the
viations in single-ray encounters, even cause of electrostatic attraction. height of the ozone layer is 69 km.
with small scattering regions.7 Now, the type of observations that
The scattering region that serves to Ozone Effects give results as in Fig 7 have been car-
bring us 160-meter signals has its ori- It is possible to correlate the sunrise ried out for well over two years using
gin in systems that operate at sunrise. effects of atmospheric ozone with low- 55.5-kHz signals from NPG in Dixon,
With turbulence, this region probably frequency propagation in the lower D California, to Guemes Island, Washing-
has quite a few small parcels of ioniza- region. There, the electron density ton. The basic data show how the height
tion—each less than a wavelength in gradient moves downward at dawn of the ozone layer varies throughout the
extent—in the area off to the SSW, from about 95 km to 70 km, when solar year. The results sample the seasonal
where the winter sun is already rising. UV begins to detach electrons from pattern: fairly stable across the sum-
Those irregularities would carry ion- negative ions formed during the night mer months, but with considerable
ization and perhaps reach the D and E (see Note 3). To detach these electrons, variation in height starting around the
regions to scatter incoming rays. Some UV must reach the lower D region by fall equinox, peaking around the win-
of the scattered RF would reach the passing through the ozone layer, ter solstice and then decaying toward
receiving station, as indicated in Fig 6, which is somewhat opaque to UV. By the equinox again in the spring.
but would give the impression that the noting the times of peak interference Within those variations, differences
signals came from a false angle. that result on suitable paths, it is pos- appear according to the basic weather
One way to study ionospheric irregu- sible to find when the gradient has pattern. Thus, Fig 8 shows the ex-
larities during winter is by looking at lowered to about 80 km, midway be- tremes of solar depression angles, week
turbulent aspects of the electrically tween the limits for night and day. by week, throughout 1998 when the “El
neutral atmosphere. Motions of lower Next, by noting times when the sig- Niño” dominated the US. Fig 9 shows
parts of the atmosphere and ionization nal intensity is at minimum, one may the extremes throughout 1999 when
are intimately connected as neutral use the data to find solar depression “La Niña” was over us. Please note that
Fig 7—Slow time variation of NPG signals at sunrise. Fig 8—Solar depression angles for LF intensity minima centered
on Dec 1998.
Fig 9—Solar depression angles for LF intensity minima centered Fig 10—Heights of the ozone layer in winter, 1999.
on Dec 1999.
Nov/Dec 2000 7
“wrap-around” was used to center the of the path. The results obtained by within a broad swath of ray paths at
figures on the winter months in 1999. that method obviously depend also on lower latitudes and arrive in North
Also note that the two sets of data are the size and number of the steps taken America at more westerly longitudes.
quite similar in their general features, in the numerical integration and the If those signals are to be heard in the
but the El Niño pattern in 1998 shows number of spatial dimensions used. US, they would have to be propagated
far more activity in winter, with mini- The next approach still involved by efficient modes, by either F hops,
mum depression angles separated less using the equation of motion for a ray E-F hops or ducting. In any event,
from maximum. path but only for spot values of the rate those paths would impact at ground
With the La Niña weather pattern, of refraction or deviation of the ray path level near the terminator as high-
there were times when large-scale at locations near the terminator. That angle rays, because of the downward
weather systems were infrequent. Dur- still involved the reference ionospheres tilt of the F-layer in that region.11
ing one period, a large, high-pressure and the geomagnetic field, but any However, the region will also be one
system over the Pacific Northwest questions about the uncertainties from in turbulence and signals reaching
lasted for almost a week. On that occa- the numerical integration methods there will be scattered over a wide
sion, the ozone layer was thrust upward were removed. range of angles. Some scattered signals
by about 20 km with the passage of the Lastly, the integral form of Snell’s may reach sites that are east of the
first front, then slowly it dropped down- Law uses data from model ionospheres high-latitude limit but still in
ward over the remainder of the week. and shows locations that a ray path may darkness, as shown in Fig 6. Therefore,
In any event, Fig 10 shows that, day reach through refraction, given its without any signals coming in directly
by day, the height of the ozone layer initial launch conditions. However, it by short path, those signals would
around sunrise in winter is quite vari- does not deal with details along a path appear to represent DX propagation
able, often rising or falling by 10-20 km. nor the signal intensity remaining after from the SSW. Nevertheless, other
A theory of propagation of waves in a reaching any location. With the path locations that lie within the swath of
gravitational field8 indicates that dis- under discussion, the integral form short-path rays coming from the north
turbances propagate, producing atmo- shows that any propagation or ray would not be aware that the signals also
spheric displacements that increase in guidance that goes close to the termin- reached them by scattering.
amplitude as they rise through regions ator involves E hops and the heavy With the advance of time, the sunrise
of lower density. Changes seen in the losses from the presence of low-lying terminator would move to the west.
ozone heights (50-70 km or so) point to ionization near that location. Being inclined to the north in winter, it
even larger effects in the neutral atmo- Each of those arguments gave results would slowly cut off scattered signals
sphere. Observed variability shows that were against the idea of signals from the SSW and move the scattering
that the atmosphere is anything but being guided by the terminator. Having region northward, giving a “searchlight
calm; instead, this variability suggests made those points and noting that effect” for stations at fixed locations.
that regions may have considerable magnetically disturbed conditions are
horizontal structure and motion. not suggested for the type of propa- Conclusion
That spatial structure would be in gation, it falls to wave scattering to The present discussion has dealt
the neutral regions, where ozone explain the observed propagation. That with a SSW path from Asia that has
serves as a tracer, but it applies to requires scattering centers and the been reported by a great many US
ionization as well, as noted earlier. So, turbulence at lower ionospheric alti- DXers around sunrise in the winter.
if the neutrals move up or down, east tudes in the winter months, as inferred Given its direction, it is termed a
or west, north or south, ionization from ozone recordings, provide the “skewed path” and is even considered
follows along and any 160-meter mechanism needed for propagation. a form of “long-path” propagation.
signals incident on the regions may Having demonstrated guidance of That interpretation, though, does not
then be propagated by wave scattering signals along the terminator is not rest on any physical principle, only on
in the process. From that, it is only a feasible for the distances involved, the its apparent geometry. When the
small matter to have the short-path question becomes “How does wave physics of the path are examined, it is
signals incident on the turbulent scattering contribute to the apparent clear that the path fails in its effective-
region off to the SW, with scattering propagation from the SSW.” There, it ness, being unstable in direction and
then bringing signals to the receiver. was proposed that the path may be subject to heavy, ionospheric absorp-
completed by signals being passed to tion in the terminator region.
Discussion the receiver by scattering of short- The alternate explanation offered
Various degrees of detail were path signals that reach a nearby here shows the path is not skewed to
involved in the examining the location: not the target station, but follow the terminator as a result of
question of whether 160-meter signals one in a turbulent condition resulting large-scale ionospheric structure;
are guided along the direction of the from sunrise. rather, it is skewed by local processes
termination. First, the ray-tracing To be more specific, for DX paths involving neutral constituents. Scat-
method used not only current models that go toward polar latitudes, there tering is obtained toward the receiver
of the ionosphere, like those from usually is a path that represents the by turbulence at sunrise in a nearby
CCIR or URSI, but also a model of the high-latitude limit of propagation on region of the atmosphere. Thus, the
earth’s magnetic field, say the a given day. That limit would be path is made up of two parts: one by
International Geomagnetic Reference determined either by the flux of low- refractions along a short path, and the
Field.9 In addition, the ray-tracing energy protons or solar electrons other by scattering of short-path sig-
method goes through numerical (polar drizzle) on the polar cap, or by nals at high angles.
integrations of the equations of motion field-line effects from the impact of the This article constitutes a rebuttal of
for ray paths,10 step-by-step, starting solar wind. The rest of the propagation an idea that is more talked about than
from the initial great-circle direction paths from the DX transmitter will be documented, at least in any sort of
8 Nov/Dec 2000