This session brought more unsettled geomagnetic conditions along with more terrestrial storms and storm potential. Several stations, including myself, were experiencing persistent Internet problems which hampered the process of reporting. At 0800z, after a self imposed session QRT due to storm potential in my area, I opted to put the station on the air and had a pretty good four-hour session. This was in contrast to many of the reports coming from further North. Activity actually seemed to be better much later in the evening and overnight than it had been earlier in the session.
Geomagnetic activity ranged from unsettled to quiet conditions. The Bz is pointing to the South and solar wind velocities are in the low category below 400 km/s. DST has recovered over the past 24-hours.
Steve, VE7SL, reports that the CW signal of WI2XJQ was RST 599 +10 dB at 0400z. Rick’s station improvements are paying off. Steve adds that he decoded five WSPR stations and was decoded by five unique stations.
Larry, W7IUV / WH2XGP, reports that his internet is also working again although the session was poor. Larry decoded three WSPR stations and was decoded by twelve unique stations during his time on the air.
Neil, W0YSE/7 / WG2XSV, was alarmed at the lack of activity near his bedtime but he did have some reports during the session from local stations:
Ken, SWL/EN61, in Indiana reported very poor conditions, decoding only eight signals the entire session, all of which were from me after 0800z:
Regional and continental WSPR breakdowns follow:
There were no reports from the trans-Atlantic, trans-African, or trans-Equatorial paths during this session.
In the Caribbean, Eden, ZF1EJ, reported my station early this morning. Eden noted that he would be inactive until Sunday:
Laurence, KL7L / WE2XPQ, reports that he decoded WH2XGP, VE7SL, and WH2XCR during this session but tried a different software configuration that did not work out so well. Laurence reports that he is now losing about 5 minutes of daylight each day, half an hour or more a week! I am envious! Then again, it actually gets dark here during the Summer.
Merv, K9FD/KH6 / WH2XCR, was hearing VK3ELV during this session so it seems that the hurricane-related storm noise has improved. He also heard me numerous times during my abbreviated session:
Jim, W5EST, presents “PART 2: THEORY JUNGLE SAFARI IN E & F LAYERS”:
“In yesterday’s blog, I suggested that Appleton-Hartree-Lassen (AHL) challenges 630m operators to set up more than one RX antenna and shoot-out multiple RX antennas with multiple receivers and decoders. Look for the unexpected. Null out a desired signal in a loop null and see if you can isolate a high angle return or a skewed return of that signal, and time of day it happens. Try spaced-apart loops in perpendicular vertical planes–see what polarizations E/W, N/S, and what circular polarizations you can detect.
Today, we continue the theory jungle safari I embarked upon yesterday. See AHL at https://en.wikipedia.org/wiki/Appleton%E2%80%93Hartree_equation
Today’s theme is: What doesn’t AHL tell us?
AHL by itself does not tell to what skew direction a signal ray will reflect. That’s where physical reality and Maxwell’s Equations make a second appearance together with AHL.
Physical reality: The contour surfaces of electron concentration can tilt in the ionosphere relative to horizontal.
What do the electromagnetic equations in the theory do? Maxwell’s equations constrain RF ray refraction from contour i to contour i+1 to follow a predicted relationship called Snell’s Law based on the refractive indices n provided by AHL:
ni+1 / ni = sin θi / sin θi+1
https://en.wikipedia.org/wiki/Snell%27s_law . (Mentally dividing ionospheric regions into contours and numbering them with indices i is just a convenience to describe smoothly spatially-varying levels of free-electron concentration.)
Moreover, Maxwell’s equations constrain both refraction and reflection, when reflection occurs, to a plane common to the ascending ray and the normal line perpendicular to the contour surface, whatever the tilt. And, like a mirror, the angle of reflection of the RF ray is constrained to be same as its angle of incidence in that common plane.
“Reflection” of an RF signal ray at altitude is a shorthand word here for refraction by successively different levels of electron concentration as the RF signal traverses an arc through an ionospheric region. The shape and horizontal extent of the arc is a consequence of Snell’s Law and the electron concentration profile of the ionospheric region. Although 630m low-MF will differ in detail from HF behavior, see HF illustrations at: http://www.ferzkopp.net/Personal/Thesis/node8.html
Now revisit a tilted contour surface. Think of an imaginary line perpendicular to any given contour (The line is called a “normal line,” simply meaning perpendicular.) If the normal line tilts from vertical but still lies within a vertical plane through the great circle between stations, an RF signal wave ascending along the great circle executes vertical skew when it reaches the ionosphere and gets reflected.
Vertical skew can introduce an additional reflection that way, additional to a mid-hop reflection point halfway from TX to RX. The vertical skew reflection point lies elsewhere than mid-hop geographically to reach the RX station. If mid-hop reflection and vertical skew reflection signals both reach RX in-phase, your SNR can enjoy a favorable bump.
Another skew type is lateral skew. The normal line is off-vertical, but this time the contours tilt sidewise. Both vertical and lateral skew can also result from a reflection. The RF signal wave laterally skews away from great circle propagation.
Of course, you usually don’t directly know the tilt and position of an ionospheric contour surface of electron concentration that reflects your RF wave. But you may notice skew effects contributing to SNR and affecting the heading of signal arrival. A rotatable loop with a sharp null set to an off-great-circle heading can help you discern if significant lateral skew occurred or not from a given TX station.
With a rotatable loop, you might even find two null headings for the same TX station in the same half-turn of bidirectional loop rotation. WSPR, CW and QRSS can favor antenna-rotation search for skew. Use ARGO (or similar software) QRSS3 or CW-mode imaging of any of those modes. WSPR’s 2-minute long transmissions may confuse skew with QSB when you try to interpret the WSPR2 decoder SNRs at different loop headings. Regardless of mode and method, e-mail us credible MF/LF skew results for this blog.
Turning to O/X waves, the AHL formula by itself does not determine the relative amplitudes of O/X waves as far as I can tell.* If you know differently, please write in.
O/X waves result from the two refractive index values of magnetized plasma when RF energy encounters an ionosphere region–insofar as the RF direction of propagation lies perpendicular to the GMF there. The angle between the RF signal ray and the GMF significantly affects the production of O/X waves and the refractive indices that they “see.” In either the northern or southern hemisphere, E/W paths at mid/low latitudes lie nearly perpendicular to GMF, as do paths in any direction at high latitudes.
By contrast, when the RF on an N/S path at mid/low latitude is parallel to GMF at altitude, right and left circularly polarized components of the RF wave “see” two corresponding refractive indices that alter the phasing. So various forms of elliptical polarization are possible. Transatlantic (TA) paths cross mid-latitudes and high latitudes. A mixture of effects is not unlikely on TA due to GMF being parallel to ray at mid-latitudes and GMF perpendicular to ray at high latitudes.
Suppose some of your 630m RF launches at a given favorable elevation angle for reception at a given RX station west or east of you. That 630m RF probably becomes divided in the E-region into O/X waves. The O/X waves reflect overhead at different geographic locations in a hop. Because of the different “points” of reflection, say the O-wave reaches the RX station and the X-wave is reflected elsewhere. But some of your 630m RF that ascended at another elevation angle of your TX antenna pattern may divide into an X-wave that reaches the RX station while the O-wave part of that RF reflects elsewhere.
Especially on single hop, the RX antenna quite possibly receives both O and X waves arriving at somewhat different O-specific and X-specific elevation angles of arrival respectively. The O and X waves have traveled different paths at different rates, so they arrive with different phases. If their amplitudes are comparable, the O/X waves can mutually interfere and they can significantly alter the received signal strength compared to either O or X alone.
Now consider a different situation: Suppose the electron concentration in the E-layer, and the GMF and RF signal ray geometry, are such that either or both the X-wave or O-wave in your 630m RF passes through the E-region without reflection. In that case the RF signal, or part of it, may be reflected by the F-region instead. That could lead to one or more long distance F-hops or to ducting between ionospheric regions.
More coming in a future blog post! GMF storms!
*http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&ved=0ahUKEwjX1oDVmIPOAhUO32MKHaDbCrYQFgguMAM&url=http%3A%2F%2Ftheory.physics.helsinki.fi%2F~plasma_jatko%2Fasp2014%2F4_Wave_propagation_2014.pdf&usg=AFQjCNGMVFsGI3egFV9dwJDTZlNvRp0ZyA Slides 18-26. Physics, Helsinki, Finland. 2014. (Unattributed, undated, but well done slides.)”
Additions, corrections, clarifications, etc? Send me a message on the Contact page or directly to KB5NJD gmail dot (com)!