Band conditions varied across the country but noise was elevated in most areas due to storms in the south eastern and north eastern US. The noise was elevated here in Texas but reasonable enough that WG2XKA was decoded here. John is located a long way away from me and as we move into Summer, his decodes will basically disappear until the Fall.
The geomagnetic field is storming again and protons were observed as elevated to high levels at 51 p/cc at 1831z. Prior to the beginning of this event, daytime conditions were really very good for March. Ken, SWL/EN61, in Indiana provided a number of reports in the late morning for my signal. Solar wind is also elevated above 500 km/s with a Bz that was generally pointing to the South.
Reports for John, WA3ETD / WG2XKA, are interesting. The main source of noise during this session was actually located in the Midwest as a storm system pushed eastward. So why didn’t John have more reports from stations in the West where noise was less of a problem? Session details below:
Mike, WA3TTS, reported G0MRF/p once again in spite of a storm system baring down on his QTH. Mike reports that he was QRT from 0130z to 0330z as the storm system plaguing the Midwest and north east moved through. It was at this time that the storm was in front of the antenna that was pointing to Europe, resulting in no further (or at least likely) chance for reports on that path.
Neil, W0YSE/7 / WG2XSV, Joseph, NU6O / WI2XBQ, John, VE7BDQ, and Toby, VE7CNF operated WSQ2 again, the very slow FSK mode by ZL1BPU. Neil notes early reports from Toby, a path of 232 miles in daylight:
Neil reported that he would be QRV again for WSQ2 QSO’s after 0300z. Activity was good with Joseph and Neil completing a WSQ2 QSO. That’s a relatively rare occurrence here in the US as WSQ2 has not found wide acceptance within the experimental community. There are a couple of perspectives on this QSO, seen below, in addition to transcripts from John, VE7BDQ, and Neil, WG2XSV.
In Europe, Luis, EA5DOM, reports on the RSGB-LF reflector that his 105 mW TPO signal has been yielding extraordinary reports. Luis reported some time back that he had a failure on the QRO PA and has been operating at QRP TPO since that time.
Roelof, PA0RDT, once again reported Joe, VO1NA, aurally. The persistence of this path is remarkable.
WSPR activity was down during this session. Around 0200z 69 MF WSPR stations were observed on the WSPRnet activity page. K1UTI returned to receive duties during this session after some time away. PJ0PJE had some type of problem that made an absolute mess of the MF 24-hour WSPR map. I don’t know if the problem was related to band selection of something else but its rendered the worldwide view and the view of Europe in particular almost unusable. Let’s be careful out there!
Regional and continental WSPR breakdown’s follow:
There were no WSPR reports from the trans-African path, however, ZS1JEN was present during the session. UA0SNV was also present during this session but had no reports in the WSPRnet database.
The trans-Atlantic path continues to show promise, with more reports from WG2XKA in Europe as well as G0MRF/p making it “across the pond” for a second consecutive session, being reported by WG2XPJ and WA3TTS/2.
EA8/LA3JJ, provides reports for Tom, G8HUH, and David’s portable operation as G0MRF/p.
In the Caribbean, south eastern US storms impact reports by Eden, ZF1EJ. He still successfully recovered four stations from the noise.
In Alaska, Laurence, KL7L / WE2XPQ, reports increased absorption during the session. Nevertheless a few reports were available on the path to the South.
In Hawaii, Merv, K9FD/KH6 / WH2XCR, received reports from Australia once again as the storm system preventing decodes are now diminished or moved on. John, VK2XGJ, notes that his duplicate report from 1024z was from a parallel receive system. Merv also reported VK3ELV and VK4YB. With storms in the eastern US, no reports were found East of the Mississippi river.
In Australia, Phil, VK3ELV and Roger, VK4YB, received reports from WH2XCR. VK3ELV received an additional report from JH3XCU.
Jim, W5EST, provides an analysis of the anatomy of lightning in an discussion entitled, “LIGHTNING UP CLOSE”:
“Nature is a dominating LF/MF “operator” when it chooses to go QRV in your geographic region. Understanding tropospheric charge dynamics, and lightning especially, not only helps us construct safer TX and RX stations. Safe station construction can also reduce local manmade QRN pickup into our receiving arrangements. Understanding the geographic distribution of lightning on any given night or day helps us interpret SNRs and avoids confusing some SNR variations with propagation events. Someday lightning knowledge may even help us create more fully noise-resistant digital signal processing software for station use.
A single tooth-shaped lightning stroke waveform at ten-microsecond time scale is equivalent to the combination of a whole set of sine waves having frequencies and phases distributed over a very wide frequency range. Lightning RF in the geographic region of the RX station follows a fairly direct path to the RX. I am currently trying to learn whether the sine waves of the lightning strokes in the same half-second lightning strike can destructively interfere with each other in a frequency-dependent way. Like TX station RF, 630m lightning strike RF from remote distances can propagate by sky wave reflection from the ionosphere.
Radiative emission is 4th-power in temperature. That’s ~15,000°C for lightning, which means that much lightning energy is dissipated in the infrared and shorter-than-micrometer wavelengths. What energy remains goes to compression waves and VLF/LF/MF/HF radio emissions. Lightning strokes suddenly heat humid air to plasma to create a sonic explosion emanating radially from the crooked line of the path.
ENERGY (KWH) IN A LIGHTNING STROKE: If 20KA average current flows for 10 microseconds through 10Ω of earth, the energy that stroke delivers into the ground (or into your shack if it’s unprotected) is I2R δt = (2×104 amp)2 10Ω x 10-5 sec = 40KJ =1/100 kilowatt hour. Instead, most of the lightning energy is dissipated in the overhead lightning path, and not at ground level. The RF static crashes from lightning in our radios are derived from the radiation-efficient lightning stroke channel length that matches MF/LF wavelengths so well.
A 2007 Baba and Rakov paper* considers lightning return stroke models that picture lightning as a straight, radiating RLC transmission line with characteristic impedance Z = 130-470Ω. It’s not the actual crooked lightning geometry. We experimenters would say it’s like a vertical antenna model with pulsed RF. The models are linear or they put a simple step nonlinearity at the traveling pulse front.
In the modeling, a 1km-2km lightning channel has resistance = 600Ω – 2500Ω. Quality factor Q = ~10 for the channel. Return-stroke wavefront speed is 1/3-2/3 speed of light, or velocity factor 0.3 to 0.7. Return stroke channel resistivity is 1 Ω/m, comprised of ~0.035 Ω/m behind its return-stroke front and ~3.5 Ω/m ahead of front. For frequencies above 1 MHz, channel inductance L = 2.1 uH/m and inductive reactance ωL0 = ~13 Ω/m. (3cm radius, 500m up). Distributed capacitance C=50pF/m. A 5Mvolt, 12kA strike from height 2 km down to a 200m tall tower has rising voltage front 500KV/m and rise time 1 microsecond.
LIGHTNING AND ITS GENESIS: A stepped leader** is an invisible channel for electrons in the cloud to initially probe their way to the ground in jagged 50-100 meter segments, halting temporarily for about 50 microseconds at a time as they go. Then a positively charged spark from some ground-based object connects upward to the stepped leader. Return stroke current from cloud to ground now strongly incandesces the centimeters-wide channel. Another leader, the “dart leader,” may descend the channel. A subsequent return stroke can propagate upward from the ground to the cloud. Strokes can alternate 3-4 times in about half a second.
During, say, a one-millisecond time interval in the middle of a given one lightning stroke, lightning’s plasma channel is probably much more nearly like a linear circuit than is the nonlinearity of a whole 500 millisecond multi-stroke up/down lightning strike.
Lightning stroke channels are contorted by wind and magnetic forces and by cooling and reheating of the plasma channel from one stroke to another. Quenching may separate the strokes and does terminate a whole multi-stroke lightning strike event. Unlike an RLC circuit that does a damped oscillation based on one frequency, this non-linear RLC “vertical antenna” with its time-varying R, L, and C values is converting some energy generated at 630m into other frequencies. It’s also converting RF energy it generates at other frequencies into 630m RF.
Can you help make LF/MF stations more noise resistant? Tell us about your lightning experiences and ideas!
*Y. Baba, & V.A. Rakov. (2007). Electromagnetic models of the lightning return stroke. J. Geophysical Research, 112: D04102-4118. http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CDEQFjAC&url=http%3A%2F%2Fwww.lightning.ece.ufl.edu%2FPDF%2FAGU%2FBaba_Rakov_2007a.pdf&ei=APJUVZOHBMKwggSJmYCIDQ&usg=AFQjCNELjjuUxPCd8LxI31N762wQKLqAtg
V.A. Rakov. Characterization of Lightning Electromagnetic Fields and their Modeling. http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CCcQFjAB&url=http%3A%2F%2Fwww.lightning.ece.ufl.edu%2FPDF%2FZurich%2F1T01.pdf&ei=APJUVZOHBMKwggSJmYCIDQ&usg=AFQjCNESYDaEEAOz6KidsWQem5O5fyGqWQ&bvm=bv.93112503,d.eXY Rakov (U. of Fl.) lightning modeling paper. FIG. 1 shows graphs of electric E and magnetic B field intensities versus time at various distances up to 200km, adapted from 1979 work by Lin et al. The return stroke and subsequent strokes (dotted) are superimposed in FIG. 1 and have similar shapes.
J.R. Lucas (2001). High Voltage Engineering.
A.R. Jacobson et al. (2000). “FORTE radio-frequency observations of lightning strokes detected by the National Lightning Detection Network”, J. Geophys. Res., 105, D12, pp.15653-15662.
Additions, corrections, clarifications, etc? Send me a message on the Contact page or directly to KB5NJD <at> gmail dot (com)!