We have gotten into a pattern of improving propagation and band conditions over several of the previous sessions. This session marked a significant improvement over any of those. A check at 0600z suggested that the band was quite noisy and a CW QSO would have been difficult if not impossible. JT9 QSO’s would have been easy enough, however, with a variety of stations around North America.
Geomagnetic conditions have improved to unsettled levels which may have provided the necessary spark for a good session. The Bz is pointing slightly to the South and solar wind velocities are above 530 km/s but both Kp and DST values look significantly better than they have in the previous sessions:
Doug, K4LY / WH2XZO, checked-in via email, noting a number of projects at his station including some additional antenna work that will need to happen due to late Spring and early Summer storms.
Phil, VE3CIQ, reported one of the better sessions in many months and offers the following map as evidence:
Ken, K5DNL / WG2XXM, was testing a U3S and driving his 200-watt amp during this session as “transmit-only.” He reports that he was decoded by 16 unique stations and had 27 decodes from WH2XCR, three of which were after sunrise.
John, W1TAG / WE2XGR/3, reports that he decoded six WSPR stations and was decoded by seven unique stations including his first report from ZF1EJ from the Maine QTH.
Neil, W0YSE/7 / WG2XSV, reports that he heard KPH/KSF/KSM on 426 kHz after 0400z at 95-100% copy in QSB during Night of Nights 2016. This is a nice feat during the Summer. I also copied them, but on 17 MHz, and offer two recordings, including the opening message and a CQ:
A few years ago I actually copied them on 426 kHz from here in Texas during a peak while operating in one of our special events. I am very happy that the MRHS continues to operate this event.
Mike, WA3TTS, reports transcontinental propagation from WH2XGP and longwave broadcast Arabic language audio:
Regional and continental WSPR breakdowns follow:
There were no reports from the trans-Atlantic, trans-African, or trans-Equatorial paths.
In the Caribbean, Eden, ZF1EJ, experienced a huge night of reports unlike anything seen in months:
Laurence, KL7L / WE2XPQ, had no reports during this session.
Merv, K9FD/KH6 / WH2XCR, continues plugging right along through the doldrums with damaged antennas. The path to and from VK continues to be relatively stable:
Jim, W5EST, presents, “TRANSMISSION LINE ANALOGY: MF/LF RADIO WAVES ARE ABSORBED IN THE D-REGION MORE THAN HF”:
“E-region and F-region topics occupied the last two blog days–critical frequency, MUF and critical frequency geographies, and real-time ionograms. Now, what about the D-region?
Today’s two illustrations depict a shunted transmission line analogy (subject to 1st endnote*) for the D-region in daytime and nighttime. Below and above each of the D, E, F regions, an RF signal wave just sees 377Ω intrinsic impedance as if propagating on a transmission line. (Unlike a transmission line, however, the volume of transmitted RF signal power expands with distance and the RF signal strength diminishes.)
Ionospheric regions, in this analogy, each shunt the 377Ω “transmission line” with frequency dependent, region-specific distributed impedances spread through them.
The E and F regions each look like a near-short or a near-open shunt when the RF signal frequency lies below or above, respectively, the applicable path-dependent MUF of a region. By contrast, the ionized, dense, daytime D-region of the first illustration can be dissipative in a frequency-dependent manner.
HF higher bands (at left) see the D-region as if it were a relatively high resistance, near-open shunt across the 377Ω “transmission line.” So the HF higher band signal passes through the D-region with little disturbance and reflects from the F1 or F2 daytime F-region. On the way back down to receiver RX, the D-region again offers very little dissipation to this HF signal.
LF bands like 2200m (at right) see the D-region as if it were a relatively low resistance compared to 377Ω.** Many days the D-region somewhat reflects LF signals. Since the low shunt resistance introduces high “SWR,” so to speak, enough “reflected power” arises to yield a detectable signal at receiver RX. The rest of the RF signal power is unreflected and progressively dissipated as the RF drills into the D-region distributed resistance.
MF bands like 630m (in middle) see the D-region as a shunt resistance that’s more nearly “matched” to 377Ω. Since the D-region is a good match the SWR is low, and little or no reflection happens.
Why is the shunt resistance frequency dependent? July 11 this blog described how the same amount of power P can accelerate ionospheric free electrons to higher velocities at lower frequencies than higher frequencies can. Each faster moving electric charge means more current I. Resistance R is found by dividing power by current-squared: R = P / I2 .
In the second illustration, the nighttime D-region is so weakly ionized that it amounts to an open shunt. LF/MF/HF signals all traverse the D-region. The HF signals reflect from the nighttime F-region because their frequencies exceed the E-region MUF and lie below the F-region MUF. Higher-frequency HF signals and VHF mostly pass through all the ionospheric regions out to space– but with important exceptions as amateur radio operators have repeatedly demonstrated.
Nighttime LF signal frequencies lie below the E-region MUF, so the E-region looks like a shorted shunt and reflects the LF signals back to earth. If the E-region MUF exceeds an MF signal’s frequency, the MF signal also ascends through the D-region, reflects from the E-region, and descends back through the D-region to RX. Otherwise, if the MF signal frequency exceeds E-region MUF, the F-region reflects it instead (not shown).
Why do daytime 630m sky wave propagation events happen? Solar flares can additionally ionize the daytime D-region, to thereby decrease its “shunt resistance” and reflect more 630m signal. However, daytime 630m sky wave propagation events can happen even in the absence of a solar flare–and can fail to happen on a days when a solar flare is active! Daytime 630m sky wave propagation events are more numerous in the late fall and on into winter when the sun elevation is low. Other times of year, these 630m daytime events occur–but more rarely.
All these 630m daytime event and non-event observations suggest to me that the D-region is a physically dynamic medium wherein winds or turbulence can introduce patches of reduced ionization that permit MF signals to pass through with reduced losses and reflect from the E-region back through the reduced-loss D-region to a receiver. When a solar flare fails to produce an event, perhaps such winds or turbulence distribute solar flare ionization upward and more equally through the D-region. That way its distributed shunt resistance continues to have a dissipative outcome.
There’s probably some reference to credit for a D-region transmission line analogy. I will appreciate any citation you may offer, and any other information on a D-region topic you think useful. TU & GL!
* Doing a transmission line analogy is probably approximate at best, compared to a derivation directly from Maxwell’s Equations–not to mention the complicated geometry and dynamics of the real ionosphere of course. On the web, see an example of the Maxwell’s Equations/refractive-index approach by David Jenn, Naval Postgraduate School, Monterey, CA. http://www.dcjenn.com/EC3630/Ionosphere(v1.5).pdf
For MF/LF/HF slanting paths, a better transmission line analogy would probably call for characteristic impedance transitions instead of a lumped shunt model facing the RF entering ionosphere regions. The amount of impedance transition depends on the angle of incidence, the RF polarization, and the GMF. So the ionosphere presents itself different ways to different path lengths not only at different frequencies but even at the same frequency.
Brown, Sharpe & Hughes Lines, Waves and Antennas (1961) pp 122-138 shows a transmission line analogy for oblique incidence on dielectric (rather than plasma), with characteristic impedance formulas and simplified Smith Charts. http://www.amazon.com/Lines-Waves-Antennas-Transmission-Electric/dp/047106677X (No free copy seen on web: try Amazon or other web bookseller.)
**See also https://www.ngdc.noaa.gov/stp/space-weather/online-publications/miscellaneous/afrl_publications/handbook_1985/Chptr10.pdf . Among other topics, this reference discusses ELF whistlers passing through all the ionosphere regions and traveling transcontinental distances. Whistler frequencies are far below the critical frequencies for all of those regions! Scroll 1/3 to section 10.2.5 at p. 10-37. Moreover, p. 10-37 states that, at VLF, VLF signals have been detected at satellite altitudes.”
Additions, corrections, clarifications, etc? Send me a message on the Contact page or directly to KB5NJD gmail dot (com)!