This session was average, with moderate noise levels but it really depends on where you are located as to whether the band was quiet enough to operate or not. In the Northeast, for example, storms continues to create not only safety issues but also hearing problems.
Geomagnetic activity was quiet and the Bz ranged from unity to slightly North-pointing. Solar wind persists in the low category below 350 km/s. Solar X-rays are elevated, as reported by Solarham.
Edgar Twining posted this advice for would-be long-haul receive stations below the AM broadcast band on the VK 600-meter yahoo group.
Phil, VE3CIQ, reports that he decoded WSPR signals from PZ1GIA, WG2XXM and WH2XGP. The PZ station is likely not real and either a receive artifact or a database error as the call sign does not valid and does not have a user registration on WSPRnet. Phil was decoded by K4LY, SWL/K9, VE2PEP, WI2XFI and WI2XHK.
Ken, K5DNL / WG2XXM, reports that the band was about 10 dB quieter than the previous session. He decoded three WSPR stations and was decoded by seventeen unique stations including seventeen decodes from WH2XCR with the last one coming ten minutes after local sunrise in Oklahoma.
Neil, W0YSE/7 / WG2XSV, reports that he is close to being back on the air:
“John, I got several decodes of ur wspr this session. I was using my eprobe with my W0YSE/E call again. Perhaps I will get my XSV radio back online today….hopefully.
Hearing: VE7CNF, WG2XIQ, WG2XXM, WH2XCR, WH2XGP many times each…
73 from beautiful Vancouver, WA….”
Regional and continental WSPR breakdowns follow:
There were no reports from the trans-Atlantic, trans-African, or trans-Equatorial paths. ZF1EJ was reported at present but had no reports during the session.
Laurence, KL7L / WE2XPQ, was inactive during this session.
Merv, K9FD/KH6 / WH2XCR, experienced better band conditions to North America and Australia than recently observed:
Jim, W5EST, presents “ALASKA SUMMER, 630M POST-SUNSET: WHY DID XPQ’s LOOP AND OMNI TRADE SNR PLACES?”:
“Laurence KL7L WE2XPQ sends us this message about his high-latitude experiences:
‘What about at local sundown in Alaska–ignoring most of my path has to cross the mountains and glaciers at not less than 6 degrees elevation. – Could the OXO skew (whenever one wins) be worse in one path? Could the skew cause the omni to get signals on this skew for around 30 minutes around sundown time versus my huge loop which is pointing great circle to Texas? – Then things “stabilize”, as much as they do in AK J, and the path skew reduces and hence the loop then wins…?’
Refer to the illustration. Hypothetical paths between WH2XGP, Washington state, and WE2XPQ will occupy this response, since XGP reaches XPQ more consistently this midsummer than the more distant stations in Texas/Oklahoma do into XPQ. I read Laurence’s message to imply XGP RF signal-heading would approach the heading of a loop null at WE2XPQ because of skew. So the omni wins for a while in this post-sunset (SS) regime before loop once again becomes superior.
If a rotatable loop were available, the skew idea can be tested by orienting the loop to favor south or SSW heading. Then presumably both loop and omni would do well at sundown since RF signal would skew into both. After that, the omni would outperform the loop the rest of the night because the great circle path would be in the loop null.
Sundown suddenly decreases the solar ionizing radiation encountering the ionosphere. In Alaska, early-mid July means the terminator (grayline) moves through the region sideways. Anchorage AK sunset (SS) heading July 17 was 320°, or almost straight NW. Anchorage SS time was 11:12pm, 0712z. Anchorage AK sunrise SR heading was almost directly NE: 39°, 4:57 am, 1257z.
These AK SS/SR times are consistent with XPQ’s decodes of XGP’s signal in July, 2016. WSPR database entries for XGP-xpq start 1-2 hours after AK SS and end 1-2 hours before AK SR.
In the post-SS propagation regime, I believe that ripples and sinkholes (downward plumes) in E-region and D-region ionosphere may be somewhat active. Regarding possible skew effect of ripples, consider the perpendicular orientation of terminator at SS in Alaska relative to great circle path. I’d expect most ripples, if they indeed exist, to run roughly parallel to the terminator and orient SW-NE. The ripples would be somewhat more like parallel relative to the hypothetically-skewed arriving XGP signal from south or SSW of Anchorage. Thinking three-dimensionally (3D) about skew at altitude is challenging but worth the effort.
Next, consider the great circle path length 2455 kilometers, WA-AK, XGP-xpq. Subject to radio shadow of nearby AK mountains at each heading, that 2455km path length might support low angle 1-Ehop but more probably the somewhat more elevated 2-Ehop or 1-Fhop mode. I suspect 1-Ehop would be shadowed by XPQ’s mountains. If skewed, 2-Ehop or 1-Fhop would also very probably be needed to cover the longer total distance than 2455km that segments of a skew path would accumulate.
XGP-xpq SNR and XGP-kl7l SNR have been peaking some July days in strong minus teens and even minus single digits. One XGP-xpq propagation scenario involves 2-Ehop. In that scenario 2nd sky reflection could happen at one-quarter of 2455km–or 615km–away from XPQ’s QTH.
You might think that high ray elevation angles and vertical skew to low angle at altitude could form solutions for this path, and perhaps they might. Just keep in mind that a 2-hop midpoint reflection will probably have equal angles of incidence and reflection. Equal angles at the surface reflection constrain the ray elevation angle that would be effective for XGP in WA to launch, and the ray arrival angle for that XGP ray to actually reach XPQ.
Next, consider where skew happens. I presume that skew only happens in ionized plasma and that O/X wave formation only happens in such ionized plasma that’s permeated with geomagnetic field GMF. For XGP to arrive from the south or SSW into XPQ’s loop null, an ionosphere region like E or F is responsible for the skew and not any un-ionized spaces beneath or above it. The geographic path segment between two skew reflection points is great circle, as the illustration of the long middle segment between skew points shows. For 2-hop there’s a surface reflection point that bisects that long middle segment between the two supposed skew reflection points in the ionosphere.
If a skewed arrival path from the Pacific Ocean south of Anchorage is correct, then I think the most nearly plausible account (see illustration) requires most of that skew to happen as close to AK as possible. Why? Because that’s where the GMF is stronger and more steeply inclined.
In a 2-Ehop scenario, the skew happens at E-region altitude roughly 615km south of XPQ. Additionally, some skew (just less of it) is happening on XGP’s first hop roughly 615km west of WA over the Pacific Ocean as the imagined RF skew path angles NW and then skews sharply more nearly northward to go on into the Anchorage area where XPQ receives XGP.
Could the RF be skewing over an inland point instead? Possibly, if it were 1-Fhop. If 2-hop, the extra ground reflection loss somewhere in northern British Columbia would make Laurence’s description unlikely I think. I’ve drawn alternate paths, one skewing to the left over land and the other skewing to the right over water simply because I don’t know at this point which way the skew happens. Appleton-Hartree could probably help me make a more considered statement about which way is physically likely.
Now let’s consider the angle of skew as seen from above and shown in the illustration. The XPQ RX loop plane lies along a great circle path to Texas, and that great circle runs through Montana, east of WA. Loop null may therefore be SW/NE, perhaps SSW/NNE. Depending on the loop antenna pattern, skew angle would need to diverge 60 degrees or more from straight ahead propagation to impose significantly diminished loop sensitivity to XGP due to the loop null heading. I’m assuming a bidirectional loop and you’d analyze the azimuth pattern to assess this.
Can we rule out high angles from XGP’s signal elevation angle of arrival into XPQ? Recall that a loop is comparably sensitive or even more sensitive to high angle incoming signals compared to a vertical omni. That implies the incoming signal is not greater than 30°–not high angle elevation–when the loop is underperforming compared to XPQ’s omni. Yes, high angle signal arriving with a polarization perpendicular to the loop plane could cause a low SNR polarization null. But I think that’s geometrically unlikely. Moreover, polarization would vary enough over the space of an hour to deliver some strong decodes at XPQ anyhow, in my opinion.
E-region ionization and plasma frequency. An hour or two after AK sundown, the E-region ionization has fallen considerably. I think E-region still probably continues to be the pertinent reflecting region because of the high latitude, radiation from non-solar sources, etc, but I’m not totally sure. Critical frequency would approximate the E-region plasma frequency. E-region plasma frequency falls fast after sundown because it is proportional to ionization. A first scenario would do Appleton-Hartree calculation or modeling assuming E-region plasma frequency is still above 475KHz for purposes of comparing the Appleton-Hartree modeling vs. XPQ’s actual receptions. Also, since the signals involved probably are relatively lower in elevation angle, the E-region MUF, which is about 3x the critical frequency would be well above 475KHz as well.
Now suppose the opposite–the E-region plasma frequency falls below 475KHz. In that case, F-region is the reflecting region because the E-region has became transparent to 630m after AK SS. Then you have 1-Fhop prop and one instance of skew at F-region altitude roughly 1500km west of WA and 1500km south of AK forming an angled path on a map if the incoming XGP RF is going to be at a south heading into XPQ.
Gyrofrequency is essential to Appleton-Hartree; it’s proportional to GMF strength and independent of all else. Subject to space weather and geomagnetic fluctuations, GMF is probably somewhat steady, and so gyrofrequency would be somewhat steady all night along the XGP-xpq path. GMF is also relatively high, 55 microTeslas in higher latitudes. https://www.ngdc.noaa.gov/geomag/WMM/DoDWMM.shtml (click total intensity map). The gyrofrequency for sky reflections into Anchorage is way above 475 KHz, per the following calculation:
Gyrofrequency (KHz) = 55 uT x 28 KHz/uT = 1540 KHz.
Consider how all that relates to O/X waves and what 3D GMF direction pertains at 600-1500km S of Anchorage. There, GMF declination in the ionosphere would be about +18° from true North and inclined ~70° downward (20° away from straight down).
http://jeb.biologists.org/content/218/2/206 (Fig. 3, scroll halfway down). https://en.wikipedia.org/wiki/File:World_Magnetic_Inclination_2015.pdf
The direction of a near-horizontal RF ray along WA-AK great circle would be nearly perpendicular to the GMF, so there’s angle θ ~ 90° between the RF ray and GMF all the way. (The direction of near-horizontal skewed RF ray incoming to AK from the south would depart somewhat more from the perpendicular to GMF.) On the skewed path, westwardly departing from a great circle from Washington state, the 630m RF ray would then skew or turn its heading within 600-1500km of XPQ to make the omni outperform the loop.
If you use a propagation modeling software package, use one that includes GMF in the calculations and models MF/LF frequencies. It could help to rough out what’s going on.
In a future blog post let’s see how insights from this skew discussion may be used in Appleton-Hartree estimations.”
Additions, corrections, clarifications, etc? Send me a message on the Contact page or directly to KB5NJD gmail dot (com)!