Band conditions were slightly better overnight as Midwest and southern US storms were fewer in number and seemed to diminish as the session progressed. Yesterday Phil, VE3CIQ, reported a significant change in lightning noise as sunrise approached and the early morning progressed. I observed this same behavior this morning during my morning CW sked. The start of the sked was characterized by very high noise levels that was managed by using one of the directional receive antennas. By the end of the sked at 1100z, the noise was mostly gone. The Midwest storms were in sun at this point and suggests that the noise was no longer being propagated. Of course all of this is “textbook” band behavior and common sense analysis but it is interesting to see it in practice.
Geomagnetic conditions were quiet but continue to be elevated through the session. The Bz pointed generally to the North and solar wind velocities were elevated above 400 km/s.
Phil, VE3CIQ, reported a “better session than last, one bogus call Hearing: 376YKU, WG2XIQ, WG2XKA, WG2XXM, WI2XFI Heard by: SWL/K9, VE2PEP, WA3TTS/2, WD2XSH/17, WE2XGR/3, WG2XJM, WG2XKA, WI2XFI”
Ken, K5DNL / WG2XXM, reported that he decoded five WSPR stations including WI2XFI who was operating at 200 mW ERP at a distance of 1354 km. Ken was decoded by 27 unique stations including WE2XPQ at a distance of 4636km.
Neil, W0YSE/7 / WG2XSV, provided the following statistics for his session:
Regional and continental WSPR breakdowns follow:
There were no reports from the trans-Atlantic or trans-African path. UA0SNV and UA0SNV-1 were active from Asiatic Russia but no reports were found in the WSPRnet database.
Eden, ZF1EJ, decoded a few more WSPR stations during the session, including WG2XKA in Vermont.
Laurence, KL7L / WE2XPQ, reports co-channel activity for WE2XPQ during the session with a station in VK and transitioned to receive-only at 0722z after observing seasonal antenna tuning variations. Laurence continues to remotely control his station from Maui while on work assignment. WE2XPQ reported stations in the Pacific Northwest, Hawaii, and WG2XXM in Oklahoma. KL7L/KH6 continues to hear well, reporting WH2XGP, VK3ELV, and VK4YB.
Merv, K9FD/KH6 / WH2XCR, continues to see strong, early numbers from Australia as well as two-way reports with VK3ELV and VK4YB. John, VK2XGJ, persistently reports Merv’s signal at sunset, which is getting earlier each day. The band performance in Hawaii is rather fascinating and has really improved over the last year as activity in Oceania and Asia have increased significantly. Merv provided a few comments on the season as well as comparisons with 160-meters:
In Australia, activity as well as discussions about activity have increased significantly. Its seems the transition from Summer to Autumn and ultimately to Winterin the coming months in the southern hemisphere has had a positive effect on the number of active stations in Australia and its my hope that this activity will spread to New Zealand and surrounding areas.
Cliff, VK2NP, reports very conditions and submitted the following comments to the VK 600-meter email reflector:
David, VK2DDI, reports that he decoded a new station using a U3 at less than 1-watt TPO and a rain gutter for an antenna with no resonating or matching:
Brian, VK6LO, has recently equipped his station to decode WSPR signals from VK6 and submitted these statistics for his session:
Today’s discussion from Jim, W5EST, is entitled, “ESTIMATE A RATIO OF 630M GROUNDING SYSTEM RESISTANCES”:
“Estimating the grounding system resistance for even a hatless vertical is a challenging topic. Kudos to Rudy N6LF, who has studied an example of 630m short vertical 50’ tall with a parasol-shaped top hat and a dense 25’ radial system.* He explains frequency dependence of both the ground conductivity and the ground’s dielectric constant ε. His work invites careful reading by us all.
In the last few days’ blogs, I’ve offered modeling data on favorable 630m antenna geometries with top hats that extend horizontally by lengths exceeding the vertical’s height. If and when 630m is approved by FCC for US amateurs, prospective 630m ham operators might find it inconvenient or uneconomical to provide a radial system beneath a vertical with an extended top hat.
Hams may already have put in some ground rods, or would be willing to do so, near the antenna base. But they may prefer to omit radials if possible. They could decide to drive their 630m antenna harder with sufficient transmit power TPO to reach some desired EIRP within a legal limit.
If you can put in radials, do so. Unconventional and foolish as even considering the idea of few or no radials may seem, however, the prospect of building big radial fields may deter some hams from 630, even though Part 5 stations install them.
The question of overall ground system resistance only enters the calculations that I blogged yesterday after maximum RF amperes have already been estimated. From a prospective station operator’s viewpoint, if TPO can be adjusted sufficiently to set the RF amperes of the antenna current to a desired value, then addressing ground system resistance diminishes in importance.
I assert that the ground system resistance question is unavoidable when comparing different 630m antenna designs. Would a proposed top hat design deliver 20% more radiation resistance than another design, but entail 20% more ground system resistance? If so, the proposed design may be no improvement, especially if it’s more complex to construct.
Accordingly, I offer some thoughts about relative ground system resistance mostly for comparing antenna designs. It’s the ratios that especially matter for antenna comparisons, and not the exact values as much. I hope this post encourages work on some simple formulas for ground system resistance ratio of vertical with extended top hat compared to ground system resistance of vertical alone. That way, hard-to-determine values of ground conductivity and depth of RF ground current penetration cancel out.
A top hat makes the RF current distributed upward along the vertical height more nearly equal to the RF current driven to the antenna base. A top hat can double or triple the radiated power for a given antenna base RF current. However, the top hat does this by migrating displacement current away from the vertical over to the top hat farther out. See illustration. There, the displacement current enters the ground beneath the top hat and continues as RF ground current. More ground resistance is inevitable—because of more length that the ground current has to travel back from the top hat to the drive point near the antenna base. That’s the bad news.
However, good news continues this story, I believe. The extra ground resistance from the top hat back to the drive point doesn’t affect the system ground resistance as much as one might think. Consider an example figured below and shown in the illustration. I’ve set up some of the numbers after referring to the EZ-NEC demo modeling April 26, this blog.
Suppose the ground system has ground rod(s) and no radials. Let an example value be 25Ω for ground system resistance of a circular area of earth out to about 50’ from a hatless vertical. Arbitrarily set the antenna base RF current to 2.83A rms, so the I2R power dissipated in the ground resistance is 200 watts.
In the modeling, keep also in mind that the illustrated top-hatted vertical “F” showed radiation resistance 0.80Ω compared to 0.24Ω for the hatless vertical “A.” That ratio is 3.33 in favor of antenna “F.”
Now consider the top hat for antenna “F” that sinks most of the displacement current that otherwise would have descended from the vertical. It leaves the vertical spraying what’s left: 17%.
You get the vertical’s 17% fraction of displacement current (shown light green) for antenna “F” from the reactances reported by the model:
kV&Hat = X V&Hat /Xhatless = -j612Ω/-j3482Ω = 0.176.
By comparison, a hatless vertical sprays 100% of its RF current as displacement current, kV =1.0. Radiation resistance is directly related to radiated power, so both radiated power and Rradiation will go up by a factor 3.33. You also get 3.33 from (1 – 0.176/2)2/(1- 1.0/2)2 , which expresses the improvement in squared average current along the vertical’s height.
Let 25.1Ω be the example value of average ground resistance beneath and along the top hat back to the edge of that 50’ radius circle around the vertical. (I’ve deliberately put 25.1 there so that today’s example can be read together with yesterday’s example.) Roughly what will be the overall system ground resistance now, compared to 25.1Ω? Mustn’t it be the sum 50.1Ω because the resistances are in series? NO!
Imagine a measurement process— one you don’t need to actually do. With top hat added, a fictitious ATU is re-resonated and antenna base current adjusted as if to restore the original 2.83A RF amperes base current. With this hat model, 82.4% of that 2.83A goes out onto the hat, and down as hat displacement current (light orange). It returns as 2.33A ground current through 25.1Ω hat-related ground resistance, which dissipates 136 watts, or (2.33A)225.1Ω.
Meanwhile, that 82.4% ground current from the hat reaches the vicinity of the vertical. There, it combines with the other 17.6% displacement current from the vertical. The combined current, the entire original 2.83A, returns to the drive point and still dissipates about 200 watts in the 25Ω ground resistance associated with the vertical. The total dissipated power 336 watts, dissipated in the ground everywhere, includes hat’s 136 watts. The overall ground resistance seen from the drive point is then found to be:
Rgnd = P/I2 = 336 watts/(2.83A)2 = 42Ω. (Not 50.1Ω!)
Compared to the hatless vertical, the increase in ground system resistance in this particular example is
42Ω/25Ω = 1.68.
Compared to the 3.33 multiplication of radiation resistance, the unfortunate 1.68 increase in ground resistance still leaves doubled antenna efficiency because:
3.33/1.68 = 1.98.
Higher antenna efficiency means less transmit power TPO required, 101 watts or 200 watts/1.98, which translates to the 1.56A rms of yesterday’s calculation to get the same radiated power as the RF current into a hatless vertical.
This is, of course, merely an example. I offer it because it illustrates a more general principle that overall ground system resistance with a top hat does not combine by simple addition of ground resistance under the hat with ground resistance near a hatless vertical. Moreover, the top hat ground resistance can be kept manageable by arranging for top hat T-ends or arrow ends to constrain the top hat distance from the vertical and still maintain high radiation resistance. See the footprint diagram of one such antenna in the illustration.
*Severns, R. “Radiation and Ground Loss Resistances In LF, MF and HF Verticals; Part 2.” QEX Sept./Oct. 2015:27-28. Also click: “Rr study appendix B Soil characteristics at MF and HF.” http://www.antennasbyn6lf.com/design_of_radial_ground_systems/“
Note that much of the previous content from Jim that is posted daily in this blog is also being added to the 630m.net site where topics stand alone and may be easier to search in the future as this blog continues to grow.
Additions, corrections, clarifications, etc? Send me a message on the Contact page or directly to KB5NJD <at> gmail dot (com)!