I won’t lie – I am beginning to become a bit stir crazy from the current weather QRT here in Texas. Assuming the antenna is standing after tonight’s “main event” and the weather forecasters are correct , I look forward to be transmitting again tomorrow night. It seems like I may not have missed too much, however. Phil, VE3CIQ, notes that his range is shrinking, referring to fewer distant stations reporting him. He decoded three stations during the session while being decoded by eleven. It probably has more to do with the noise and stations missing for a variety of reasons. Lets hope that the great late season conditions return for a little while longer.
Geomagnetic activity was has been low again, although there was an M6.7 flare yesterday with a type II radio emission. If the ionosphere were upset by X-ray activity it is certainly plausible that some of the overnight conditions could see some latent effects from the daylight activity. The Bz is currently pointing to the North and solar wind velocities are low, below 400 km/s. A proton spike was observed during the daylight hours of the session.
Jeff, VE3EFF, is currently preparing his station for operation on 630-meters. The plan is to use a U3 at 1-watt TPO to a vertical loaded with a bucket coil of approximately 900 uH and a rotating coil of 48 uH. Thanks to Phil, VE3CIQ, for providing a picture and information about the impending operation.
Neil, W0YSE/7 / WG2XSV, made a startling discovery this morning when reviewing his data. It seems he experienced a major gap in reports. Further investigation suggests a time problem with his Dimension4 software. Larry, W7IUV / WH2XGP, reports a better tool that is more compatible with newer operating systems can be found at www.timesynctool.com. Neil provided the following comments from the session.
Mike, WA3TTS, experienced an improvement on the path to WH2XCR. Perhaps these reports are the result of the Northwest-facing EWE which was broadside to the southern storm QRN.
Larry, W7IUV / WH2XGP, reports a poor session, decoding only four WSPR stations and being decoded by 24 unique stations including VK4YB and VK2DDI.
Two new WSPR receive stations were observed during this session: W2LMM and WB2YDS. Welcome aboard.
Regional and continental WSPR breakdowns follow:
There were no reports from the trans-African or trans-Atlantic paths. UA0SNV was present from Asiatic Russia but no reports were found in the WSPRnet database.
Eden, ZF1EJ, provided reports for WH2XZO and WG2XXM on a noisy night.
Laurence, KL7L / WE2XPQ, operated transceive from Alaska and receive-only as KL7L/KH6. He reported WE2XPQ, VK3ELV and VK4YB from his portable location while WE2XPQ experienced poor conditions for the session in Alaska. Laurence included notes about his activity including a picture of the path to Australia.
Merv, K9FD/KH6 / WH2XCR, continues to see two-way reports from VK3ELV and VK4YB with reception reports from VK2XGJ and VK2DDI. VK7TW returned to reporting Merv during this session, which has not occurred since earlier in the season. Mike, WA3TTS, had the sole reports from the eastern US during this session, as previously reported.
In Australia, Phil, VK3ELV, and Roger, VK4YB, continue to experience two-way reports with WH2XCR. Phil received additional reports from JA-stations from this session as well as late reports from the previous session.
Jim, W5EST, begins a series of discussions entitled, “PART 1: DISPLACEMENT CURRENT AND YOUR 630M TRANSMITTING ANTENNA”:
“Displacement current can seem a mysterious concept. Even if you’re familiar with it, perhaps one more person’s outlook can interact with your own perspective.
In a capacitor, when current flows some charge onto one conductor and out the other, no actual electric current flows between the oppositely charged conductors (unless it sparks over). Instead, the flow of current increases or decreases the strength of an electric field between the conductors. The field is pictured by lines of force. Electric field strength, roughly speaking, relates to the voltage V across the capacitor divided by the distance d between oppositely charged conductors.
In the 19th century it was discovered that electric current makes a magnetic field H having a magnetic field strength proportional to the current. Later it was learned that the rate at which an electric field changes also creates a magnetic field having magnetic field strength proportional to it as well. So people continue to use the term displacement current instead of the clumsy phrase “equivalent current proportional to the rate at which an electric field changes.” For some history, see https://en.wikipedia.org/wiki/Displacement_current
Excitation at frequency f=475 KHz makes the electric field change in the antenna capacitance of your 630m antenna. The displacement current represented by the changing electric field in the antenna capacitance is approximately 2πf 8.85 (pF/meter) V/d. Put another way, amount of displacement current comes from multiplying voltage by capacitive susceptance (i.e., dividing voltage by capacitive reactance).
At 630m, 2πf is about 3 million (3×106/sec). So displacement current density at 630m is about 26.6 uF/meter times V/d. For every 1 KV of voltage per meter at 630m, you get roughly 26 mA/sq-meter of displacement current density. That’s because uF/meter (microfarads/meter) times 1000 volts/meter = milliamperes per sq-meter. Just as antenna current scales with frequency, so also there’s more displacement current density per KV at 160m and less displacement current density per KV at 2200m.
Now consider a 630m vertical antenna 20m tall, having 110 pF antenna capacitance, driven by a 630m transmitter and ATU to have 3A RF current and 13KV antenna voltage. (That was an example I blogged Jan. 15.) Let’s do some back-of-envelope numbers. The electric lines of force from the 20m-high vertical antenna curve toward the ground a short distance from its base and a long distance from its top. From its middle, the lines of force traverse a medium distance, roughly an arclength let us say of 18m. That makes a rough medium displacement current density amount something like 26 uF/m x 13KV / 18m ~= 19 mA/sq-meter. The displacement current density is greater near the base of the antenna and it’s less at the top.
How much total displacement current does the antenna have? Exactly as much as its 3A RF current! (Because of the basic connection of both types of currents to magnetic field strength, physicists have arranged the definitions and the constant 8.85 pF/m to deliver this equality.)
Imagine partway up the height of the vertical that the displacement current showers radially outward from the vertical down through a horizontal imaginary circle say about 14m wide encompassing like a necklace most of the displacement current. Then multiply the average displacement current density by the area πr2 of that imaginary circle. You get about 3A RF current: 19 mA/sq-meter x π (~7 meters)2 ~= 3A.
Think of the currents in a 630 m vertical antenna like the water in a water sprinkler that makes a very fine spray. The water goes up inside the skin of a vertical tube. From the tube, the spray goes out in all directions and curves in a shower toward the ground from every point on the surface of the tube all along the way up the vertical tube. The water in the tube is the 3A of RF current that goes up. The water in the spray is the displacement current that arcs downward.
Suppose you imagine luminous water in the tube and you “look” at the antenna from a distance. Then the antenna looks like a brilliant vertical line of light in a veil of luminous spray. That’s your 630m vertical antenna!
Now add a top hat to the picture. Displacement current spray still emanates from the vertical antenna section. Additionally, displacement current spray emanates sideways from the length of the top hat as well as off the end(s) of the top hat. A top hat makes the RF amperes of antenna current more uniform all the way up the vertical section (April 2, 3, 4, this blog). That way the antenna transmits more RF signal.
OK, but what difference does knowing about displacement current specifically make as we design and build our antennas and do our day-to-day LF/MF operations? Displacement current distribution means that antenna current and charge distributions aren’t the whole story of the electrical and magnetic energy storage properties of your antennas. Stray capacitances and intended capacitances are more easily estimated, planned for, and adjusted with displacement current in mind. Displacement current helps you understand how mini-whips and other receiving antennas work. Considering displacement current distribution also aids our experienced common sense assessing effects of 630m transmit antenna placement relative to towers, wire antennas, gutters, metal sheds, etc.
In further blog posts, let’s say more. Tell us what you think. Do you have some helpful analogies or tips to aid common sense understanding of antenna principles. Let us know so we can blog them!”
Additions, corrections, clarifications, etc? Send me a message on the Contact page or directly to KB5NJD <at> gmail dot (com)!