It really was looking like a reasonably good session before sunset here in Texas. Noise was relatively low, lower than seen in previous sessions, but as terrestrial storms began to ramp up and advance toward their targets, band conditions began to suffer. By 0700z the storms surrounded my station and the receive antennas were useless. Approaching storms in Texas meant a weather stoppage and no CW sked at 1030z. Storms are rampant here this morning as I develop this report. I am sure this story repeated itself over night for many stations on 630-meters across North America and around the world.
Geomagnetic activity spiked to storm levels with a south-pointing Bz, elevated solar wind above 400 km/s, and elevated protons. DST took a dive at most measurement points.
Phil, VE3CIQ, was impacted by noise during the session but notes that Jeff, VE3EFF, made his maiden voyage during this session at 0 dBm ERP to a short vertical. Phil decoded two more stations than I did over this session and offers the following details:
Neil, W0YSE/7 / WG2XSV, asks the question that is the elephant in the room this morning and offers this report of the session, including an observation of a new receiving station:
Terry, W8ARE / WI2XHK, recently made his maiden test voyage from his condo in Ohio using a 40-meter vertical retrofitted with toploading, base loading, and matching. Using approximately 35-watts from his amplifier, Terry estimates that he is radiating near 100-milliwatt ERP. Did I mention Terry lives in a condo with an HOA? Shortly his antenna will be relocated to the woods behind his home after being heavily disguised with paint. Terry has done a very nice job with his installation and should give hope to anyone that thinks they cannot operate from an HOA. Terry provided a few pictures showing his system and antenna locations:
Ron, NI7J / WH2XND, has been working on a compact dipole solution for stations that might suffer from a lack of space. Ron provided the following recent pictures of his creation, which is adjusted via a motorized variometer:
David, N1EA, posted the following question on the 600-meter research group:
It was followed by this response from Warren, K2ORS:
Recently, John, WA3ETD / WG2XKA, did some work with a loop stick and found the expected very sharp nulls and bidirectional pattern. John reported that the testing was inconclusive, however, and really needed a rotator and some elevation, both of which he would investigate in the future. The idea of off-center winding to achieve single direction response is interesting and I hope that John will consider this approach in his further testing. I have always been amazed at the performance of the loop stick.
Regional and continental WSPR breakdowns follow:
There were no reports from the trans-African path.
Luis, EA5DOM, received the sole trans-Atlantic report from WE2XGR/3.
Laurence, KL7L / WE2XPQ, reports that wildlife had impacted his transmit antenna top loading in Alaska while away but after making repairs and adjusting the system matching, he is back on the air. Unfortunately the high latitude aurora complicated his activities during this session. The path to Hawaii and British Columbia were open, however, as both paths are over salt water.
Merv, K9FD/KH6 / WH2XCR, was competing with lightning off the eastern coast of Australia during this session but was received by Roger, VK4YB through a very challenging session. The path to North America continues with all reporting stations at higher latitudes during this session and reports limited to the western portions of North America plus Alaska.
In Australia, Phil, VK3ELV, and Roger, VK4YB, were both reported in Hawaii by WH2XCR. Roger exchanged two-way reports with Merv and Phil received reports late in the previous session and early in this session from JH3XCU and JA8SCD5 from the previous session.
Jim, W5EST, relates today’s discussion to the system of Pat, W5THT / WD2XSH/6, and provides the following analysis entitled, “DESIGNER DISPLACEMENT CURRENT? TOP LOADING COILS FOR TOP HAT”:
“Today I continue the discussion of a 630m top hat from a displacement current point of view. If a top hat already somewhat migrates displacement current outward from a base-driven vertical, why not move even more by putting some of the loading inductance part way or all the way up the vertical? This blog (Jan. 18) described a loading arrangement by Pat WD2XSH/6 shown on http://500kc.com/about_stations/6/index.htm (next-to-last photo there).
So, I ask, wouldn’t that approach make the current in the vertical more uniform by reducing the kilovolts there that make displacement current spray out? (For displacement current basics, see this blog April 19.) If there’s less displacement current in the vertical, then it could push more displacement current out onto the top hat end to spray to the ground from there. That way, the electric field E of the top hat can get more nearly synchronized with the magnetic field H produced by the vertical and launch more RF signal (this blog, April 22-23).
To see if the radiation resistance can improve, let’s make EZ-NEC Demo revise the antenna model for end-arrow hatted antenna “F” (April 25-26, this blog). Move ATU inductance up so half of it is underneath the top hat 50’ up, and make half lie near the arrow-end.
The first illustration shows revised antenna “F” in the modeling windows. By trial and error, I put 400uH loading at the top of the vertical and another 400uH loading near the top hat’s end-arrow. The radiation resistance rises 64%, a factor 1.64 or 2dB, from unloaded original impedance 0.807-j594Ω to 1.321+j1646Ω with loading inductances, zero wire loss and perfect ground. The Rr improvement supports the idea that loading inductance can rearrange a 630m antenna E-field in a way that promotes more radiation, even with electrically short antenna “F” in its 70’ square footprint.
Remarkably also, the RF current distribution upward along the vertical actually stays the same or even gets more intense than at the base! Some displacement current is rising from the nearby ground into the vertical. I believe it’s because of a flywheel effect of the loading interacting with the antenna capacitances on either side. Displacement current descends to the ground farther out at the arrow-end of the top hat.
Compared to unloaded original arrow-hat inverted-L antenna “F”, adding inductance to load the end-arrow likely will increase the overall ground system resistance because more ground current will originate farther out from the vertical. In the April 28 example, 25.1Ω ground resistance was allocable to the top hat and 25Ω to the vertical. The sum 50.1Ω probably approximates the overall system ground resistance for the loaded antenna “F” here. Relative to the combined 42Ω for that example, this modified antenna “F” could probably suffer a ground resistance increase of: 50.1Ω/42Ω = 1.19.
Compared to the 1.64 multiplication of radiation resistance, the 1.19 increase in ground resistance still yields increased antenna efficiency because:
1.64 / 1.19 = 1.38 or 1.4dB.
If you’re willing to match to 75Ω instead of 50Ω, the 2nd illustration shows favorable antenna performance hugging 75Ω from 474.5 to 477 KHz with copper wire loss and real ground 5 mS/meter. The EZ-NEC source is coupled to a trivial L-network having just a low-voltage series variable capacitor set to 204 pF to cancel leftover inductive reactance of loaded antenna “F.” EZ-NEC ground resistance 25.1Ω for hat is series-entered with the 400uH at 90% out along the top hat. Ground resistance 25Ω near and beneath the vertical is series entered as Load 3 as if 10% up Wire 1.
Is this antenna improvement worth it? The inconvenience of getting two 400 uH coils 50’ up and keeping them suspended in the face of probable storm wind forces may be offset by a light-weight streamlined coil enclosure of low-loss material. Higher antenna efficiency 1.4 dB means less transmit power needed to attain a given EIRP.
I think two features merit particular interest. First, loading inductance can reduce displacement current leakage from the vertical into a nearby HF beam tower, or can attract displacement current from the tower to add to the antenna current. AC ground wiring in a house forms a conductor cage 20-30’ high. 630m displacement current from top hat midsection to a home AC cage underneath can be reduced by inductively loading the top hat of antenna “F.” The 2nd illustration shows this because the current distribution is made uniform along the 100’ top hat conductor.
Second, the top hat loading inductance can drastically reduce RF voltage on the vertical and much of the top hat without reducing RF current. Most of the risk of arcing is transferred to the end-arrow conductors where their more remote physical location can make that risk more manageable.
If you touch the low-voltage vertical section of loaded antenna “F”, it would probably still be “RF hot.” Even if “low voltage” means less than 1 KV, that’s still possibly several hundred volts of RF—but much more like usual RF risks hams plan for and manage at HF.
Nothing in this 630m game comes as easily or simply as we hope it will, does it. I hope this example at least shows that vertical antenna RF current can actually increase upward, that we can intentionally transfer displacement current to where we want it and control its leakage, and that vertical RF current of 1-2A does not inherently demand immense RF voltages on the vertical conductor near ground level. If these ideas encourage someone else to make this or some other 630m antenna work better or easier to construct, especially in small spaces, that’s the main thing.
Comments? Tell us your experiences and wisdom!”
Additions, corrections, clarifications, etc? Send me a message on the Contact page or directly to KB5NJD <at> gmail dot (com)!