Noise was elevated for a number of stations as the storm system that recently impacted the central US progressed to the East. As my first session back following the inclement weather, I was pleasantly surprised that the noise was not worse than it was here in Texas. Stations in the Midwest, such as WA9ETW and SWL/EN61, noted that the storms were challenging their ability to hear. Eric, NO3M / WG2XJM, was hearing very well as usual, reporting my signal at single-digit S/N numbers. Its always surprising how well Eric seems to hear through storms.
Geomagnetic conditions were quiet but elevated and the Bz pointed strongly to the North. Solar wind velocities were elevated above 400 km/s into the moderate range and proton levels were elevated during the late afternoon and into the evening once again. Unsettled to storm conditions are expected in the coming days.
John, WA3ETD / WG2XKA, reports that the band must have been very good overnight as he was decoded by VE7SL and my station here in Texas. Additionally John has been working on an interesting receive antenna at this station and reports that it is a work in progress with room for improvement, particularly with the input match to the preamp. He provides details below:
Neil, W0YSE/7 / WG2XSV, reports that he has reworked his amplifier to allow better heat conduction from his FET to the heat sink while providing improved RF shielding. The amp performed well overnight. Neil noted this morning that heavy rain caused him to stop transmitting at 0702z. He provided the following statistics for the session:
Mark, WA9ETW / WI2XHJ, reports high but not terrible noise levels as storms progress through his region. He notes decodes of WH2XZO, WH2XXM, WE2XGR/3, and WG2XIQ before securing his station for the evening at 0251z.
Steve, VE7SL, reports the he decoded eleven WSPR stations using the 10-foot by 20-foot loop oriented to Australia. This antenna has the added benefit of providing cover to the US/Canadian border to the East, while nulling strong signals to the south-southeast and Alaska.
Phil, VE3CIQ, reports that he decoded five WSPR stations and was decoded by eleven unique stations with WG2XXM and WG2XIQ being the best DX. Phil notes lightning crashes but local noise was down.
Ken, K5DNL / WG2XXM, reports that he decoded nine WSPR stations, including WH2XCR and VE3CNF. Ken was decoded by 33 unique stations, including KL7L/KH6 and WE2XPQ. He was also reported 61 times by Steve, VE7SL, with a best report at +4 dB S/N at a distance of 2610km. Ken notes relatively low QRN conditions from Oklahoma which resulted in nine decodes of WH2XCR with a best of -18 dB S/N.
The other Ken, SWL-K9, in Indiana used a little engineering skill so he would not miss the session due to thunderstorms. His efforts paid off with a few big reports. Ken explains:
WSPR activity was relatively high for this time of year, with 67 MF WSPR stations observed at 0300z. KK6NON was observed receiving during the session and while the call sign sounds familiar to me, no references are found suggesting that this station has reported on 630-meter WSPR in the past. Welcome aboard!
Regional and continental WSPR breakdowns follow:
There were no reports from the trans-Atlantic or trans-African paths. UA0SNV was present from Asiatic Russia but no reports were found in the WSPRnet database. No stations were present from the Cayman Islands during this session.
Laurence, KL7L / WE2XPQ, made a very strong showing from Alaska and Hawaii, reporting VK4YB and WG2XXM as previously reported. KL7L/KH6 additionally reported VK3ELV and continues to operate in a receive-only capacity as Laurence is working in Hawaii.
Merv, K9FD/KH6 / WH2XCR, experienced a typical, strong session with two-way reports at VK4YB. John, VK2XGJ, reported thunderstorms in his area and did not expect to decode Merv but it appears that a reception was recorded. VK3ELV was also reported by Merv during the session. WG2XJM and SWL/K9 (SWL/EN61) was were the easternmost stations to receive Merv’s signal.
In Australia, Phil, VK3ELV, received a reception report from WH2XCR while Roger, VK4YB, continues his streak of two-way reports with Merv. Phil received a few additional reports from JH3XCU during this session.
Jim, W5EST, continues his current discussion, entitled, “PART 4: HOW THE ANTENNA’S NEAR FIELD LAUNCHES YOUR RADIATED SIGNAL”:
“Since your TX vertical antenna is probably electrically small, 20m (66′) or less, how do those near fields get out to 200 meters away to launch RF? How are the propagating radio waves of your RF signal launched anyway? What’s in this mysterious near field? This subject is a bit like when a child asks how babies happen. A child knows that babies get born and that at least Mommie has something to do with it. Beyond that, the conversation may trail off.
Here’s one approach to an answer—on the topic of RF launch, that is. The antenna fields E and H need to match the 377Ω intrinsic impedance of free space. That’s not a simple thing. Fortunately in the near field, the E and H fields at a given point are already perpendicular, which is a first requirement. Electric fields in an isolated vertical antenna lie in vertical planes passing through the vertical. The magnetic fields encircle the antenna horizontally.
Additionally, however, E and H fields have to be in phase, which is another way of saying that some of the displacement current has to act like a lamination of current a significant fraction of a wavelength nearer the antenna than at least some of the H field. That way, they will be able to regenerate each other farther out and propagate outward. On top of that, E and H need to be in the right ratio to match the 377Ω characteristic impedance of air and free space.
If E/H departs considerably from 377Ω, RF power simply boomerangs back to the antenna. Insofar as portions of electric field E and magnetic intensity H do get in the right ratio and in phase, those portions will continue to propagate and will get launched by your antenna.
Very close to the antenna, in a non-radiative portion of the near field, the strong magnetic field H is in phase with the vertical RF base current I that generates it. Meanwhile, the strong electric field E due to the capacitance of the antenna is 90° out of phase with that RF base current I. These close-in magnetic and electric fields are not in phase and lack significant spatial separation because they largely intersect. Consequently, they do not support radiation regardless of whether they have the right ratio of magnitudes.
Farther away, E/H approaches not only the in-phase condition but also the right ratio E/H =377Ω ohms in an outer part (Fresnel zone) of the near field and beyond. https://en.wikipedia.org/wiki/Electromagnetic_radiation
Most energy in the electric and magnetic near fields of the antenna is poorly coupled to the 377Ω impedance of free space. That energy simply reflects back into the antenna and to the loading coil of the ATU.
With all that in mind, coupling to 377Ω can occur at a radius r from the MF/LF vertical antenna in a radiative zone. Not far into the radiative zone of distance, the match of the fields to 377Ω is about 6:1 “SWR” relative to free space, not very good. But the “SWR” gets more and more favorable with increasing distance r.
By the way, the term “SWR” is not generally used to describe the coupling of an antenna to free space, but SWR generally does have meaning to us experimenters and radio amateurs. In a radiative way of using “SWR” here, we are looking for distances out from the antenna that deliver in-phase E/H roughly in a range 75Ω to 377Ω without being very reactive. This “SWR” has nothing to do with the match to the ATU nor the ATU match to the coax from your shack.
I’ve been digging into antenna field equations and their near-field solutions. My calculations indicate that, relative to free space, an electrically-short vertical antenna at about one-ninth wavelength (λ/9, 70 meters or 220 feet out) looks like a very low impedance, very-high-“SWR” source with significant capacitive reactance. Almost all the real RF power in the fields there is incapable of coupling to free space 377Ω.
At one-sixth wavelength (λ/6, 105 meters or 350 feet out), however, about half the power in the RF fields there is coupled into free space as if “SWR” were considerable. Farther out, moreover, RF signal launch conditions become really favorable at and beyond one-third wavelength (λ/3, 210 meters or 700 feet out). There, the “SWR” referenced to free space falls to 1.5:1 or less, and the amount of power delivered into radiation out of the fields there rises above 95%. That’s the good news. The bad news is only a small portion of the energy in the MF/LF antenna fields lies that far distant.
An amateur’s HF quarter-wave vertical is already about λ/4 tall. Its radiation emerges from the surroundings right by it. By contrast, an electrically short MF/LF vertical is often no more than λ/32 and radiates from places that are 5-10 times as far away from the antenna as the antenna is tall. Close in, a big hemispheric ball of stored energy just shuttles in and out of the antenna between it and the ATU.
Structures like HF antennas, tower, metal shed and residential gutters mostly lie within the MF/LF antenna’s non-radiative zone where most of the energy of the MF/LF antenna is stored. So those other structures mostly attract displacement currents that divert from the MF/LF system some of its vertical antenna current. Those structures may shift the physical distribution of the ball of reactive energy in the antenna fields somewhat as well.
In conclusion, I hasten to emphasize that I’ve quite informally pictured your 630/2200m vertical TX antenna and its near field. The equations supporting this blog post are available on request. If you have better wisdom or a better way of describing antenna subjects, or a link to some good website, or some outright correction, e-mail us so we can post to this blog!”
Additions, corrections, clarifications, etc? Send me a message on the Contact page or directly to KB5NJD <at> gmail dot (com)!