So it was another noisy night, not out of character for this time of year, and several stations continued to be QRT for a number of reasons. WG2XXM reported yesterday after sunrise that he had taken a lightning hit at his station around 0930z, damaging multiple PC’s, a K3, and other hardware necessary for accessing the Internet. Lightning strikes can happen to any of us at any time and this is just a reminder of how quickly things can change. From the sound of it, there were no injuries and the house was not burned down but I feel certain that setbacks like this are especially tough after so much work has been done to put together an effective station. Our thoughts and prayers are with Ken as he works out a strategy to recover from this disaster.
The bands don’t seem to have been particularly poor, no more so than recently seen. It seems that stations with some receive directivity were able to find some success which was secondary to just being brave enough to be on the air with the number of storms that were active. There is no shame in being QRT for bad weather. Keep it safe – always!
Geomagnetic conditions were quiet. The Bz was variable, currently pointing slightly to the South. Solar wind velocities remain low, below 400 km/s. DST appears to have been optimal in both VK and JA for much of the overnight period.
Laurence, KL7L / WE2XPQ, reports that he is shutting down from his work assignment in KH6 and provided this picture of his operating conditions in his hotel room in Maui:
Mike, WA3TTS, reported this morning that Larry, W7IUV / WH2XGP, was “blasting through the QRN…”
Brian, VK6LO, submitted this report on the VK 600m email reflector:
Neil, W0YSE/7 / WG2XSV, reports a slow night on the continent but he still managed some WSPR reports.
Regional and continental WSPR breakdowns follow:
There were no reports from the trans-Atlantic or trans-African paths. UA0SNV/UA0SNV-1 and ZF1EJ were present but no reports were found in the WSPRnet database.
Laurence, KL7L / WE2XPQ, reported stations in the Pacific Northwest and Hawaii from Alaska while KL7L/KH6 made one final hurrah, reporting WH2XGP in Washington state with VK4YB and VK3ELV in Australia. Laurence experienced nice, consistent conditions from Hawaii which I am sure are more pleasing than some of his recent experiences in Alaska.
Merv, K9FD/KH6 / WH2XCR, was reported in Australia and continues to receive reports from there as well as Alaska and the western portions of North America. This session was not as good as previous and John, VK2XGJ, reports just a few smudges on the waterfall on an otherwise poor night.
In Australia, Roger, VK4YB, and Phil, VK3ELV, were reported by WH2XCR. Roger exchanged two-way reports with Merv and Phil received reports from this session and from late in the previous session from stations in Japan.
Jim, W5EST, goes to the mailbag once again, this time to examine the system at WG2XSV with this discussion entitled, “SOURCE MATCHING IN ANTENNA MODEL BY EZ-NEC DEMO”:
“Neil WG2XSV W0YSE e-mailed this information:
‘I have been modeling my antenna with EZnec Demo 6.0. The first attachment shows my Rr is 0.319 ohms (in the SWR graph) by putting a zero in the LOAD resistance (not the wire loss box of the main dialog box). I also did an SWR of the whole 630m band with a load resistance of 22 ohms, which I think is close to my total resistance also. Do you have any things to enlighten…’
Jim W5EST reply: The first illustration specifies aluminum conductor segments of a 40’-tall 1.5” diameter vertical over perfect ground with three 27’umbrella top hat conductors sloping 37° down from 40’ to 25’.
The top hat is improving uniformity of RF current up along the vertical (degree-amperes). Unfortunately, the top hat’s umbrella downslope is partially canceling radiation from the center vertical.
One can get a bit confused at first because the elevation pattern display indicates a “gain” of -15.6 dBi. By contrast, the actual antenna almost certainly delivers several dB gain over isotropic.
To confirm this, temporarily delete the load that was entered in EZ-NEC Demo and click the “SWR” button to rerun. You get antenna impedance 0.3184 – j1413 ohms. (That explains why XSV had entered X=1412 inductive reactance in the Load box beforehand.)
Without the load, the far field FF Plot for elevation pattern shows 4.03 dBi, a little less than short vertical 4.77dBi over isotropic because of wire loss in the aluminum wire.
So the $64 question is, “How then do I simulate a match in EZ-NEC and get a useful SWR plot?” Answer: In EZ-NEC Demo Help menu, click on “Building The Model” to then click on the subsection “Using L Networks.” That’s because WG2XSV has a T-network ATU shown in this blog March 22. Also, a loading coil alone will merely deliver the low-ohm antenna resistance itself (0.319Ω including Rradiation 0.272Ω) when you resonate the antenna. So the displayed SWR will be out of sight.
L-networks in EZ-NEC Demo have a series branch from port 1 and a shunt branch across port 2. Cascade a second L-network to make a T-network, or whatever network you want. In the “Config” cell, click and pull-down-choose “S” or “Ser” to put R,L,C all in series, “Par” for R,L,C all in parallel. When inserting RLC values, “0” in series means 0Ω. “0” in parallel omits the component. (If you don’t see cells for RLC values, click the “Other” option to change L-network type, choose the “RLC” button, and click “OK” to get them.)
Connect a 1 volt voltage source to a first L-network via virtual wire number, e.g. “V10.” Specify V10 both in the Source box and the first L-network input port. The first L-network I endowed with zero series resistance, 0 uH series inductance, and a 500 pF series capacitance. Pull-down-choose .4757 frequency and series configuration “Ser” in the “Config” cell.
Next comes the shunt output side of the first L-network. That’s the second row of cells. Specify/connect a virtual wire segment V20 to its output, and enter R=0, L=90 uH, C=0 (omit), .4757 and parallel “Par” in the “Config” cell.
To put in the loading coil (impedance autotransformer step-up side), go to “L Ntwk” menu and click “Add.” In a new cell-set, specify a cascade 2nd L-network. Virtual wire V20 goes to RLC 22Ω ground resistance, 323 uH, 0, .4757, Ser. The inductance values seemed rather critical, which corresponds to getting the actual coil taps right in reality. I put the ground resistance in series in the 2nd L-network because that’s equivalent to the ATU seeing the antenna in series with ground resistance.
How does one connect up the loading coil at port #2 to the antenna? In the Port 2 Wire # cell enter the antenna vertical base’s wire numeral one “1”. Specify zeroes in the 2nd L-network’s shunt side RLC = 0 0 0 .4757 and Par.
This way, a voltage source (your transmitter and coax) has been successfully connected to an ATU comprised of the XSV T-network. That T-network in EZ-NEC Demo was aggregated from two L-networks in cascade. The output side of the ATU goes to a model of the XSV antenna.
The “SWR” display shows ATU input impedance very close to 50Ω and predicted SWR less than 1.1 : 1 from 475.500 to 475.850 KHz. The SWR rises but stays less than 1.5 : 1 if you QSY down to 474.5 KHz. The antenna elevation pattern shows a typical zenith null, and its display reports “gain” of -14.42 dBi, which is not surprising because of the preponderant dissipation in the ground system resistance.
Antenna modeling software rewards your persistence, and I hope this discussion speeds along your modeling efforts. Physical results and RLC values will vary of course. Further blog posts can compare some antenna variations for 630m.”
Additions, corrections, clarifications, etc? Send me a message on the Contact page or directly to KB5NJD <at> gmail dot (com)!