The session was very quiet for many stations during the early portions of the session. Because of limited WSPR decodes early on I’m starting to wonder if the quiet conditions were the result of slow-to-start band openings and no propagation to regions where storms were raging. There were quite a few areas around North and Central America with lots of lightning and by the time of my morning CW sked the noise level was peaking at S9 but was remedied by using one of the other receive antennas. It was certainly louder than it was during the evening last night.
Geomagnetic conditions were quiet however the Bz was pointing to the South and solar wind velocities were elevated to the moderate category, above 400 km/s.
Ken, K5DNL / WG2XXM, reports that he decoded four WSPR stations during the session and notes QRN was present and likely impacting his hearing. He also notes that he was decoded by 31 unique stations during the session including VK2DDI.
Neil, W0YSE/7 / WG2XSV, reports cold weather and improved antenna base current. He provided the following comments and statistics for his session.
Larry. W7IUV / WH2XGP, reports that his WSPR software locked up around 0730z and he was subsequently absent after that time.
Doug, K4LY / WH2XZO, reports that he has been busy with his teaching schedule but plans a modification to his antenna system that will increase his antenna height and allow antennas below to rotate without getting tangled in top loading wires.
Phil, VE3CIQ, reports a slow session, decoding three WSPR stations and being decoded by “a whopping five” unique stations.
Al, W5LUA / WH2XES, reports that he has renewed his license and hopes to be more active this Fall, hopefully as W5LUA.
WSPR activity dominated as many stations transition to “auto-pilot” for the summer. 68 MF WSPR stations were observed at 0130z, however, so activity is still relatively high.
Regional and continental WSPR breakdowns follow:
There were no reports from the trans-Atlantic or trans-African path during this session. UA0SNV and UA0SNV-1 were present during the session but no reports were found in the WSPRnet database.
The Caribbean was well represented once again, with reports from Eden, ZF1EJ, and Roger, ZF1RC.
Stronger band conditions were in order in Alaska for Laurence, KL7L / WE2XPQ, with reports of WG2XXM in Oklahoma. KL7L/KH6 continues to have a nice opening to VK4YB and VK3ELV.
Post-sunrise reports for Merv, K9FD/KH6 / WH2XCR, continue in Hawaii. The band continues to perform well on the path to Australia and Tasmania in addition to Alaska and the US mainland.
In Australia, Phil, VK3ELV, and Roger, VK4YB, continue to receive reports from WH2XCR. Roger and Merv also exchanged two-way reports. Phil received additional reports from Japan, a few of which were from late in the previous session.
Jim, W5EST, presents a discussion entitled, “COMPARE 630M ANTENNAS WITH MODELING SOFTWARE”:
“Yesterday’s blog described how to set up a free antenna modeling program for different antenna geometries. Today let’s compare some of them.
Before I get started, though, the EZ-NEC demo apparently states antenna resistance as the resistive part of the antenna impedance when you click “SWR.” That antenna resistance value may include wire losses but importantly excludes the ground system resistance. I’ll get to that later.
The illustration shows four 630m antennas E, F, G, H overlaid on hypothetical property lots. All the antennas I discuss today are no more than 50’ high. In the TABLES Antennas A-D are provided for reference. Antennas E and H each occupy 100’ x 140’. Antenna F extends no more than 100’ diagonally and fits a 70’x70’ square footprint. Antenna G fits diagonally on a narrow deep lot encompassing a 70’x140’ footprint.
TABLE 1A lists various geometries using comparable total lengths of wires. Frequency is 475.700 KHz. For modeling, I’ve entered real ground conductivity 20 milliSiemens per meter with dielectric constant ε = 13.
TABLE 1B shows the modeling results for antenna impedance R+jX, respective gain over isotropic (dBi) for real ground and perfect ground, dB zenith-null depth, and f/b ratio. The four illustrated antennas E, F, G, H either outperform the reference antennas A-B or perform almost equal to reference antennas C-D at least twice their size that could not fit on the property lots shown. (For details, see endnotes*.)
TABLE 1A: ANTENNA GEOMETRIES
A 50’ vertical
B 50’ x 100’ inv-L
C 50’ x 240’ inv-L
D 50’ T-ant. with symmetric hat 240’ long (two 120’ halves)
E 50’ x 100’ & 140’ end-tee for inv-L hat (two 70’ end-tee halves)
F 50’ x 100’ & 2×70’ “arrow” 45° back (diagonal hat to arrow on property corner sides)
G 50’ x 100’ & 2×70’ oblique end-T (diagonal across to oblique T-end near lot line)
H 50’ x 100’ & 140’ end-L for inv-L hat (one 140’ full end)
ANTENNA IMPEDANCE INCLUDES RADIATION RESISTANCE (Wire Loss =0)
Geometry Impedance dBi dBi dB zenith Front/back ratio
Ohms 20mS/m Perf.Gnd @ 10° elev.
A 0.24 –j3482 3.61 4.77 -40 0 dB
B 0.67 –j1205 3.79 4.74 -15 0.4dB
C 0.86 –j 501 4.05 4.50 -7 1 dB
D 0.79 –j 639 3.65 4.77 -45 0 dB
E 0.83 –j 553 3.91 4.67 -11 0.7dB
F 0.80 –j 612 3.86 4.71 -13 0.5dB
G 0.82 –j 582 3.91 4.67 -11 0.7dB
H 0.84 –j 512 3.89 4.60 -10 0.8dB
RESULTS: Compared to antennas A and B with their shorter total length, antennas C-H all have less capacitive reactance and need less loading inductance. Lower inductance means lower Q, easier QSY on 630m, and less voltage multiplication KV on the wires, as discussed April 3, this blog.
Compared to each other, the five antennas C-H each have 50’ height and 240’ of top hat conductor length. They all have favorable radiation resistance 0.79-0.86 ohms for high overall radiative capability and less required transmit power TPO.
But these antennas C-H occupy different spaces and orientations on a person’s land property and perform somewhat differently. Antennas C and E-H may have somewhat higher performance on shorter one-hop paths because of their moderate zenith null that is less pronounced than vertical antenna A or symmetric 240’ top hat D.
Antennas E, F, G, H fit well in smaller properties because of their 100’ length and 140’ ends. Antenna G fits into a narrower property because of its 100’ diagonalized hat length. Antenna F can be installed or hung near a 70’x70′ property corner to reach its 70’ end-arrow hat perpendiculars at an opposite corner. Of these antennas E-H, antenna H calls for the least loading inductance and provides the highest radiation resistance among them.
Antenna efficiency involves the ratio of radiation resistance to total antenna system resistance including ground resistance. Ground resistance often far-outweighs the wire resistances in a 630m antenna system. The “Wire Loss” button in EZ-NEC can choose various wire compositions and add the wire resistance to give you a combined resistive part of the antenna impedance when you click “SWR.” That EZ-NEC antenna resistance value includes wire resistance but importantly excludes the ground system resistance.
Since I don’t see a menu item or output datum for ground system resistance in the EZ-NEC demo, let’s explore that topic in an upcoming blog post. Tomorrow, let’s estimate RF antenna current and figure TRP, EIRP and TPO. GL & 73!
*NOTES: Applicable setback requirements, zoning restrictions, neighborhood homeowner agreements, and informal visual requirements will vary.
The distribution of ground system radials may alter displacement current and E-field distribution modeled for uniform “real ground.” Put down several ground rods deep near the vertical antenna base. If radials are used at all, run them underneath and parallel to the entire top hat.
EZ-NEC divides the antenna into user-specified numbers of current segments. To avoid an error message, the total number of such segments must not exceed 20 in the free demo. Try specifying different combinations of numbers of segments for different wires to assess variation in the R+jX impedance output and the estimated dBi gain over real ground.
The modeling ignored possible displacement current leakage to any HF antennas, tower, gutters, nearby power lines, and phone and cable TV feeds, home electrical wiring, and metal garage or shed. Such modeling is useful and justifiable for comparative purposes. Displacement current may also induce 630m RF currents into those conductive structures, so be alert for RF interference from 630m antenna installation on small lots.
Intelligently separate 630m antenna conductors from any such structures to prevent 630m high antenna voltage from sparking over to them. Optionally put less loading inductance in the ATU and suspend the remaining inductance higher up to reduce and reposition the 630m antenna voltage.”
Additions, corrections, clarifications, etc? Send me a message on the Contact page or directly to KB5NJD <at> gmail dot (com)!