I am typically an optimist about this stuff but let’s face it – last night was pretty bad. Maybe it was the noise, maybe it was propagation, or maybe a few normally active stations were taking refuge from the bad weather. However you label it, the night was not very strong for many stations. There were a few bright spots, however. Larry, W7IUV / WH2XGP, was reported by VK4YB on a path that has been relatively forgiving for stations on the US mainland. Larry also noted that he decoded only two WSPR stations and was decoded by fifteen during what he classified as a poor session.
Merv, K9FD/KH6 / WH2XCR, also had a strong night with stations in Australia and Tasmania which will detailed later in this report.
Geomagnetic activity was technically quiet but elevated solar wind velocities above 450 km/s and a south-pointing Bz along with terrestrial noise just made the session miserable for those brave enough to operate.
Phil, VE3CIQ, notes that for “last night’s session, this is all I could squeeze out of it. Hearing: WE2XGR/3, WG2XKA, WH2XZO Heard by: SWL/K9, VE2PEP, WA3TTS/2, WD2XSH/17, WE2XGR/3, WG2XJM, WG2XKA, WI2XFI.”
Neil, W0YSE/7 / WG2XSV, provided the following statistics for this session from his location in the Pacific Northwest:
John, WA3ETD / WG2XKA, reports a below average session from Vermont as a heavy mist was in the air with wet foliage soaking up RF.
Mark, WA9ETW / WI2XHJ, noted that in two hours of reception last night he only had two decodes and both were from WH2XZO.
Ken, SWL/EN61, in Indiana also noted poor conditions and provided the following comments:
Laurence, KL7L / WE2XPQ, who has been receiving remotely while working in Hawaii, provided the following observations for his time in Maui as well as a graphic to show his location and obstructions that impact RF in a few directions on the US mainland.
Regional and continental WSPR breakdowns follow:
There were no trans-Atlantic or trans-African reports during this session. UA0SNV and UA0SNV-1 were active during the session but no reports were found in the WSPRnet database.
Eden, ZF1EJ, reports that the sole decode in the Caribbean was for WH2XZO in South Carolina.
In Alaska, Laurence, KL7L / WE2XPQ, reports that he was transmitting as WE2XPQ but no reports were found. It is unclear at the moment whether the system was on the air or band conditions were poor enough that no stations decoded Laurence’s signals. That is a rare occurrence. In Hawaii, KL7L/KH6, decoded VK4YB, VK3ELV, and WH2XGP as the only US mainland station. WH2XCR was also decoded at a range of approximately 100 km.
Merv, K9FD/KH6 / WH2XCR, continues to experience a strong path to Oceania with numerous reports from Australia and Tasmania. Two-way reports with VK3ELV and VK4YB continue. The West coast of North America and Alaska are also well represented.
In Australia, Phil, VK3ELV, and Roger, VK4YB, continue to exchange two-way reports with WH2XCR. Phil also received reports from JF1LKS and JF3XCU, some of which were from late in the previous session.
Jim, W5EST, provides this modeling-related discussion entitled, “ESTIMATE RF CURRENT, TRP, EIRP AND TPO FROM MODELING RESULTS”:
“Today, let’s show some important estimates you can derive from the output values from an antenna modeling program.
Recall inverted-L antenna “H” from yesterday’s blog. Its top hat features an extensive L-shape viewed from overhead. The antenna stands 50’ tall with 100’ top hat extending to a 140’ end-L. Antenna modeling with zero wire loss gets radiation resistance 0.84Ω and predicts these values:
Geometry Impedance dBi dBi dB zenith Front/back ratio
Ohms 20mS/m Perf.Gnd @ 10° elev.
“H” 0.84 –j 512 3.89 4.60 -10 0.8dB.
How do we find TRP to obtain a hypothetical 5 watt legal limit EIRP? (FCC action to allocate 630m to US amateurs with that limit remains pending. Get a Part 5 license to transmit now.)
5 watts is 37 dBm relative to 1 milliwatt, and 7 dBw relative to 1 watt. Assume 20 mS/m ground conductivity to model the antenna gain dBi. Or preferably model your antenna gain from your actual measured ground conductivity. Subtract the antenna gain dBi (relative to isotropic) from 7dBw.
TRP(dBw) = 7dBw – 3.89dBi = 3.11dBw
The maximum TRP to run is 3.11dBw. In watts,
TRPmax = 103.11dBw/10 = 2.04 watts.
This calculation is more aggressive than the usual short vertical calculation EIRP = 3 x TRP, where the conservative factor 3 corresponds to 4.77dBi. For antenna “H” the software would predict antenna gain 4.60dBi assuming perfectly conductive ground.
Next, get RF antenna current Imax = sqrt(TRPmax/ Rradiation). This RF current means antenna base current as measured at the output side of the ATU. For antenna “H” :
Imax = sqrt(2.04 watts / 0.84Ω) = 1.56A rms.
You can also do all the above calculations in reverse. For instance, Part 5 stations can approximately estimate EIRP this way: Start with the assumed or measured RF antenna base current I. Model the antenna to get the antenna radiation resistance and gain dBi. Then do the calculations in reverse. They boil down to:
EIRP(dBm) = 30 + 10log10(I2 Rradiation) + Gain(dBi).
This approach, of course, does not substitute for EIRP determination according to a more official method such as actual field strength measurement-based EIRP.
Antenna efficiency is the ratio of power radiated to power consumed by the whole antenna system including ground. That ratio is the same as radiation resistance divided by antenna system resistance including ground system resistance. We can discuss ways of estimating ground system resistance in a later blog post. For now let’s just assume 42Ω is the whole antenna system resistance including the ground system. For antenna H, in that case:
EfficiencyH = Rradiation / RSYSTEM = 0.84Ω/42Ω = 0.02 = 2%.
Next in our calculation hit parade comes TPO, which means transmitter power output. To estimate TPO:
TPOmax = TRPmax RSYSTEM / Rradiation = 2.04 watts x 42Ω/0.84Ω = 102 watts.
Remember that TPO is RF forward power minus the reflected power from the ATU input. If your SWR departs from 1.0 : 1, then the transmitter RF output power will need to be more than the TPO just calculated. And, of course, transmitter input power will likely need to be considerably higher than the transmitter’s RF output power.”
Additions, corrections, clarifications, etc? Send me a message on the Contact page or directly to KB5NJD <at> gmail dot (com)!