Last night started off slow and there were questions about whether the band was going to live up to our already unrealistic expectations of being strong on the first day of Spring. The band didn’t disappoint, yielding lots of WSPR reports and lots of activity with low to moderate noise levels. I often forget that as the days get longer, the band will open later and probably have shorter openings. Its just reality and physics. The good news is that when we have a large number of stations receiving and transmitting, its often easy to overlook the band conditions that are not yielding DX reports. I think guys just want to know that their signals are being enjoyed and utilized by someone. I’m extremely happy to see the amount of activity that we have recently had right on the precipice of what should be the release of rule for utilization of 630-meters under part-97.
There was a slight ping to the geomagnetic field during the afternoon in North America but Bz was only slightly south-pointing and the solar wind continues at moderate levels, above 430 km/s.
Neil, W0YSE/7 / WG2XSV, sent this waterfall screen capture of the “gang of 8” received at his station in the late evening. I note that when I came to check on my station at 0800z, the waterfall was full of signals just as Neil observed and it was clear that the band was wide open.
Neil also noted good conditions while running QRP ERP levels while he rebuilds his QRO amplifier:
Neil also had strong reports for such low power in Hawaii:
Doug, K4LY / WH2XZO, notes the the variations that occur, even for close stations. I agree with this variability as I often have a very different experience from stations that are nearby. Its similar to what is seen with 160-meter spotlight propagation.
John, WA3ETD / WG2XKA, experienced a typical session from his station in Vermont.
Ken, K5DNL / WG2XXM, reports that he decoded thirteen stations and was decoded by 43 unique stations. Ken also noted that he heard WH2XFI, operating at .1-watt ERP, thirteen times, with the best report at -17 dB S/N.
Ron, NI7J / WH2XND, reports that he decoded by thirteen stations in spite of local noise and was decoded by 43 unique stations while transmitting at 18.21-watts ERP.
Mark, WA9ETW, reports that he was receiving briefly during the session, with nine stations reported in his 45-minute operating window.
Its been reported on the RSGB-LF reflector that the IARU is planning for band plan discussions at its Region I meeting. While this might sound like a Region I problem, it has implications that might impact us here in North America in the future. I tend to believe that a hand-off attitude should be taken but I can also see the validity of protection for certain aspects of operating activities on the band. My biggest concern, which was echoed by many in reflector comments, is that people making these decisions in many cases have no idea what is going on at 472 and have probably never operated there. They refer to operators as “users” rather than knowledgeable operators about what works and what does not. Before making blanket recommendations, the people who actually use the spectrum should be asked for input. Follow this issue closely because it could result in mode realignment which could cause a disruption in operating until the dust clears. As Stefan, DK7FC, noted, the IARU should be focusing on increasing the maximum EIRP limit.
The MF QSO Party in Europe appears to have gone well with a significant number of active stations. Numerous anecdotal reports have been submitted so far. Markus, DF6NM, reported QSO’s with YO2IS, IZ7SLZ, SP9DNO, DL4YHF, G4GIR, DL6TY and DG3LV. I hope to see a summary of other’s activity shortly that can be detailed here and it would be my hope that activity nights like this can occur at least every quarter, even during the noisy summer months.
WSPR activity was once again very high, with 89 MF WSPR stations observed on the WSPRnet activity page at 0330z. AD5T was observed receiving during this session and may be a newer receive station, along with recent efforts in the south east from W5VE. The WSPR map was severely polluted during the daytime session due to a band selection problem that shows significant midday trans-Atlantic reports. The 24-hour maps will thus be less useful than they might normally be.
Regional and continental WSPR breakdowns follow:
There were no reports from the trans-Atlantic or trans-African path, however ZS1JEN was present during the session. UA0SNV was also present during the session but no reports were found in the WSPRnet database.
Eden, ZF1EJ, reports thirteen unique decodes from the Cayman Islands, including a few reports from WH2XCR.
Laurence, KL7L / WE2XPQ, had no reports for this session but weather in Alaska is very poor at the moment and this could be an indication that the power or Internet are currently down.
In Hawaii, Merv, K9FD/KH6 / WH2XCR, experienced reports from across the mainland US once again, including the easternmost portions of the US as well as both stations at ZF1EJ. He reported VK3ELV but no other reports on the Asian or Australian path were observed.
In Australia, Phil, VK3ELV, received reports from WH2XCR and JH3XCU:
Jim, W5EST, provides the next in a series of discussions on RF current entitled, “ANTENNA RF CURRENT READINGS, PART 3”:
“John WG2XKA e-mailed some much-appreciated experienced comments to this blog on the antenna RF ammeter topic. I’ve adapted them into dialog format for us all.
John XKA: One’s presence anywhere near a high-Q vertical system being tuned affects the scenario based upon your presence loading the antenna nearby.
Jim W5EST: What solution do you suggest?
John XKA: If I have to do a retune requiring tap change, variometer reposition, etc. I run an auxiliary 100′ run of coax from the tuning box (feedpoint, ATU) to the antenna analyzer so my human body capacitance does not affect the antenna. This saves multiple trips to/from my underground shack.
Jim W5EST: How do you read the RF ammeter without affecting the antenna by your physical presence? John XKA: I used an ampmeter when I first built the existing system. I placed an inexpensive cube ‘spy camera’ in the tuning box, so camera runs 2.4 GHz on a 9V battery. The receiver and 4″ TFT monitor allowed me to see it remotely. The two photos show the ammeter remote reading gear including Chinese vendor 2.4 GHz ‘spy’ camera and RX with homebrew gain bowtie antenna, and TFT monitor.
Jim W5EST: Clever, inexpensive solution! How did you come to think of it?
John XKA: I continue a long-time serious interest in R/C models of all types and have quite a collection of those Chinese camera rigs, both on 2.4GHz and 1296 MHz!
NOTES by Jim: Regarding antennas see this blog January 15-16 for a Q=150 circuit example and Feb. 9-11 on SWR and frequency adjustments. Picture an RLC circuit resonated for 630m. Ballpark numbers: 20 ohms antenna & ground system resistance, L = 1mH, C = 110pF, 3 RF amperes, Q=150, 13KV antenna voltage.
Estimate human body capacitance Cb equivalent to parallel-plate capacitor with A=0.025 square-meter area A and plate spacing d=0.20 meter (8”). You get 1.1 pF body capacitance.
Cb = εA/d = ~1.1pF = 8.86pF/m x 0.025 m2 /0.20m.
How much would 1.1 pF body capacitance affect the high-Q antenna resonant frequency given by 1/[2π sqrt(LC)] ? Answer: That much capacitance in parallel with the 110pF system capacitance lowers the resonant frequency by 0.5% of 475KHz or 2.4 KHz down to 472-473KHz. Any SWR measurement would also be way off–see illustration for Feb. 10, this blog.
Don’t try putting yourself near a fully energized TX antenna! That 13KV of 630m RF might or might not jump across the gap between the antenna base and you—don’t risk it!
Now, suppose you were foolhardy anyhow, and the RF didn’t spark over to you. How much capacitive current could pass into your body by diversion from the TX antenna? Answer: About 1% (=1.1pF/110pF) of the antenna current 3 RF amperes. That’s 30 RF milliamperes of diverted RF current. A word to the wise is sufficient: That’s a lot!
What would happen if you are in the shack and have a metal HF beam tower grounded and standing 20m tall and, say 10 meters (~33 feet) distant from the 630m TX top-hatted vertical? Rough answer: It would certainly add some capacitance. Because the tower is pre-existing, you would have used a bit less inductance to originally resonate the 630m antenna, so the Q would be somewhat less. A very rough estimate of the capacitance would be
Ctower = εA/d ~ ~0.18 pF = 8.86pF/m x 20 x 0.01 m2 /10m.
About 6 RF milliamperes would flow into the tower to ground due to the 630m coupling to the tower from the 630m TX vertical.
The tower would account for about 480Hz of capacitive reduction of the resonant frequency of the TX vertical relative to same real estate without the tower. That’s no problem because you resonate your 630m TX antenna with the tower already in place. If you take the tower down, or put in a tower where none existed before, then the 630m system may need retuning. Your numerical results can vary considerably from the very rough estimation here, especially for other antenna/tower dimensions and separations than those given.
Tell us your tips and ideas on the body capacitance and RF ammeter topics!”
Additions, corrections, clarifications, etc? Send me a message on the Contact page or directly to KB5NJD <at> gmail dot (com)!