Late evening band openings continue to be the highlight of recent sessions, some of which have been transcontinental in nature and at higher latitudes in spite of recent elevated geomagnetic conditions. Solar wind velocities currently exceed 500 km/s with Bz values pointing slightly to the North. Recent DST peaks are consistent with periods proceeding storm conditions, which have been forecast for a few days now. Time will tell if those conditions materialize.
It was nice to be able to keep the station on the air all night but storms did disrupt my morning CW sked as lightning was a bit too close to safely remain on the air.
Phil, VE3CIQ, reported improved conditions in Ontario and offers these comments:
John, WA3ETD / WG2XKA, reports similar improved band conditions in Vermont:
On the other side of the continent, Neil, W0YSE/7 / WG2XSV, reports that conditions in the Pacific Northwest were not as optimistic:
John, W1TAG / WE2XGR/3, reports, “Not a bad night, 12 stations reporting copy of the 20w (TX out) XGR/3 sig from ME. Best DX 1545km.”
Doug, K4LY / WH2XZO, is still working on his antenna maintenance project and reports that he will have to make another trip up the tower to untangle a couple of top load ropes and won’t be QRV before the weekend. He also reports that following a 6-meter QSO with ZF1EJ, its possible that Eden may be ready to transmit on 630-meters in just a few weeks.
Regional and continental WSPR breakdowns follow:
There were no reports from the trans-Atlantic or trans-African paths during this session.
Eden, ZF1EJ, decoded my station during this session.
Laurence, KL7L / WE2XPQ, returned to transmitting, making it to the Pacific Northwest and southwestern Canada during this session in addition to reports from WH2XCR.
Merv, K9FD/KH6 / WH2XCR, continues to see two-way reports with VK4YB in spite of significant noise from storms over New Zealand. Merv was not heard here overnight once again but was decoded by stations along western North America in addition to WE2XPQ in Alaska.
Jim, W5EST, presents this discussion entitled, “WHAT CURRENT DO I USE? WHAT IS MY AMMETER SAYING?”:
“I hope these FAQs delve into a familiar subject, but with a little different slant!
Q1: RMS RF current going through an RMS meter is divided by .707 to get Peak amps. Double the amps of RMS RF current through the RMS meter to get Peak to Peak amps. What current should we use to estimate Total Radiated Power? …we have Average, RMS, Peak and Peak to Peak!
A1: It depends on the power formula you want to use…Like sports, working on the fundamentals is worth it!
Q2: Thermocouple amp meters read in RMS. If your RF ammeter measures ‘average’ current, you multiply the reading by ~1.11 to get RMS. Do you really need to divide by .707 to get the peak current for antenna calculating? How should one interpret Fritz’ formula (5) “Given Rr and the peak current I delivered to the antenna, the Total Radiated Power is Pt = I2Rr / 2 ” (Link, see endnote.*)
A2: To get peak current (zero-to-peak of the sine wave) from RMS, yes, divide by .707. But you don’t necessarily have to start with peak current to apply some Total Radiated Power formula that will work. Actually, several formulas all work. Choose whichever one you like!
Pt = Irms2 Rr
Pt = Ipeak2 Rr / 2
Pt = 1.233 Iavg2Rr
Pt = Ip-p2 Rr / 8
Q3: But isn’t the average of a sine wave equal to zero?
A3: RF ammeters have a construction like D’Arsonval in which the needle moves because its coil-current is inside a magnet and responds to average current. The reading would indeed be zero without some circuit to deliver the current magnitude (departure from zero, sign ignored) for the meter to average. Alternatively, a thermocouple-based meter uses current to heat up a bimetal strip, where the strip responds to power. Power relates to current-squared, not current directly.
But, meters also have their calibration, which doesn’t depend entirely on the construction type. A meter face can be marked a lot of different ways. That’s because formulas specific to each waveform shape, like sine wave, interconnect all those four types of current measures: For sine waves they’re .707 Ip-p/2 = .707 Ipeak = Irms = 1.11 Iavg. Any type of analog or digital ammeter can be calibrated, marked, programmed to read out any of those four current measures– Average, RMS, Peak and Peak to Peak.
Q4: An FCC article doesn’t refer to Peak or Peak to Peak in this link. What gives?**
A4: I think FCC just wants stations to comply with their applicable regulations and Part 5 stations’ license terms. Otherwise, stations might radiate too much power and risk interference. Above, I talked about Total Radiated Power. When the applicable power limit is stated as EIRP, don’t forget to multiply Total Radiated Power by the appropriate factor or add the appropriate dB to estimate whether your planned transmit power and antenna will be compliant. At the end of the day, official methods of measuring compliance will govern.
Regarding ammeters, have some fun and check your understanding of this blog post. Try figuring out which type of current the homebrew RF ammeter on another web site*** is measuring!
Additions, corrections, clarifications, etc? Send me a message on the Contact page or directly to KB5NJD <at> gmail dot (com)!