It was noisier than the previous session but the band was very active as WSPR dominated the session with 82 MF WSPR stations observed at 0330z. Geomagnetic conditions were very calm, however, Solarham reports that we should already be observing storm levels. Solar wind is currently elevated above 400 km/s but conditions remain quiet for the moment. The DST often increases before storming levels begin to present and we have seen that behavior through this session.
Dave, G4FRE, reports his first trans-Atlantic report of 2016 at his station, receiving WG2XJM during the session. He reports that he was using an Elecraft K3S and PA0RDT E-probe. Dave provided the following picture of his path to North America, which happens to have a hill “in the way”:
Neil, W0YSE/7 / WH2XGP, reports good band conditions, decoding eight WSPR stations and being decoded by twelve, as he continues to operate at 200 mW ERP.
Mike, WA3TTS, provided the following report and statistics from his station near Pittsburgh:
Ken, K5DNL / WG2XXM, reports that he decoded eight unique WSPR stations and was decoded by forty WSPR stations including VK4YB.
Larry, W7IUV / WH2XGP, reports that he decoded ten unique WSPR stations and was decoded by 38 WSPR stations including VK4YB.
Phil, VE3CIQ, reports that he decoded six unique WSPR stations and was decoded by 16 WSPR stations including two-way reports with WH2XGP.
Steve, VE7SL, reports that he decoded twelve WSPR stations including WI2XFI and “the rare VE3CIQ” in the East.
Regional and continental WSPR breakdowns follow:
There were no reports from the trans-African path. UA0SNV was present from Asiatic Russia but no reports were found for Vasily in the WSPRnet database.
Eric, NO3M / WG2XJM, experienced a good session of trans-Atlantic reports from a number of stations and Stefan, DK7FC was reported by WD2XSH/17.
In the Caribbean, Roger, ZF1RC, reported four North American stations during the session. Eden, ZF1EJ, reported three stations on 630-meters but due to a data problem, the map is not included.
In Alaska, Laurence, KL7L / WE2XPQ, was reported along the West coast of North America as well as Hawaii. KL7L was designated as receive-only and reported stations in the Pacific Northwest and Hawaii.
In Hawaii, Merv, K9FD/KH6 / WH2XCR, continues to experience distant two-way report with VK4YB and WG2XJM. The Japanese path continues to be cut off.
In Australia, Phil, VK3ELV, and Roger, VK4YB, received reports from WH2XCR. Phil, received additional reports from three JA stations, with 7L1RLL_4 and TNUKJPM reports coming from late in the previous session.
Jim, W5EST, provided this technical discussion entitled, “MF/LF ANTENNA DEGREE-AMPERES”:
“Have you ever wondered what antenna degree-amperes are for? Here’s my take.
RF current along the length of a vertical generates the oscillating magnetic field to launch your RF signal. Degree-amperes numerically express a quantity that when squared (degree-amps)2 relates to total radiated power TRP. The idea is to multiply an average value of RF current (as if it were uniform over the whole vertical antenna height) times the electrical length in degrees of the vertical height of the antenna system. More height and more average current jointly make more TRP. A quarter-wave vertical would stand roughly 90° tall. Degree-amps capsulize an area-under-the-curve of nonuniform current distribution along vertical height.
But on 630m, verticals are electrically short. A vertical 20m tall occupies 11.4° on the 630m band. Most Part 5 and non-USA ham 630m verticals are electrically 5° to 10° tall. On 2200m the same verticals are 1.5° to 3° tall. If you run 1.5A RF averaged over height, that’s 7.5-15 degree-amps on 630m and 2.25-4.5 degree-amps on 2200m.
Using electrical degrees instead of multiplying by the length itself recognizes that the same vertical height of antenna, when driven with the same RF current, radiates less TRP at lower frequencies, longer wavelengths. If you read somewhere about ampere-radians, just remember that 1 radian = 57.3° and it’s the same thing in concept as degree-amperes.
Field strength as measured by field strength meters is directly proportional to degree-amperes. The next web site says 1 degree-amp gives 1.04 mV/meter at 1 kilometer. Nice! http://www.vias.org/radioanteng/radio_antenna_engineering_01_06_01.html , citing E. Laport.
I hope to talk more about RF field strength in a blogpost some future day. In the meantime, let’s get better acquainted with degree-amperes today and critique top hats tomorrow.
A vertical without a top hat has no current at its tip, meaning most of the upper part of a hatless short vertical is inefficiently used. Average RF current along the hatless vertical’s height becomes half what the RF ammeter shows. If there were current at the hatless tip, the antenna would be undesirably sparking and going nonlinear!
Talking about RF base current and estimated radiation resistance Rradiation just gives you an different way of picturing the same thing as degree-amperes. You may see a radiation resistance formula that’s proportional to the square of the fraction that the antenna vertical height bears to the wavelength. Rradiation = a2 (h/λ)2. The fudge factor a2 depends on the amount of top hat and gets you to ohms. On the above web site you you see a log-log graph to straighten out the squared quantity (h/λ)2 . It includes various graphical straight lines for different top hats–different values of the constant a.
The antenna design jargon of degree-amps and radiation resistance Rradiation flow from one same idea—power equals I2R. Total radiated power is TRP:
TRP = Ibase2 Rradiation.
The degree-amps approach recognizes that the fudge vector a2 depends on the amount of top hat because that affects the RF current distribution:
TRP = Ibase2 Rradiation = Ibase2 a2 (h/λ)2.
When you massage the equation you see that constant a takes you from antenna base RF current to the average current along the whole vertical height of the antenna system. What’s inside the brackets is proportional to degree-amperes.
TRP = [a Ibase h/λ]2
TRP is proportional to the square of field strength at 1 kilometer, and field strength itself is proportional to degree-amperes. One could get really technical about the math, but this is enough for now. Remember that EIRP is triple the TRP of a short vertical!
For more background on the subject of degree-amps see your favorite antenna textbook, or see pp. 16-7 and 16-8 in this additional web site: http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0ahUKEwjks977u-vLAhXIMyYKHcy1C5sQFggiMAE&url=http%3A%2F%2Fwww.qrz.ru%2Fschemes%2Fcontribute%2Farrl%2Fchap16.pdf&usg=AFQjCNEBblgaRaN6sca4IbD9xc9IqB8Mcw “
Additions, corrections, clarifications, etc? Send me a message on the Contact page or directly to KB5NJD <at> gmail dot (com)!