This night was another slow starter but it did not disappoint. WG2XXM found the right duct to crawl into, resulting in his WSPR signal being decoded by three German stations. In the western US WH2XGP, WH2XXP, and WH2XND were reported by VK4YB. WG2XKA scaled the high latitude northern path to be reported by KL7L/VE6. Both stations in the Cayman Islands reported WH2XCR in Hawaii. All this happened with a noisy storm system that was crawling across the Midwest of the US. The band was open in spite of the fact that receiving might have been tough in and around these storms.
The geomagnetic field experienced a few periods of elevated activity but the geoeffective coronal hole was never a major source of negativity for the session.
John, WA3ETD / WG2XKA, experienced a nice surprise on the high latitude path to VE6 and provides these comments and his session WSPR map:
Ken, K5DNL / WG2XXM, decoded eleven stations and was decoded by 45 unique stations, including three Germans.
Phil, VE3CIQ, notes a slow start and QRN complicating the session but he decoded ten stations, the furthest being VE7BDQ. Phil was decoded by seventeen stations, the furthest being ZF1EJ.
Larry, W7IUV / WH2XGP, decoded nine stations and was decoded by 37, including VK4YB.
Ward, K7PO / WH2XXP, and Ron, NI7J / WH2XND, were also reported by Roger, VK4YB, during this session:
Roelof, PA0RDT, reports that Joe, VO1NA, was received at his station on 477.7 kHz:
Regional and continental WSPR breakdowns follow:
There were no reported from the trans-African path, however ZS1JEN was present. UA0SNV was also present during this session but no reports were found in the WSPRnet database.
WG2XXM received the sole trans-Atlantic reports during this session:
EA8/DL9XJ, reported three WSPR stations in continental Europe:
Very good propagation in the Cayman Islands resulted in WH2XCR reports for both Eden, ZF1EJ, and Roger, ZF1RC. Eden’s second stations, ZF1EJ/1, also reported Merv. If I am not mistaken, this station is using the small loop.
Laurence, KL7L / WE2XPQ, continues his remote operation from VE6 where propagation was very good, with reports of WG2XKA, WH2XCR and all points in between. He also provides some details of his antenna set up:
Laurence’s station in Alaska received the usual stations in the western US and Hawaii, in addition to WG2XXM in Oklahoma:
In Hawaii, Merv, K9FD/KH6 / WH2XCR, continues his pursuit of VK0 on 160-meters but was able to provide a number of reports for stations across North America and Australia.
In Australia, Phil, VK3ELV, and Roger, VK4YB, continue to receive reports from WH2XCR. Roger had the distinction of two-way reports with Merv. Phil received late JA reports from the previous session that are included below:
Jim, W5EST, provided the following discussion entitled, “RF CURRENTS IN 630M TRANSMITTING SYSTEMS (LOW LOSS ATU)”:
“Joe mentioned lossy ATU coils in last Friday’s dialog, this blog 3/25/16, and I’ll discuss them in a future post too. Today, let’s talk about 630m/2200m ATUs when they achieve 1:1 SWR and provided their losses are small compared to the grounding system losses plus all other ohmic losses in the whole antenna system. At 1:1 SWR, forward power is the entire TPO (transmitter power output), assuming the transmission line to the ATU also has negligible loss compared to the rest of the system. “ATU” means everything between the coax and the base of the antenna whether or not some loading inductance is mounted external to the ATU enclosure.
Any low-loss ATU– no matter how one or more capacitors or coils or variometers or RF transformers or even lengths of coax might be connected in any circuit arrangement inside– transfers to its output essentially all the RF forward power arriving at its input when SWR is 1:1. That general statement must be true when the ATU losses are negligible because the RF forward power has nowhere else to go except to the ATU output. What indeed does depend on the ATU circuit arrangement inside is the output current and voltage.
Moreover, any low-loss ATU that achieves 1:1 SWR at its input will inherently match its output to the antenna system regardless of the construction of the antenna system and construction of the low-loss ATU. Match to the antenna system means that the low-loss ATU cancels the antenna system reactance X and transforms the 50Ω coax characteristic resistance to precisely equal the antenna system resistance RANT. Seems like magic! But it’s simply a consequence of the TX power (TPO) passing undiminished through a low-loss ATU.
In 630m/2200m Part 5 and ham stations, antenna system ohmic loss (including ground loss) accounts for almost all the antenna system resistance RANT. Meanwhile, the “good” radiation resistance (the antenna’s ability to convert some of the TPO into total radiated power TRP) is quite small by comparison to the lossy ohms of earth ground resistance and conductor skin affect in antenna, cap hat and radials.
What does all this mean for current, voltage and impedance transformations by the ATU at 1:1 SWR ?
First, the ATU matches 50Ω coax input to the total ohmic system resistance Rsystem.
Second, “low loss ATU” means power out equals power in: Iout2 Rsystem = Iin2 50Ω. So the output current of the ATU is related to the input current to the ATU by
Iout/Iin = sqrt (50Ω / Rsystem).
Generally at 630/2200m, Rsystem is between 5 and 40 ohms and more often between 15 and 30 ohms. If TPO is 100 watts, RF coax current into the ATU is:
Iin = sqrt(TPO/50Ω) = sqrt (100 watts/50Ω) = 1.4A rms.
Suppose system resistance were 25Ω. Then the antenna base current will be:
Iout= Iin sqrt (50Ω / Rsystem) = 1.4A sqrt (50Ω/25Ω) = 2.0A rms.
Third, the voltage output of the ATU is the RF voltage developed by the current flowing through the system resistance Rsystem and reactance jX. Suppose, with antenna base disconnected from the ATU, an antenna analyzer accurately measures the antenna base impedance Rsystem+jX to be 25 –j3000 ohms (capacitive).
Then at 1:1 SWR the ATU output voltage Vout at input of antenna base is
Vout = Iout (Rsystem + j Xsystem) = 2.0A rms x (25 – j3000)Ω = (50 –j6000)V, or about 6KV rms.
That means about 8.5 KV peak RF voltage since peak voltage is 1.41 x rms voltage.
Fourth, the ATU’s lossless or low-loss power transfer means that VsysΩ Iout =Vin Iin. Consequently, the voltage VsysΩ developed in the antenna system resistance has to be:
VsysΩ / Vin = Iin / Iout
The ATU input voltage is Vin = sqrt(TPO x 50Ω) = sqrt (100w x 50Ω) = 70.7V rms in the coax or 100V peak RF voltage on the coax input to ATU. (And the loss in the coax should generally be even lower at MF/LF than at HF or VHF.)
The voltage developed in the antenna system resistance alone (compared to the actual kilovolts across the –j3000Ω antenna capacitive reactance) then is:
Vin Iin / Iout = 70.7Vrms 1.4A rms /2A rms = 50V rms.
Fifth: You might wonder how the ATU can step up current like a transformer but without a transformer! Suppose the circuit in the ATU is an L-network, for instance. That’s the magic of lossless power transfer networks generally! Indeed it’s true of transmission lines too!
Lossy ATUs can be the topic of another day. In the meantime, if you have words of wisdom from your experience, let us know so we can blog them!”
Additions, corrections, clarifications, etc? Send me a message on the Contact page or directly to KB5NJD <at> gmail dot (com)!