This session turned out to be really very good on the trans-Atlantic path including first-time 630-meter WSPR trans-Atlantic reports at KC2QII in South Carolina. Domestic paths, particularly the high latitude transcontinental path, were not bad either, as reported by John, WA3ETD / WG2XKA, in Vermont:
The geomagnetic field remains relatively quiet although solar wind velocity continues above 500 km/s.
Roelof, PA0RDT, provided the following report of his CW reception of Joe, VO1NA, on 477.7 kHz:
I spent about an hour on 630-meter CW last night before QRTing for the session due to impending storms and was listening witth the FT-1000 Mark V using the HD-1420 receive converter. This was a very quiet and effective receive combination. The typical MF receiver is the FT-920 using the same converter but its my feeling that the Mark V is significantly quieter. Had received signals not been so strong, I would have assumed there was a problem given that the noise floor was so low. While I have been hesitant to transition to the Mark V full time as it is the anchor rig at the HF position in my station, I suspect it is the heir-apparent. The original plan was to transition to the Elecraft KX3 as the FT-920 life cycle comes to an end but with no receive-only antenna port on the KX3, I would have to implement outboard antenna switching and sequencing, something that the Mark V (and FT-920) already accomplish internally. Expect to hear the Mark V in full-time MF service at WG2XIQ shortly.
Mike, WA3TTS, had a number of nice catches through the session and provided the following detailed report:
Neil, W0YSE/7 / WG2XSV, found a lot of success at QRP ERP levels from Vancouver, Washington:
Ken, K5DNL / WG2XXM, reports that he decoded ten stations and was decoded by 42 unique stations.
Phil, VE3CIQ, reports that he decoded seven stations and was decoded by 17 unique stations, including two-way reports with VE7BDQ and WH2XGP.
Larry, W7IUV / WH2XGP, reports that he decoded eight stations and was decoded by 35 unique stations, including VK4YB.
WSPR activity dominated the session, with 87 MF WSPR stations observed at 0400z on the WSPRnet activity page. WB4SPB was a new reporting station during this session.
Regional and continental WSPR breakdowns follow:
There were no reports from the trans-African path. UA0SNV was present from Asiatic Russia but no WSPR reports were found in the WSPRnet database.
The trans-Atlantic path was active during the sessions, with reports on both sides of the Atlantic. DK7FC and PA0RDT provided a few comments about the opening on the RSGB-LF reflector, followed by the session trans-Atlantic details:
Eden, ZF1EJ, and Roger, ZF1RC, provided reports for stations in the US in spite of a few storms in Florida that were no doubt making listening difficult.
Laurence, KL7L / WE2XPQ, spent his last night in VE6 providing reports from this remote outpost:
Laurence’s station in Alaska, WE2XPQ, is either off-air or experiencing upload problems as there were no reports for this call sign in the previous 24-hours.
In Hawaii, Merv, K9FD/KH6 / WH2XCR, received reports from the eastern US, Japan, and Australia, which included two-way reports with VK4YB.
In Australia, Phil, VK3ELV, and Roger, VK4YB, receive reports from WH2XCR. Phil also received reports from two stations in Japan, a few of which were received late in the previous session.
Jim, W5EST, provided part 3 in a series entitled, “ESTIMATE SERIES OUTPUT LOSSES 630/2200M IN ATU WITH ANTENNA ANALYZER”:
“Summary: An antenna analyzer can isolate RLOSS by resonating a variable capacitance in series with the ATU loading coil alone. Subtract RLOSS from total RLOSS + RSYSTEM measured by an antenna analyzer across the combination of a loading coil via ATU output to the antenna system. See illustration.
Discussion: ATU power loss is proportional to RLOSS compared to all the outdoor resistances.
PATU/TPO = RLOSS/(RLOSS + RSystem) = (1.0 minus ATU efficiency).
If the ratio exceeds 5%, the ATU power loss probably is significant enough to alter calculations that presume a lossless ATU.
How can one measure these resistances? An antenna analyzer may not measure antenna system resistance and reactance accurately if either of them depart quite far from 50Ω. http://www.zl2pd.com/digitalZmeter.html (Click on Appendix A for the theory of operation.) https://en.wikipedia.org/wiki/Antenna_analyzer (bridge)
A 630m antenna is likely to have a large capacitive reactance like -j1000 to -j4000 ohms. The loading coil likewise will have a large inductive reactance like +j1000 to +j4000 ohms–roughly equal in magnitude to the antenna system capacitive reactance.
Using an L-network ATU as one example, you can adapt the measurement technique here to measure loss resistance in your particular ATU’s circuit. See illustrations. It’s assumed the ATU was set up beforehand and adjusted to match the system as well as possible to a 50Ω coax line.
First of all, make sure the TX is turned off and will not be disturbed while you are outdoors or otherwise making these resistance measurements. Record any original tap connections and/or adjustment settings so that you can return the ATU its original state at the end of the measurement process.
Disconnect the TX coax from the ATU input. Connect an antenna analyzer to the ATU input in place of the TX coax. Use an analyzer unit that reads each of resistance and reactance at an MF/LF ATU working frequency such as 137.5 KHz or 475.7 KHz. Disconnect the L-network tuning capacitor from the coil, leaving the coil connected to the ATU input and leaving the antenna system connected to ATU output. The coil should cancel most of the antenna system capacitive reactance, enough for the analyzer to show a reasonably steady measurement of resistance. Do the measurement standing far enough away from the ATU to avoid body capacitance disturbing the result. Record the resistance value shown on the analyzer display: Measurement = RLOSS + RSystem. Suppose for example you get 27 ohms.
Likewise record the reactance magnitude XC displayed by the analyzer. Determine antenna system capacitance C= 1/(2πf XC). C ~= 330/XC pF for XC in Kohms at 630m from the analyzer. C ~= 1150/XC pF at 2200m. Antenna system capacitance may be on the order of roughly 100 pF.
Next, as shown lower in the illustration, connect the antenna analyzer to the ATU output after also disconnecting the antenna system from the ATU output. By “output” I mean the output that’s connected to the base of the antenna, even if that’s from an external section of loading coil. Leave the ATU input disconnected. See if the L-network capacitor can be adjusted to a low enough capacitance to cancel most of the inductive reactance in the ATU and give a reliable measurement of resistance RLOSS. If you need a lower capacitance than that, then interpose 100 to 200pF of noncritical good quality fixed capacitance in series, as illustrated, between the ATU variable capacitor and the L-network coil. Try again until you can satisfactorily measure RLOSS. Let’s say you get 1.5 ohms.
Why not just use a multimeter ohmmeter to measure RLOSS? Because loss resistance RLOSS at RF is likely to be considerably higher than at DC due to skin effect, for instance. Will the antenna analyzer be able to measure RLOSS if its value is just an ohm or two? Good question. At the outset it may be a bit tricky to find the sharp resonance point of the coil/capacitor circuit to nearly cancel j1000-j4000 ohms reactance so the analyzer can reasonably measure RLOSS.
You can put a carbon resistor (5Ω-10Ω noncritical) in series and analyzer-measure the resistance difference with and without the loading inductor, to obtain RLOSS. That way you measure more confidently and make the test circuit resonance less critical to find in the process.
Given success so far, the RLOSS value you find may indeed be quite low-ohm in value. But if it is, that’s good news. For our MF/LF experimental purposes, you just want to know that RLOSS is less than about 5% of the antenna system resistance. If so, then perhaps you don’t really need to care if a measured value less than one ohm is imprecise.
Finally, return the ATU to its original state by restoring the original internal connection of variable L-network capacitor to loading coil, adjusting the capacitor to its original setting, reconnecting ATU output to antenna base, and lastly reconnecting TX coax to ATU input. At low TX power make sure the SWR is still 1:1 or SWR minimum you had originally achieved. If not, slightly adjust the variable L-network capacitor to restore the minimum SWR.
Use your measurements to find out whether the ATU power loss is significant:
PATU/TPO = RLOSS/(RLOSS + RSystem) > 5%? In our example, PATU/TPO = 1.5Ω/27Ω = 5.6%.
Calculate the antenna system resistance RSystem by taking the difference of the resistance values you found.
RSystem = (RLOSS + RSystem) – RLOSS. Example values give RSystem = 27Ω – 1.5Ω = 25.5Ω.
An L-network transforms impedance (RLOSS + RSystem) to 50Ω and transforms the loss resistance RLOSS proportionally. Looking into the ATU input, the loss resistance becomes the ATU resistance RATU discussed yesterday. Here, RATU = 50Ω xRLOSS/(RLOSS + RSystem). In the example, RATU = 50Ω x 1.5Ω/27Ω = 2.8Ω RF resistance at working frequency.
Notice that none of the measurement steps have used an RF ammeter. Beforehand, you can measure the TPO and also use scope match or an SWR bridge that works at MF/LF to determine whether you are matched to 50Ω or not. TPO is forward power at 1:1 SWR. At some other SWR, TPO is forward power minus reflected power for the measurement purposes.
Have you tried this ATU loss resistance measurement method? Let us know what measured values you obtained. Tell us what your practical experience taught you if you tried to reduce your ATU losses!”
Additions, corrections, clarifications, etc? Send me a message on the Contact page or directly to KB5NJD <at> gmail dot (com)!