630-meters was quite good overnight, certainly better for mid and lower latitudes than the previous session which was full of propagation oddities. Geomagnetic storm levels were reported overnight elevating K-indices and solar wind velocities, which were already above 400 km/s. The Bz is currently pointing the the North but pushed to the South during the greatest periods of impact to the Kp. DST values observed the typical “peak before valley” at the onset of storm levels.
Neil, W0YSE/7 / WG2XSV had a laughable QRO report during the session and also note similarities to observations of Laurence, KL7L / WE2XPQ. Neil provided the following details and statistics:
Phil, VE3CIQ, also noted a good band with propagation beginning to stretch out again:
Ken, K5DNL / WG2XXM, has dried out, if only temporarily, and was able to operate during the session, decoding three WSPR stations and being decoded by 19 unique stations.
Wolf, DF2PY, reported at 1933z that he was QRV on 472.5 kHz CW. Wolf has maintained quite a bit of CW activity on the band as we move closer to summer. Please listen for him and give him a call.
The combined pair of keyed CW amps did well this morning but I found that the bug needed a bit of adjustment and contact cleaning. Because I am keying a relay whose contacts present simultaneous contact closures for each of the amplifiers, there is a back-EMF generated when the relay coil opens. The spark on the contacts has resulted in residue deposits which resulted in erratic keying during today’s sked. After completing the sked I spent an hours making adjustments, cleaning contacts and testing a diode across the bug terminals to suppress the back-EMF. It seems I was successful and only further on-air testing will determine whether further work needs to be done. Keying the relay changed the character of the bug keying that I had grown accustom to so there will be another readjustment period to the new parameters.
Regional and continental WSPR breakdowns follow:
There were no reports from the Caribbean, trans-Atlantic or trans-African paths. UA0SNV was present but no reports were submitted during this session.
Laurence, KL7L / WE2XPQ, was QRT during this session.
Merv, K9FD/KH6 / WH2XCR, had what could probably be considered a better session if for no other reason than he heard WG2XXM in Oklahoma. This path has eluded my signals (and Merv’s signals) for the past few weeks just 200-miles to the South so perhaps we have turned a corner and improvements are on the horizon. The two-way path with VK4YB was also open bu no reports from VK2XGJ.
Jim, W5EST, is presenting and commenting on another technique that I have utilized for a few years with great success in this discussion entitled, “HOW AN RF POWER COMBINER WORKS”:
“I’m repeating John’s WG2XIQ commentary* on the W1VD zero-degree combiner and add some of my notes [in brackets] too. Here, I’ve redrawn the combiner schematic without changing the circuit connections. As illustrated, it depicts each coax-wound toroid T1 or T2 like a transformer using a coax center conductor and its concentric shield as transformer windings in schematic.
The winding sense of 1:1 transformer T1 is shown by labeling “T1” by each winding in the places of the usual dots. Ditto for T2. Winding voltage unknowns v1, v2 turn out to be near-zero when the bridge or lazy-H circuit is driven by both transmitters TX1 and TX2. T3 is an impedance-matching transformer matching its 25Ω input to 50Ω output.
“Combining is the act of taking two or more signals that are in all ways equal and adding them together in-phase [AT T3 INPUT]. Variations in phase relationship or amplitude result [IN NONZERO DIFFERENCE (I1-I2) CURRENT] in a portion of the power being rejected, typically to a resistive load [RLOAD] and wasted as heat. A well isolated two-port system [TX1, TX2] will still see a 50 ohm load resistance even when the second port [TX2] is inactive or no amplifier is present, however, half of the power from the operating port will be lost to the resistive load [RLOAD] as heat.
The process starts with an input signal that is typically from a single source but can come from multiple sources as long as they are phase locked….[D]ownconverter output passes through a small attenuator whose output is a T-splitter. The splitter is the connection point for equal lengths of coax to drive each amplifier. And I mean EQUAL LENGTHS. If you are duplicating this project and are unsure of your ability to build two, absolutely identical cables, buy the machine-built cables from a reputable seller. They will likely be identical. Each identical cable connects to an identical amplifier.”
“The outputs of each amp [TX1, TX2] feed each input port of the combiner [T1, T2] with IDENTICAL cables. The output [T3, 50 ohm side] of the combiner can be any length but should pass through a low pass filter [LPF] that is capable of handling the output power…[O]utputs of combiners are apparently pretty harmonic rich… W1VD zero-degree combiner…. port isolation is phenomenal and I know that my amplifiers are going to see 50 ohms even if one should fail.”
In this way the combiner delivers twice the power of each transmitter TX1 or TX2 alone. The combiner sees the antenna system as 25Ω at the input of its transformer T3, which impedance matches the two 50Ω transmitters TX1 or TX2 effectively put in parallel 50Ω/2 by the combiner.
Suppose transmitter TX2 goes off-line (open T2 input at lower left). Then the other winding of T2 at upper right presents a very high inductive reactance amounting to a near-open circuit there. Now voltages v1 across the windings of T1 are no longer zero, but they do cancel each other. That leaves 25Ω RLOAD in series with the 25Ω offered by the input of transformer T3.
This way, transmitter TX1 remains matched to 50Ω and delivers half its TX1 power to the antenna and ground system even if transmitter TX2 goes off-line. Compared to power from both transmitters TX1 and TX2 active, the radiated signal level when TX2 goes off-line falls by 6dB, or a factor of 4. But this 630m system is still on the air!
Depending on particular TX1 and TX2 circuitry and failure scenarios and possible shorting of cable connections, suppose TX2 fails to a low impedance instead of an open circuit (or some essentially-equivalent high impedance). In that case, 25Ω RLOAD power dissipation can go into action. The remaining transmitter TX1 would likely see a departure from 50Ω match that’s somewhat less-serious at its TX1 output than for hypothetically failed TX2.
Lastly, consider a scenario in which the antenna system becomes disconnected or significantly altered due to wind gusts, or Murphy’s Law attacks the system or circuitry some other way. The impedance at the input of transformer T3 changes significantly and the change is symmetrically presented to the outputs of transmitters TX1 and TX2. To handle that scenario, it may be desirable to have an SWR cutout or other PA protective circuit to shut down each transmitter. 25Ω RLOAD power dissipation remains near-zero under that scenario.
Comments? Other circuits? Your experiences? Let us know!”
Additions, corrections, clarifications, etc? Send me a message on the Contact page or directly to KB5NJD gmail dot (com)!