This week’s main weather event, at least here in Texas, arrived overnight. This event impacted a much wider area than just Texas, however, and the lightning map across North America was extremely active. Eventually weather will calm down and then we can get back to worrying about propagation and why it isn’t behaving properly.
Geomagnetic conditions were quiet but elevated compared to the previous session. The Bz has been elevated to moderate levels exceeding 10 nT and solar wind velocities are at moderate levels, above 400 km/s.
Neil, W0YSE/7 / WG2XSV, was reported numerous times in Alaska during the session:
Regional and continental WSPR breakdowns follow:
There were no reports from the trans-Atlantic or trans-African paths during this session. UA0SNV was present but no reports have been submitted.
In the Caribbean, Eden, ZF1EJ, continues to report WH2XZO in South Carolina:
Laurence, KL7L / WE2XPQ, reports that he will be operating in a receive-only capacity for a few days. Laurence notes that in the previous session his software defaulted to JT65 after power returned which explains the limited activity from his station. He also reports elevated VLF conditions with significant chorus being heard under band conditions that are somewhat better compared to the past when a neighbor’s noise source impacted his activity. During this session, Laurence reported WG2XSV and WH2XGP:
Merv, K9FD/KH6 / WH2XCR, was QRT during this session.
Jim, W5EST, presents “PART 5: VARIABLE PHASING: TX VERTICAL AND SHORTER RX VERTICAL”:
“An accompanying Phasing/Cancellation illustration here shows a phase diagram for noise cancellation. The diagram is based on yesterday’s blogged big-dog/little-dog vertical antenna duo separated by 50 feet (dsep ~15m). A noise canceler unit phases the antennas at various out-of- phase angles to obtain different antenna patterns shown in the Phased Antenna Patterns illustration. The canceler circuits are configured and adjusted either to attenuate the reception from the large TX antenna system or to amplify the reception from the small RX vertical, or do some of both.
Isn’t this a phased array and not a noise canceling system? Short answer is “Both!” Often “phased array” makes one think of two or even many identical, same size antennas that are enhanced in directivity by phasing. Noise canceling systems often use just two antennas, which not infrequently do differ in size or type. It’s fine to call this antenna duo by whatever name you like.
In the Phased Antenna Patterns illustration, elevation patterns morph into each another, as do the azimuth patterns, when you manually adjust a noise canceller unit. The antenna duo is unidirectional in opposite directions corresponding to phasing 170° vs. 190° in my specified model Sources. The antenna is bidirectional at 180° phasing, and the bidirectional pattern peak is about 6dB down from the unidirectional pattern peaks. To get unidirectionality, the canceler’s phase departure from180° is proportional to the distance between antennas. In this example, each main lobe always lies along the axis line between the antenna bases without beam steering through heading angles away from the axis.
With bidirectional 180° phasing, the solid angle A at 3dB down from its pattern peak is A ~= [34.9° x 2 x 91.6° cos((34.9°+2°)/2)]/57.32 = 1.85 steradians.
Beamwidth Figure of Merit at 180° phasing is F = 2π/1.85~= 3.4.
This performance is not bad compared to the F=4.2 value unidirectional phasing of the system yields. It’s quite good performance compared to F=1.3 for a single vertical.
You can estimate possible SNR enhancement by reduction of band noise power compared to a vertical. Think of such band noise as if uniformly distributed in azimuth and elevation. Take dB = 10log10(F/1.3).
That dB formula suggests a nominal band noise reduction 4dB to 5dB for various phase settings of the big/little vertical duo. Actual performance may be better or worse depending on the azimuth and elevation distribution of real 630m band noise.
The Phase/Cancellation diagram helps make sense of the pattern diagrams that the antenna modeling program delivers. When phasing is set near a special value around either 170° or 190°, then a signal arriving along the axis from one direction will be canceled while a signal arriving from the opposite direction will be only partially reduced in amplitude. The axial lobe sizes depend on the phasing. By thinking in terms of both the phase diagram and a pattern diagram, you start getting an intuition for the noise canceling performance and capabilities of a given antenna system.
Phasing the two antennas at 180° provides two lobes with azimuth pattern nulls between them. The out-of-phase antennas thus totally cancel each other laterally either side of the axis line between the verticals. That’s consistent with the bidirectional pattern shown in the middle of the second illustration.
The bidirectional pattern peaks are 6dB down from the unidirectional pattern peak because the voltages of an arriving RF signal from forward of the two antennas have a phase difference. (Compare the dBi gain values at the right-side text of the pattern diagrams to see the 6dB difference.) That phase difference is small compared to what those voltages take on when the phaser effectively adds more phase difference by departing from 180° to the unidirectional 170° and 190° phased conditions. More phase difference means about double the combiner voltage output. Since dB is a power ratio, the 2x voltage is squared and leads to 6dB more power for the unidirectional patterns.
The RX vertical may detune the TX vertical somewhat. Transmit/Receive switching may need to take that into account so that everything works properly on both transmit and receive. Let us know your transmit/receive arrangements!
Because of narrower forward beamwidth at 180° phasing, compared to 170° and 190° phasing, the 180° setting may provide some noise rejection advantage. Also, if it is desired to receive from both the front and the back of the system, the 180° phasing is preferable. The desirable canceller settings will depend on the geographic position of your QTH, the geographic positions of any prominent sources of band noise, and the heading of the axis line between the verticals relative to headings of stations you want to receive well.”
Additions, corrections, clarifications, etc? Send me a message on the Contact page or directly to KB5NJD gmail dot (com)!