Bob,

The attached plot shows some interesting aspects of the 74.54xx kHz links on Sunday night / Monday morning.

Aspects that caught my attention as grabber images arrived from Henny, Hartmut and Mike included:

a)      Normal time of emergence of your signal (considering the relatively good conditions that evening) at QTHs of Mike and Henny, but delayed emergence (delayed by ~ 2 hours) at Hartmut’s QTH

b)      Emergence of Dex’s signal at Mike’s QTH at ~0530 as your signal level was decreasing

I suppose that there are a number of possible explanations for (a) and (b) above that could involve misinterpretation on my part, or system conditions; but on the off chance that some part of (a) and/or (b) result from local propagation characteristics, I thought I’d note the unusual items. 74.54xx kHz grabber images from Mike, Hartmut and others have often shown relatively stable and repeatable signal levels (in periods not indicated as unfavorable by the Dst index), and the two atypical features described in (a) and (b) seemed interesting by comparison.

The SNR values in the attached plot are subjective; I calculated SNR based on estimates of Pd and Pfa over each 30-minute interval on each grabber, with estimates of 30-minute Pd and Pfa based on brightness-weighted pixel states. I doubt that the absolute values of the SNR estimates are any more accurate than +/-3dB, but the relative values between points and between traces may be close enough for qualitative assessments such as in (a) and (b) above.

One attribute not noted in (a) and (b) that seems significant: XRS/4 and XRS/5 signal strengths appear to have nearly intersected, or to have been on a path to intersection prior to XRS/4 switch-off, at Mike’s QTH that morning.

I’m very appreciative of all of the quality data being generated by the XRS/ stations and all of the receiving stations. Even data collected during the dead intervals during the geomagnetic disturbances was fascinating in the perspective of Dst correlations noted by Mike, Jay, Alan and Markus.

73,

Jim AA5BW