Winter 2007 Issue

Inferring 6-meter Propagation Modes
from Es and F2 Probabilities

Not infrequently, when a long-distance QSO takes place the question is asked,
“Is the propagation multi-hop sporadic-E or is it F2?” Here K9LA looks at the evidence for a series of QSOs between J68AS and Europe to determine the answer to this question.

By Carl Luetzelschwab, K9LA

Figure 1. J68AS 6-meter EU QSOs versus time of day.

In the summer of 2005, Scott, N9AG, operated as J68AS from St. Lucia. From June 23 through July 2 he made 382 QSOs with Europe on 6 meters. He said almost everyone believed this to be propagation via three- or four-hop Es (sporadic-E). Let’s try to confirm this with our knowledge of the statistical pattern of Es. If we don’t succeed, we’ll look at other possibilities.

QSO Data

The most productive day was June 29 with almost 40% of the QSOs made on that date. The second most productive day was July 1 with almost 20% of the QSOs made that day. July 2 took third place with just over 10% of the QSOs made on that day.
Figure 1 is a plot of the 6-meter EU QSOs for all the days when J68AS was active. In essence, figure 1 is a probability distribution, with the highest probability of 6-meter J6-to-EU QSOs centered on 1900 UTC for the late June through early July 2005 time period. (The individual days cited in the previous paragraph follow the same general pattern as figure 1.) The question we’ll try to answer is “Does the statistical pattern of Es between J6 and EU match the statistical pattern of the actual QSOs?”

Es Methodology

To determine the statistical pattern of Es propagation between J6 and EU, we’ll use the plot of 50-MHz Es probabilities from the USAF Handbook of Geophysics.1 Figure 2 shows this plot.
The plot gives the probability of 50-MHz Es for all months versus local time over a two-year period and is applicable to mid latitudes (roughly 30 to 60 degrees). The contour lines are percentages. For example, using the left-most data, the probability of 50-MHz Es at the beginning of June at 1 PM local time is about 45 percent. The term local time refers to the midpoint of the path. Thus, we need to know the local time of the mid-point of each hop along the J6-to-EU path.

Es Analysis

For the analysis, we’ll use a path between J6 and HB (7283 km). We’ll assume this is a four-hop path (each hop is 1820 km). This defines where the apogees (and mid-points) of the four hops encountered Es clouds: at 55°W longitude, at 41°W longitude, at 24°W longitude, and at 4°W longitude. Next the local times at these four encounter points were determined, and the left-most data of figure 2 for the 1400 to 2200 UTC period was used for probabilities. The results of this exercise are in Table 1.

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