Summer 2008 Issue
Figure 1. The western W3 to DL path.
In his article “Predicting Transatlantic 50-MHz F-Layer Propagation” in the March 1993 issue of QST, Emil Pocock, W3EP, derived a statistical plot that forecasted transatlantic 6-meter propagation from New England to Europe via the F2 region. The plot was based on data for the months of November, December, January, and February around solar maximum at the optimum times of day.
The purpose of this article is to introduce a method to predict 6-meter F2 propagation for any path, for any phase of a solar cycle, for any month, and for any time of day. If you’re a seasoned 6-meter operator, more than likely you won’t need any help with predicting 6-meter F2 propagation. However, if you’re new to 6 meters or in an unfamiliar location, you may find this method useful.
The method will use one of our HF
propagation prediction programs, specifically VOACAP (Voice of America
Coverage Analysis Program), which is the Voice of America version of the
well-respected IONCAP (Ionospheric Communications and Analysis
Prediction) program. For a brief tutorial of VOACAP, including download
instructions, visit <http://mysite.verizon.net/ k9la/id9.html> and read
the file “Downloading and Using VOACAP.”
Since VOACAP is an HF prediction program (2–30 MHz), we suspect it won’t do very well on 6-meter paths. We can verify this by running a prediction from North America to Europe during the good days of November 2001. Then from observations during this period in “The World Above 50 MHZ” column by W3EP in the February 2002 issue of QST, we can evaluate VOACAP’s 6-meter performance. Figure 1 shows the path under analysis.
We’ll use Method 30 in VOACAP at 1600 UTC for a path from western Pennsylvania to Germany. Because our propagation prediction programs were developed based on the correlation between a smoothed solar index (either smoothed solar flux or smoothed sunspot number) and monthly median ionospheric parameters, we’ll run the prediction using the November 2001 smoothed solar flux of 194 (from the plot “ISES Solar Cycle F10.7cm Radio Flux Progression” at <http://www.swpc. noaa.gov/SolarCycle/>.
VOACAP predicts the monthly median MUF (maximum usable frequency) for our W3-to-DL path to be 37.2 MHz (this is the value given in the left-most column of the results). We can determine the distribution about the median MUF by using the tables of MUF variability in our ionospheric literature (for example, in the booklet “Predicting Statistical Performance Indexes for High Frequency Ionospheric Telecommunications Systems,” Technical Report 1-ITSA 1, 1966).
From this we see that on 10 percent of the
days of November 2001 (three days) the actual MUF is predicted to be as
high as 41.3 MHz. This also says the probability of the MUF being high
enough for 50.1 MHz is zero. However, there was 6-meter F2 propagation
in November 2001, as noted in the aforementioned “The World Above 50
MHZ” column, and thus our initial suspicion that VOACAP doesn’t do well
on 6 meters is confirmed.
One problem with VOACAP for 6-meter predictions (and with any of our other HF prediction programs, for that matter) is tied to the solar index used. The use of the heavily-averaged smoothed solar flux value of 194 for our prediction belies the fact that the solar flux was significantly higher right before November 11 through November 19, the period when most of the 6-meter openings occurred. Figure 2 plots the daily solar flux for November 2001.
Thus, it appears that we need a shorter-term
solar flux measurement for input to VOACAP. We could use daily solar
flux, but unfortunately the state of the ionosphere does not correlate
well with daily solar flux. Figure 3 shows this by plotting the daily
MUF over the Goose Bay, Labrador ionosonde (which is along the path from
western Pennsylvania to Germany) and the corresponding daily solar flux
for November 2001.
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