Thursday, July 13, 2017

Adding MUFday to the equation

I have been further re-factoring the code that produces the VOACAP HF propagation prediction in table format. Such tables are available e.g. on the VOACAP Point-to-Point page (www.voacap.com/p2p/index.html > All-year prediction) and on VOACAP DX Charts (www.voacap.com/dx.html) or on VOACAP Propagation Planner (www.voacap.com/planner.html). The re-factored code has made it possible for me to add the MUFday parameter to the predictions. And it's a great enhancement, making the high-band predictions even more realistic. Be warned that the 24-hour prediction wheel I use on the VOACAP P2P front page is now "out-of-date" on Above-the-MUF frequencies!

So, with the introduction of MUFday in all assessments, there will be more gray cells in the prediction tables from now on. 

On lower frequencies, the color of gray does not indicate any probability value, in contrast to all other colors used. Instead, gray shows that, although VOACAP does not predict any probability for that specific hour (R=0% in the popup window), some signal power (S in the pop-up window) has been predicted which may translate into workable conditions. So, in a sense, gray indicates "a gray area" where QSOs may be possible.

On higher frequencies, typically on Above-the-MUF frequencies, the color of gray is a sign of extremely poor probabilities. These are actually cases where VOACAP predicts positive REL values but unfortunately VOACAP does not know what's really happening up there. If you take a closer look at the values reported in the pop-up window over the cell (the R, S and M values), the S (Signal Power) value can be very low (e.g. -164 and below which means that there is hardly any signal in the noise).

Frankly, I should have implemented the MUFday assessment much earlier. Let me explain the nature of MUFday as concretely as possible. The value of the MUFday is the fraction of the days in a month at that hour that the operating frequency is below the MUF for the most reliable mode (that is, the mode with the highest reliability of meeting the required Signal-to-Noise Ratio, or SNR). So, on higher frequencies, I have now set the threshold to 10% for MUFday in my assessments. This means that if the MUFday value is less than 10% (or less than 3 days), then the frequency hour cell will be colored gray. And it's totally ok, as this actually means that for more than 90% of the days in a month, QSOs are likely not to happen. The odds are pretty poor.

At 12 UTC on 10 Meters in February 2018 (from OH6 to 3Y0Z), VOACAP says that the REL (R or the probability for a QSO) is a good 21%! However, the Signal Power (S) is -173, way down in the noise. And what is more, the MUFday (M) is a mere 5%. So, the verdict is that there is only the slightest chance (frankly, if any) that QSOs can happen on 10 Meters with the power and antenna chosen. Therefore, the cell is rightfully colored as gray.

Recapping the R, S and M values


As you know, all table charts are interactive: if you hover your mouse over table cells, you will see a pop-up text, now showing three parameter values: R, S and M.

The R is VOACAP's REL or QSO probability in percentages, and the S is VOACAP's S DBW or Signal Power value in dBW. For instance, the signal power value of -164 can be considered to be on the verge of the noise in remote, extremely low-noise locations whereas the S DBW value of -93 corresponds to S9 on the S meter. Read more about translating the signal power values (S DBW) into S-meter values here: http://www.voacap.com/s-meter.html.

And finally, the new M parameter is VOACAP's MUFday value in percentages, indicating the probability for the operating frequency on that hour being BELOW the median MUF calculated.

All in all, MUFday is a much-anticipated parameter to give the wild REL values on Above-the-MUF frequencies a more realistic interpretation.

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