[This document is part of the help files integrated into the ITS HFBC software package.]

If you are a user of VOACAP, you may have noticed that the old output variable F DAYS has been replaced with MUFDAY. MUFDAY is the fraction of the days of the month that the operating frequency will be below the mode MUF. In other words it is the fraction of days one can expect normal ionospheric reflection for the indicated most reliable mode at that frequency.

F DAYS represented a similar fraction except that it was always based on the circuit MUF mode. For example, if a circuit hour has an indicated circuit MUF of 15 MHz for the 1F2 mode, the value of MUFDAY = F DAYS = 0.50. At 9 MHz, the most reliable mode is the 2F2. Now MUFDAY is .85 meaning that 9MHz can be expected to be below the 2F2 MUF on 85% of the days per month. The old F DAYS, if you could see it, would have a value of .99, meaning that 9 MHz will be below the 1F2 MUF (i.e. 15 MHz) on 99% of the days of the month. It seems to make more sense if the fraction of the days per month is shown for the most reliable mode rather than always for the circuit MUF mode.

In making this change to VOACAP, Don Lucas discovered that the mode MUF calculation for higher order modes is in error in IONCAP. Don made the correction so that MUFDAY is calculated based on the correct mode MUF. However, the error affects the above-the-MUF loss calculations that go into signal power calculation for the higher order modes. This is an error still waiting for funding in order to make the correction!