Friday, January 5, 2018

Getting the best operating frequency from VOACAP P2P predictions

Updated Jan 6, 2018: Primary, Secondary and Tertiary Frequencies reported.

I am happy to introduce a new functionality at the VOACAP Online P2P (point-to-point) HF propagation prediction service (, namely assessment of the Best Operating Frequencies for every hour of the day for the circuit chosen. This means that all ham radio bands are being considered and, after a careful evaluation, the three best bands will be displayed, together with some VOACAP prediction data.

To use the new service, just click on the new button labeled "Best FREQ", located just below the graphs on the front page.

On the output page, the best operating frequencies can be found in the rightenmost columns: FREQ, FREQ2, and FREQ3. On the left, you will have the UTC hours from 1 to 24. And the other columns from left to right are as follows:

  • SDBW (or Signal Power at the receiver): the dBW (the strength of a signal expressed in decibels relative to one watt) value that can be maintained on 50% of the days (ie. on 15 days) in the month. The S-Meter Signal Strength is displayed in parentheses after the dBW value.
  • REL (or Circuit Reliability): percentage of days in the month when the SNR value will equal to or exceed the REQ.SNR (the threshold value for the given transmit mode); for example, the threshold value (= REQ.SNR) for CW is 24 (dB-Hz)
  • SNR (or Signal-to-Noise Ratio): the median dB-Hz value that can be maintained on 50% of the days (ie. on 15 days) in the month. So, if the SNR value is lower than the threshold or REQ.SNR value for a mode (CW = 24, SSB = 38, AM = 49, etc.), then not so great propagation may be expected at all times.
  • MUFday: percentage of the days in a month at that hour will be below the predicted MUF (Median Maximum Usable Frequency) for the most reliable mode (MRM).
  • FOT (or Frequency of Optimum Traffic): also known as the Optimum Working Frequency for the hourly MOF (median maximum observed frequency) distribution. At the FOT, communication can be supported on 90% of the days (27 days) in the month.
  • MUF (or Median Maximum Usable Frequency): the median maximum usable frequency for a given ionospheric path, month, SSN and hour. On each day of the month at this hour, there is a maximum observed frequency (MOF) for a mode. The median of this distribution is called the MUF. Therefore, here MUF is not the maximum usable frequency in terms of communications. In other words, the MUF is the frequency for which ionospheric support is predicted on 50% of the days of the month, ie. 15 days out of 30 days.
  • HPF (or Highest Possible Frequency): at the HPF, communication can be supported on 10% of the days (3 days) in the month.

The best operating frequencies from Bouvet to my location on February 2018.
Primary = Best FREQ, Secondary = Second Best FREQ, Tertiary = Third Best FREQ

Now, three Best Frequencies are being reported in the output. The SDBW, REL, SNR and MUFday values are reported for the Best Frequency (FREQ) only. In many cases, the Best and Second Best Frequency can be quite equal in performance so it can be hard to tell which one is actually better. However, on the other hand, the Third Best can sometimes be just a theoretical (or even an impossible) choice in practice.

It should be noted, though, that FOT, MUF and HPF cannot be used alone for reliable propagation predictions. The best predictions consider Signal Power, Circuit Reliability, and Signal-to-Noise Ratio values. And this is also what the assessment of the best operating frequency for each hour is based on.

Please be warned, though, that, as a consequence, there can be hours with the "best" operating frequency which does not, in reality, support any communication! The reason can be that the Signal Power, or Circuit Reliability, or Signal-to-Noise Ratio are too low at that hour.

In order to indicate that there can be problems with the best operating frequency given, there can be three signs after the Best Frequency (FREQ): - (minus), + (plus), or * (star). The minus sign means that the Signal-to-Noise Ratio predicted is below zero (i.e., a negative value); the plus sign means the REL value is below 10% but the median Signal Power is still barely above the noise; the star sign means that the REL value is below 10% and the median Signal Power is also more or less under the noise.

The minus, plus and star signs will be applied to the Best Frequency only. So, if the Best Frequency will be flagged with any of these signs, please note that the second best or the third best frequency will not be any better in performance but likely much worse.