Laggard wrote:Let's see if I've got this right: If that maximum usable frequency between my radio and say Iran is 15000 KHz, does that mean that signals over 15,000 KHz coming from that area will not propegate?
I found this cool little program that shows the MUF for every area of the world and would like to know if I have the idea right.
Usually, when a MUF (maximum usable frequency) is calculated, it is based on an average. So, let's assume that the program you are using is set to provide MUF's for a 50% reliability. That means that for about half of the month, the actual frequencies that might propagation between you and Iran will be slightly higher (about .08) than your example of 15 MHz, and, for the other 50% of the month, the frequency might be at or slightly lower than 15 MHz. Most programs allow you to change the reliability factor. I usually choose about 85 or 90 - giving me 85% to 90% reliability that the frequency established as the MUF on a given path is usable.
Now, there are other factors that come into play during the propagation of a signal. The MUF assumes that there is no degradation of the ionosphere due to any geomagnetic storms. So, the MUF is typical for days when the Kp index is, say, under 4. Also, it will depend on the antenna used on both ends of the circuit, and the power used for transmission. A 1-watt signal in Iran might "die" before it makes it to your location, even if conditions are "right." A signal of 50 kW, however, will certainly make it if the MUF is right, and the general HF conditions are fair to good.