MUF. Maximum Usable Frequency

 This is a real time MUF chart. The numbers in the circles indicate the highest frequency that will refract a radio wave for a 3000 KM or 1900 mile path.  If we want to work 3000KM then we should use a frequency at or below the MUF at the midpoint. On the map below we see that the MUF at the midpoint between Virginia and California is above 21 MHz. The mid point is actually around 30 MHz. This means we can be pretty sure to be able to make a contact out to 3000 KM on probably both 21 and 28 MHz.  Since California is a bit over 3000 KM the single hop angle will be lower than the angle needed for 3000 KM.  This is the reason that you can almost always work longer than 3000 KM at the MUF for 3000 KM and usually not closer than 3000 KM. 

I have drawn two lines drawn on the indicating where I was heard on 21 MHz at the same time I copied the MAP. I was heard in both California and Europe on 21 MHz, but I was only heard in Europe on 28 MHz.   Here is a link for the map:  

Realtime MUF map

  












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