## Sunday, November 28, 2010

### Lesson 13: General Class Exam Course G3B

Here is the 13th lesson in the General Class License series.  This lesson primarily deals with Maximum Usable Frequency (MUF), Lowest Usable Frequency (LUF), and ionospheric skip.  One of the thrills of the HF bands is that you regularly have the ability to send you signals all over the globe via bounces off various layers of the ionosphere.  This lesson provides some parameters to those skip conditions.

For the purposes of he exam, the MUF and LUF are describing the condition of the ionosphere and how capable it is to bending signals back to earth.  The MUF is the maximum usable frequency that will support communications between two points.  The LUF is the lowest usable frequency that will support communications between two points.  For the questions on the exam, the LUF and MUF are dealing with the HF bands as well as the 6m band.  The closer you are transmitting to the MUF without going over, the better your signal will propagate.  As you decrease in frequency below the MUF, the skip distance becomes less and less.  If you transmit below the LUF, your signal gets absorbed by the ionosphere.

Though the MUF and LUF may seem like opposites, it is possible for the LUF to be a higher frequency than the MUF.  When this happens, all long distance HF propagation is for the most part shut down.

The two numbers (or distances, rather) that you need to memorize are:

-The average distance on the earths surface for a signal skipped off the F2 layer of the ionosphere is 2,500 miles.
-The average distance on the earths surface for a signal skipped off the E layer of the ionosphere is 1,200 miles.

And that's about it.  Please feel free to leave any comments, suggestions, or questions you may have in the comments box below.  Thanks!

73,
Andy
KE4GK