We'll have to agree to disagree on that Red! 
Why in that case is there no FM skip? FM is also much more affected than AM by Multipaths if I remember correctly, and of course except in line of sight over flat country with no obstacles, Multipaths abound.
Jim
Jim,
It's not the modulation scheme that causes "skip". That's propagation off of ionosphere which is caused by what frequency band you're in. Depending on whether it's day or night, skip will be different. HF is great at bouncing, of skipping, off of the ionosphere to give it distance and make it a good long-haul band. The higher you go in frequency, the more likely it is to go through the ionoshphere and not bounce back to earth. Typically, FM broadcasts are done in the VHF band, which does not skip well and is good for a more line-of-sight type reception only (typically out to about 40-50 miles). Also, AM broadcasts are typically done in the MF band and although not as good as HF for skip, will skip more at night (when the e and f layer of the ionosphere merge), but typically follow the curve of the earth better. Higher line of sight frequencies will multi-path or bounce off of buildings, causing delays in multiple signals to be recieved by the receiver. Sometimes you'll get what seems like skip out of VHF and UHF, but what that is is called "ducting". This is a phenomenum in the atmoshere that creates a virtual waveguide that the signal will travel in and causes it to travel extraordinary distances. Down off the coast of Florida and in the Middle East ducting is fairly common and it it's not uncommon for you to hear a UHF channel travel 150 miles, when typically UHF is no more than, based on antenna height, 15-20 miles.
cheers [smiley=xyxthumbs.gif],
Red
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Topic: CB question (Read 2898 times)