No, not necessarily. There are many things that can influence how far an AM or FM signal will travel. While the transmit power, frequency, receive and transmit antenna, time of day (in some cases) will all affect it one way or another, there are some other circumstances to consider. Waves are not 'distorted or amplified' in the way you might think
a. On freqs starting with the AM broadcast band and going up to about 30 mhz or so, the ionosphere plays a role in how far the signal will propagate. On some AM band frequencies, some stations are actually required to reduce their output power and/or change their antenna orientation at night to protect a nearby user of a same or nearby frequency. Generally speaking, an AM station's 'range' (and I'm deliberately using the term loosely here) is generally greatly reduced during the day, and enhanced at night. This rule is good up to about 9 or 10 mhz or so on HF. Between 10 and 30 mhz or so, daylight is required to propagate a signal successfully (although there are some very special conditions where this rule is bent to a certain degree..)
b. Stations in the FM broadcast band (and even up as far as 800 mhz) can be greatly influenced by weather related events where tropo occurs, or in some cases, where the ionosphere's E region becomes highly ionized and reflects signals hundreds of miles or more (what is commonly referred to as 'E Skip', often written as Es). As the solar activity begins to heat up, it's quite possible that the F2 layer will begin to reflect a signal - and sometimes, in extreme cases, for thousands of miles. For example, the UK used to have a couple of TV audio frequencies in the 42 mhz range or so. I can remember, during the last solar cycle, constructing a 40 mhz ground plane and listening to BBC TV audio on my scanner. This was likely caused by F2 skip, when the flux levels were around 200 or so.
I have described only a few of the possible scenarios - there are several others, much more complex than this, where signals on the AM and FM bands might propagate longer than they usually would. There are many good websites that describe these scenarios in detail - and some get very technical, frankly. If you're really interested in skip like this, there are several clubs (that cater to AM, HF and FM/TV DX) that do a real good job of discussing these situations, and I highly recommend them as an educational experience.
best regards..Mike
