Can someone explain GMRS vs CB, and the benefits of a fixed mount vs handheld?

[Bmadda]

The point is that you can estimate the likely range in miles of signal travel using formulas. Besides the hardware characteristics, the actual range is highly impacted by a number of factors: modulation type, foliage density, physical obstructions (hills, buildings, etc.), multipath (things the signal bounces off of which creates ghost signal images); you can account for some of that with 'fade margin', which distinguishes how much signal will be lost due to those factors before the communication is interrupted (works for permeable obstructions but not nonpermeable obstructions). A 50W radio outputs 46.99dBm. A 5W radio outputs 36.99dBm. The difference in radiated power off the antenna, accounting for cable/connector loss and antenna gain, and the minimum anticipated signal strength at the receiver is the 'Free Space Loss', which also accounts for higher 22dB typical nearfield radiation loss off the antenna. I made a mistake in the earlier examples and applied too much fade margin, corrected below. Again, this is theoretical, your mileage may vary....
Mobile 50W, 6dB antenna... to handheld

Mobile 50W, 3dB antenna... to handheld

Handheld to handheld

Again, to be fair, I would never expect these ranges unless you are communicating across open water like a lake or a bay or talking to a repeater on a hilltop. On the ground, you'll probably be lucky to get 10 to 15mi because you're unlikely to find a clear line of sight between the radios over longer distances. The radio system is quite capable as you can see; it's the terrain that governs the link. If you were in an airplane talking to other aircraft or ground control, a 50W radio would suffice; but you're not in an airplane...

Right...terrain is EVERYTHING. Interesting situation in my local area, there is a very good, powerful repeater located very close to lake Michigan. I live about 30 miles due west of it, and I can mostly make out transmissions from my house, but lots of interference, and about 50% of the time I can key it up, but not reliably, and there are closer ones to use, so I never use it. GMRS users I have met near the Silver lake sand dunes (Mears MI), say they can hear it loud and clear...Thats roughly 120mi of open water away!

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[Alaska Steve]

Right...terrain is EVERYTHING. Interesting situation in my local area, there is a very good, powerful repeater located very close to lake Michigan. I live about 30 miles due west of it, and I can mostly make out transmissions from my house, but lots of interference, and about 50% of the time I can key it up, but not reliably, and there are closer ones to use, so I never use it. GMRS users I have met near the Silver lake sand dunes (Mears MI), say they can hear it loud and clear...Thats roughly 120mi of open water away!

Great examples….