Thanks for the easy links to Amazon. Very helpful. Being a complete novice with ground based comms for my truck (Im an airline pilot using HF’s across the Atlantic every week) with Midland radio you suggested be able to communicate with guys on the trail using hams and vice versa?
GMRS and ham are two different animals. Usually clubs use one or the other. Many hams (like me) keep both in their vehicle.
GMRS uses discrete frequencies around 462MHz and 467MHz (voice only). Mobile ham is typically ~144MHz or ~440MHz (voice and/or digital), though many of the ham rigs can also receive on the GMRS frequencies, and while not legal according to the FCC's regulations, some ham rigs can also transmit on GMRS frequencies. However, others have pointed out here that legality and enforcement are two different things - not that I'm encouraging anyone to break the law, but in an actual emergency, any usage a licensed ham believes is necessary to save life or limb is explicitly permitted under the FCC regulations.
Both ham and (some) GMRS radios are capable of using repeaters to relay their signal beyond line-of-sight. Here in New Mexico, there are ~28 GMRS repeaters and over 320 ham repeaters. Many of the ham repeaters are additionally linked together, so if you can reach ANY one of them, you can be heard on ALL of them, potentially extending your communication range to hundreds of miles - one can talk to Fort Collins, Colorado from Albuquerque, New Mexico using one of the linked repeater systems. Even with a fairly low power radio, I'm able to reach repeaters ~50miles away. (There are also digital repeaters, that can pass a transmission over the internet and out of another repeater in a very remote location - I've talked to Australia, but that's not as useful for overlanders.
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Both ham and GMRS are available in vehicle mounted units (GMRS typically 15-40 Watts and ham typically 20-100 Watts) or handheld units (aka handy talkies or HTs, around 5 Watts).