Danny: While technologically feasible (but perhaps commercial not feasible), current FCC Part 95 regulations are generally interpreted to not allow certification for a GMRS device that can also transmit outside the GMRS channels.
This topic comes up quite frequently about why GMRS devices do not include the license free MURS channels.
From a portability standpoint, the FRS & GMRS radios are smaller than the CD handhelds have historically been. And because they operate in the UHF band their antennas are naturally much smaller.
FRS and GMRS both use FM modulation which means that atmospheric static is not introduced into the audio. CB(CBRS) using AM, USB, LSB. FM has recently been approved by the FCC for use in the CBRS, so in time that difference will become moot.
FRS and GMRS hardware supports squelch codes (CTCSS & DCS) that give you and your group the ability to prevent the squelch on your radios from opening except when a transmitter using that code transmits. So if you are on a camping trip and your family all uses CTCSS 67.0, you will only hear radios that use that code.
FRS and GMRS are not subjected to the gross degree of daily signal propagation changes that affect your range and the ability to communicate locally as CB is. Don’t expect skip to suddenly permit you to talk to Texas from New York because of temporarily atmospheric condition change. But you may experience conditions were perhaps you can talk another town or two away.
FRS and GMRS radios can mostly interoperate because they share 22 or 30 frequencies in common.
GMRS radios are permitted to use wide-band modulation, which can give some GMRS radios an audio quality advantage over FRS. FRS is limited to narrow-band modulation.
GMRS requires a FCC license whereas CBRS and FRS do not.
The GMRS service permits use of radios up to 50 watts. FRS maxes out at 2 and CBRS maxes out at 4.
The GMRS allows for the use of repeaters. Repeaters make it to possible to increase the usable coverage range, most notably when the repeater is installed in a prime high location. It is not uncommon to have repeaters that cover an entire City, even some that will make it possible for two handhelds 40 miles and more apart to communicate.
A GMRS license gives you the permission you need to put up and operate your own repeater.
Antennas for GMRS do not have the 20’ above building or tree rule that the CBRS is subjected to. Instead, height limit rules are the same as for Cell Towers, TV Towers and other tall structures where the FAA rules dominate. If you can afford to put up a 200’ tower and get approved to do so from your local AHJ you can put it up.
Regarding hardware. FCC rules require the use of part 95 certified hardware for CBRS, FRS and GMRS. Each service has its own set of technical certification criteria. I know of no equipment that is dual-service certified. This does not mean there is not hardware that can be modified to operate on two or more services, just that doing so violates your authority to use it. Many, including some members of this forum, choose to operate outside the rules.
GMRS is short range, line-of-sight communications but has a higher power output than CB. GMRS is also FM where CB is AM so the messages are much clearer. GMRS is able to use repeaters that improve the range and can be connected to form networks. Because the frequencies for CB are around 27 MHz and GMRS is in the 460 MHz area the two can't be combined into a single unit.
