As Project25 has noted, Texarkana, as well as a number of Bowie County agencies, are using
GATRRS.
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Texarkana Police and Fire, as well as Bowie County agencies, and some of the smaller towns dispatched by the county, are also on this system.
There are two sites listed as being in Bowie County. One in Texarkana itself, the other in New Boston.
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It appears that neither site is simulcast, but you would need a scanner capable of handling P25 (digital) trunked systems in order to monitor these talkgroups. These TGIDs are noted as P25 Phase I, so there are a large number of digital scanners available that can monitor the system if they are programmed correctly. You don't need a high end scanner, such as Uniden's SDS series, to monitor this system. Your best choice will depend on what else you want to monitor other than Texarkana. If you can indicate what else you could monitor, as well as whether or not you already have some model of scanner, then we can suggest what models to look at.