The pxa1826_cfg.tar.gz is a specially crafted configuration file used to "open-line" or network-unlock routers powered by the Marvell PXA1826 chipset. A network-unlocked router can accept a SIM card from any compatible provider, not just the one it was originally sold for.
What or behavior are you experiencing with the modem?
. It is used to initialize the cellular radio, define network bands (LTE, TD-SCDMA, WCDMA, GSM), and set device-specific identifiers.