![]() For accurate FSK modulation the transceiver needs a good frequency response extending down towards DC. ![]() The ARM Coretex microcontroller is timed by an accurate clock derived from a TCXO and demodulates incoming FSK from the attached receiver’s discriminator tap or modulates the transmitter by creating FSK symbol by means of varying voltage applied to the FM modulator. The Pi looks after the IP connection (Wi-Fi or Ethernet) and network layer function implementation sending and receiving modulation symbol data via the USB port. ![]() The system components are responsible for different aspects of the modem. The mmdvm is a multi-mode system in that it supports a variety of digital voice modes but our interest here is with its DMR capability. Support for low power hotspot operation based on adapters using the Analog Devices ADF7021 integrated FSK transceiver chip used in most other hotspots is also now available. ![]() Unlike the DV4mini, DVMEGA, and OpenSPOT dongles the MMDVM project is not a product but a small system comprising a Linux platform (often a Raspberry Pi), a small 32-bit ARM Coretex M3 microcontroller, and an analog interface circuit to connect an analog FM transceiver. ![]()
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