This project is an FM simplex transceiver for liaison communication when engaged in microwave rover activities.  The liaison radio is used to communicate with other microwave stations to help with antenna alignment, ,frequency coordination, and schedule timing.  The frequencies chosen center around the popular US VHF/UHF FM calling frequencies, defaulting at 146.52 MHz.  This transceiver can also be used as a general ham communications FM rig, a basic simplex transceiver.  This transceiver is a good entry level DSP project and useful for club demonstrations of SDR.

The flowgraph depicted in the work space is divided into three general areas: the Control area, the Receiver area, and the Transmitter area.  The DSP is straightforward FM demodulation and modulation, a squelch, and an FFT panadapter to aid in signal finding and tuning.  Frequency changes are accomplished by changing the frequency parameters in the USRP Source and Sink blocks by frequency entries in the Variable block ID: lo_freq.

Simplified VHF FM Simplex Transceiver Flow Graph

When the flowgraph is executed, the Operating GUI appears.  The FM calling frequencies can be selected with the Preset buttons.  Small frequency changes are accomplished via  adjustment of the TUNE slider.  Transmit power can be controlled with the Transmit Power button.

VHF/UHF FM Simplex Transceiver Operating GUI

The .grc file for this project can be downloaded here: VHF-UHF FM Simplex Multi-band Transceiver

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