This project is a NBFM 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 and frequency coordination.  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 NBFM rig, a basic ‘hand held’ transceiver.

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 NBFM 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.

NBFM Simplex VHF Transceiver Flowgraph

When the flowgraph is executed, the Operating GUI appears.  Frequency changes are accomplished using the Tune buttons in either 10 or 20 kHz increments.  Other FM calling frequencies can be selected with the Preset buttons.  Transmit power can be controlled with the Transmit Power button.

NBFM VHF Simplex Transceiver Operating GUI centered on 146.52 MHz

The .grc file for this project can be downloaded here:  NBFM Simplex Transceiver.grc