Here is the grc file of the NBFM transceiver:
Realising a transceiver does not simply mean combining a receiver and a transmitter. Some additional aspects apply.
Latency of switching RX to TX and vice versa has to be optmized. The throttle block significantly improves switching time.
Handling the "center spike" by the blocks 'Signal Source' and 'Multiply' is much faster than the alternative of applying the 'Frequency Xlating FIR filter', which will otherwise give the same functionality.
The center spike has been shifted to a fixed position at the very edge of the spectrum at 144.00MHz.
I did not find an easy way to completely turn off the transmitter during receive. The settings
- Osmocom sink: RFgain=0, IFgain=0, BBgain=0
- Low pass filter: Gain=0
will drop the power level down to an uncritical level below -60dBm.
73 de John