Glad to hear it working. One question, can the hackrf be used to cover the range, or are two RTL's needed for the following of the control channel? I'll try to set this up for my area and see what happens soon. Thanks.
Missed this question from earlier, but figured it still needed an answer...
OP25's smartnet implementation monitors the trunking control channel continuously because there are situations when it cannot reliably determine that a call is ending (e.g. analog), nor detect the presence of priority traffic which should preempt a call in progress. For this to take place, the application needs at least 2 "channels" defined in the cfg.json file - one dedicated to the 3600bps FSK control channel and the other to the P25CAI (or analog) voice channel. In the op25 world, 'channels' are an entirely software DSP construct comprising of an IF mixer, filtering, demodulation, timing recovery and frame reassembly. Raw samples go in one end of the flowgraph and call-related signaling + decoded audio come out the other.
Each op25 'channel' needs to be fed an appropriate signal source from the tuner hardware. If your tuner has a large enough sample rate you can "park" it on an appropriate frequency (i.e. setting tunable=false) and share it among several 'channels'. If however the tuner only has a small sample rate (e.g. RTL devices) you can dedicate a tuner device to each channel and allow the channels to tune their devices as needed. There are pros and cons of each approach; using wide bandwidth tuners cuts down on the number of antennas and quantity of physical hardware, but it (significantly) increases CPU loading due to increased volume of data being moved over USB plus added computational cost of mixing/filtering higher data rates. Using multiple low-rate sdr devices cuts down on CPU utilization but requires more antennas, incurs higher power consumption and occupies more physical usb ports.
TLDR; yes you can use Hack RF (or Airspy, or anything else supported by gnuradio) if it covers the entire spectrum used by the trunking system you need to monitor.
