These scripts are designed to work in Python 3 preferably with version 3.6 or higher. Dependencies are installed with pip in a virtual environment. The sequence of operations is the following:

virtualenv -p /usr/bin/python3 venv # Create virtual environment
. ./venv/bin/activate               # Activate virtual environment
pip install -r requirements.txt     # Install requirements

freqtracking.py

This script is used to achieve frequency tracking with the FreqTracker plugin. Ideally you would start it before connecting the Frequency Tracker plugin in SDRangel. It works continuously (daemon style) until stop via Ctl-C.

Options are:

-h or --help show help message and exit
-A or --address listening address (default 0.0.0.0)
-P or --port listening port (default 8888)
-a or --address-sdr SDRangel REST API address (defaults to calling address)
-p or --port-sdr SDRangel REST API port (default 8091)

With default options (no parameters) it will listen on all available interfaces including loopback at 127.0.0.1 and at port 8888. It will identify the SDRangel API address with the first request from SDRangel and connect back at port 8091.

Normal sequence of operations:

Start freqtracking.py in a terminal
In SDRangel connect the Frequency Tracker plugin by clicking on the grey square at the left of the top bar of the Frequency Tracker GUI. It opens the channel settings dialog. Check the 'Reverse API' box. Next to this box is the address and port at which the channel will be connected. If you use the defaults for freqtracking.py you may leave it as it is else you have to adjust it to the address and port of freqtracking.py (options -A and -P).
In the same manner connect the channel you want to be controlled by freqtracking.py. You may connect any number of channels like this. When a channel is removed freqtracking.py will automatically remove it from its list at the first attempt to synchronize that will fail.

ptt_active.py

PTT (Push To Talk) actively listening system. For a pair of given device set indexes it actively listens to start and stop commands on the corresponding devices to swich over to the other

Options are:

-h or --help show help message and exit
-A or --address listening IP address. Default 0.0.0.0 (all interfaces)
-P or --port listening port. Default 8000
-p or --port-sdr SDRangel instance REST API listening port. Default 8091
-l or --link Pair of indexes of the device sets to link. Default 0 1
-d or --delay Switch over delay in seconds. Default 1
-f or --freq-sync Synchronize devices center frequencies

Normal sequence of operations:

In this example we have a Rx device on index 0 and a Tx device on index 1. All settings are assumed to be the default settings.

Start ptt_active.py in a terminal
On the Rx device right click on the start/stop button and activate reverse API at address 127.0.0.1 port 8000 (default)
On the Tx device right click on the start/stop button and activate reverse API at address 127.0.0.1 port 8000 (default)
Start the Rx or Tx device
Stop the running device (Rx or Tx) this will switch over automatically to the other

Important: you should initiate switch over by stopping the active device and not by starting the other.