gqrx_scan

A scanner to interface with GQRX, based on the remote control tool gqrx-remote

Loops over a list of frequencies in a csv and listens for activity.

Usage:

Import the module, and make a scanner instance:

scanner = gqrx_scan.Scanner(hostname='127.0.0.1', port=7356, wait_time=5, signal_strength=-55)

These are the default arguments in the constructor, which you can modify as you need. The hostname and port are where the scanner connects to GQRX. The wait_time is how long the scanner waits after a signal drops below the threshold before continuing scanning. This is useful if you have dispatch tones before a voice dispatch, for example. The signal_strength field is the strength below which signals are ignored.

Once you have a scanner object, call

scanner.load(freq='freq.csv')

to import the csv into the scanner, and then run

scanner.scan()

The csv file should be of the format

freq, mode, name

where the frequency is in MHz. Specify the mode according to one of the modes in the table below. On the left the is name of the mode, on the right is what you enter in the csv file.

'Narrow FM' : 'FM'
'Demod Off' : 'OFF'
'Raw I/Q'   : 'RAW'
'AM-Sync'   : 'AMS'
'AM'        : 'AM'
'USB'       : 'USB'
'LSB'       : 'LSB'
'WFM (mono)': 'WFM'
'WFM (stereo)' : 'WFM_ST'
'WFM (oirt)': 'WFM_ST_OIRT'
'CW-L'      : 'CWL'
'CW-U'      : 'CWU'

The mode, frequency, and optional tag are displayed in the terminal, along with the time and frequency, when a transmission occurs.

If you store bookmarks in GQRX, you can use those as input to the scanner as well:

scanner.read_bookmarks(path-to-bookmarks)

and again call the scan() method. The bookmarks are stored in \~/.config/gqrx/bookmarks.csv on Linux systems. Sometimes it is worth skipping some bookmarked frequencies. If you change the "Tag" for a bookmark to "skip," the scanner will ignore that frequency. If you change/add/remove a tag while running the scanner, you need to call scanner.read_bookmarks(path-to-bookmarks) again to update the bookmarks.

There's also a way to use the bookmarks to choose what you do and do not want to scan. If we pass a list of strings to scan, the scan command will check if the Tag of each bookmark is in the list. If so, it tunes to that channel, otherwise it skips it. We can assign some frequencies to be in a group called 'Ham' and other frequencies to be in a group called 'Aircraft'. A call of scan(['Ham']) will only scan the frequencies with the 'Ham' tag and will skip the 'Aircraft' tag. If we call scan() without arguments, it will scan all of the frequencies except for those marked 'skip'. We can also call scan(['Ham', 'Aircraft']) to specify more than one tag to scan.

To scan a range of frequencies with a given mode, we can instead use the scan_range method as follows:

scanner.scan_range(minfreq, maxfreq, mode, step=500, save=None)

This loops continuously from minfreq to maxfreq with a step size of step (defaults to 500 Hz) and stops when there is a transmission. As an example, we can scan the US FM broadcast band by way of the command

scanner.scan_range(88.0, 108.0, 'WFM_ST', step=100000)

This will loop over the FM broadcast bands and stop on the first active station. While scanning over a range we may hit interference we do not want to keep waiting on. We can either press Enter and we will increment to the next frequency (current frequency + step) or we can type "block" in the command line. The block command will enter the current frequency and a window around it into an ignore list. The next time we pass near that frequency, we will not stop for any signals. The block command creates an interval of the form [freq-eps, freq+2*B] around the frequency. By default B is 5KHz, which will block an NFM signal. eps is 1KHz to account for squelch's impact on when the signal if first detected. The block intervals are not saved for future usage.

Another feature is to monitor a list of frequencies for recording purposes. Modify the record_freqs.csv file to have the frequency in Hz and the mode in one row for each channel you want to record. Then run the recording scanner as follows:

from gqrx_scan import Scanner
sc = Scanner(signal_strength=-60)
sc.set_record_list("record_freqs.csv")
sc.listen_and_record(time_limit=10)

With a scanner instance, we set the path to the recording frequencies via set_record_list. We then call listen_and_record. The time_limit value is how many seconds we will continue recording after the signal drops below the signal_strength threshold. If no time_limit value is provided then the default is 10 seconds. Sometimes it makes sense to extend this based on the nature of what is being recorded. When we encounter a signal on the record_freqs.csv list, it begins recording the audio output to a .wav file. If the sound from the file is clipping, then adjust the gain down on the audio panel in GQRX (Crtl+A). If you interrupt the scanner while recording, the recording will be stopped.

Make sure you have enabled remote connections in GQRX.

If you would like to contribute, submit a pull request!

TBD:

1. GUI?

2. Ability to add/delete frequencies in the GUI

3. Set signal_strength for each channel

4. Timeout for scan_range (so as not to get stuck on a birdie or a continuous broadcast)

5. Pause scanning from command line