[Discuss-gnuradio] A new multi-mode USRP receive demonstration program in CVS

[Johnathan Corgan]

A new program in gnuradio-examples has been checked in that implements a
selectable AM, FM, or WFM (mono) receiver using the USRP.

Below is from usrp_rx_nogui.py:


"""
This example application demostrates receiving and demodulating
different types of signals using the USRP.

A receive chain is built up of the following signal processing
blocks:

USRP  - Daughterboard source generating complex baseband signal.
CHAN  - Low pass filter to select channel bandwidth
RFSQL - RF squelch zeroing output when input power below threshold
AGC   - Automatic gain control leveling signal at [-1.0, +1.0]
DEMOD - Demodulation block appropriate to selected signal type.
        This converts the complex baseband to real audio frequencies,
        and applies an appropriate low pass decimating filter.
CTCSS - Optional tone squelch zeroing output when tone is not present.
RSAMP - Resampler block to convert audio sample rate to user specified
        sound card output rate.
AUDIO - Audio sink for playing final output to speakers.

The following are required command line parameters:

-f FREQ         USRP receive frequency
-m MOD          Modulation type, select from AM, FM, or WFM

The following are optional command line parameters:

-R SUBDEV       Daughterboard specification, defaults to first found
-c FREQ         Calibration offset.  Gets added to receive frequency.
                Defaults to 0.0 Hz.
-g GAIN         Daughterboard gain setting. Defaults to mid-range.
-o RATE         Soundcard output rate. Defaults to 32000. Useful if
                your soundcard only accepts particular sample rates.
-r RFSQL        RF squelch in db. Defaults to -50.0.
-p FREQ         CTCSS frequency.  Opens squelch when tone is present.

Once the program is running, ctrl-break (Ctrl-C) stops operation.

Please see fm_demod.py and am_demod.py for details of the demodulation
blocks.
"""

For example, to receive a NOAA (NBFM) station with all the defaults:

./usrp_rx_nogui.py -f 162.55M -m FM

To receive an aviation band (AM) station with all the defaults:

./usrp_rx_nogui.py -f 120.1M -m AM

To receive an FM broadcast band station (WFM) with all the defaults:

./usrp_rx_nogui.py -f 98.5M -m WFM

To receive a ham radio repeater with a CTCSS tone of 151.4 Hz:

./usrp_rx_nogui.py -f 145.23M -M FM -p 151.4

Enjoy.

-Johnathan, AE6HO