G4AKW

To test the previous GNU radio apps and evaluate the linux SDR QUISK software, the following 7MHz SDR was quickly assembled from available parts.  The heart of the hardware is the modulator section of a Marconi QPSK modem using Watkins Johnson M6E mixers with a 90 deg phase shift circuit modified for the xtal frequency of 7035kHz. Using the Softrock .quisk_conf.py file for QUISK with: fixed_vfo_freq = 7035000        sample_rate = 96000 The following daytime spectrograph was obtained on 40 metres. The SDR hardware (90% not used, including the 741 or TL081 op amps as they were noisy + insufficient gain-BW). The PC was a Toshiba Satellite L650 laptop with Ubuntu 11.10 OS.

The following GNU radio application adds a waterfall spectrogram to the previous CW filter program. The plot show 4 CW signals in the audio band (lower sideband) at 7023 kHz. The 700Hz signal is filtered and output to the laptop headphones by the CW bandpass filter. The frequency display is shown after the script which is as follows: #!/usr/bin/env python from gnuradio import gr from gnuradio import audio from lpf_bpf_class import Bandpass from gnuradio.qtgui import qtgui from PyQt4 import QtGui import sys, sip     class cw_filter(gr.top_block):     def __init__(self):         gr.top_block.__init__(self)           sample_rate = 44100         out_rate = 8000         kaiser = Bandpass()         cw_flr = gr.fir_filter_fff(1, kaiser.bpftaps)         decimate = int...

An alternative to the Collins 300 Hz CW filter for the FT817 (well not really - that combination is excellent for CW and much better performance than many more expensive radios - but this is an excellent sw alternative) is this simple GNU Radio Python application which uses the Kaiser CW bandpass FIR filter below. The audio output is connected to the microphone input of a Ubuntu 11.10, 64bit OS on a Toshiba Satellite L650 laptop. Output is from the laptop headphone socket. Python code is as follows: #!/usr/bin/env python #------------------------------------------------------------------------------------ # Program uses the (previous) Python Bandpass filter # module to provide the Kaiser bandpass filter taps. # Mic input, cw filter, gain adjust and headphone    # blocks are cascaded.                               ...

This Python module defines a Waveform class with methods sinewave and noise. Sinewave generates a specified frequency and noise generates samples with specified standard deviation. The constructor requires the duration for both methods to be specified. Class variables are the sampling rate and the number of channels. The packed strings and the signal and noise lists are available. main() adds these and uses Bandpass (from bpf_class - Kaiser window response above) to filter the unpacked samples, using lfilter from audioop. Audio before and after filtering is played and recorded to file. #!/usr/bin/python import wave, struct, math, audioop from alsaaudio import * import signal, sys, getopt from numpy.random import normal from scipy.signal import lfilter from bpf_class import Bandpass class Waveform:     " Waveform Class Generates different waveforms with duration (Sec) length "     def __init__(self, duration):      ...