Class D 600 Watt Topband Amplifier Mods

After some tests on Topband a few modifications were made. The 40A bridge rectifier failed and was replaced with 50A one mounted on a better heatsink, the problem appears to be the ability to handle the peak repetitive forward current charging the 30mfarrad capacitors -the specs for the rectifier don't show this value - only average forward current i.e. 50A. A front panel transmit/receive switch was also fitted to replace (temporarily) the control from the FT817. The FT817 transmit control line currently does not provide sufficient delay (pretty sure it can be programmed for sufficient lead-in) to ensure the antenna relay is properly made before the amp delivers full power. The final mod was to the microwave oven step/slow start protection circuit. Instead of a 22 ohm series resistor limiting the primary current, the two 50 ohm resistors were connected in series giving 100 ohms which limits the primary inrush current to 2.4 amps (24 amps in the secondary). The protection relay timing capacitor was also increased from 50 microfarrad to 250 microfarrad.

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Digital Bandpass Filter FIR design - Python

The python code generates the Finite Impulse Response (FIR) filter coefficients for a lowpass filter (LPF) at 10 (Hz) cut off using firwin from scipy. A highpass filter is then created by subtracting the lowpass filter output(s) from the output of an allpass filter. To do this the coefficients of the LPF are multiplied by -1 and 1 added to the centre tap (to create the allpass filter with subtraction). A second LPF is then created with a cutoff at 15 (Hz) and the bandpass filter formed by addition of the LPF and HPF coefficients. The program also generates a test sine wave of a given amplitude and power and to this noise from a Normal distribution is added. The graph below shows the signal and nois, and the signal (green) after filtering. The input snr is approximately 3dB. The frequency response below shows the passband centered on 12.5 (Hz), the Nyquist frequency is 50 (Hz). from numpy import cos, sin, pi, absolute, arange from numpy.random import normal fr...

GNU Radio Waterfall and CW Filter

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...

QUISK SDR 40 metre RX

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.

G4AKW

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