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GG56tv 40m Spectrometer
spectrometer is a SDR experiment developed Edson W. R. Pereira,
PY2SDR, located in the city of
Pardinho, Sao Paulo, Brazil. The
system records a 48 kHz segment of the 40m Amateur Radio band using a
quadrature sampling detector, processes the samples using Fourier analysis
and SDR, and presents the results via a web interface.
The spectrometer hardware consists of a
receiver and an inverted-V dipole antenna elevated about 5 meters
above ground (to favour NVIS signals). The software used is a combination
of generic Linux ALSA utilities, DttSP
sdr-core (dttsp-ol version) and
some tools and web software developed by myself for the application. A
block diagram for the system is shown on Figure 1 below.
Figure 1 - Block Diagram
The system dataflow is as follows:
Use and Applications
- Audio samples are captured by the arecord ALSA utility and are stored
in a .wav audio file containing 1 minute of samples recorded at a rate of
48 kilo samples per second using 16 bits per sample.
- The .wav file is then processed by a utility writen in C that performs
Fourier analysis of the samples and saves the power spectrum representation
in a .png file. The results from the FFT are plotted on a spectrogram image
where different color tones between black and white, with intermediate values
in blue, represents different power levels. The software automatically
adjusts the color contrast level to match the highest detected power and the
noise floor. The images are created using the
- The .wav file can be used further as input to the SDR processing software
(sdr-core) that can, by user request, demodulate a segment of the sampled
spectrum. The output of sdr-core is a .wav file that is then converted to
MP3 and is presented to the user for download.
Some suggested uses are:
- Online Spectrum Analyser for measuring and adjusting transmitters and
- Online Radio Analyser for performing qualitative measurements and
monitoring of radio transmissions.
- Panoramic observation of ionosferic propagation of radio signals.
If you have any enhancement suggestions, comments, or alternative uses
for the system, I would be very interested to know and would be glad to
hear from you.
Ex PU2MWD, JF1AFN, 7N4NCL, N1VTN, PU1JTE