Greetings to all,
More or less the same question here, plus also a few remarks and
questions for Asshar I suppose.
I sincerely hope that all is well in Hyderabad and that Asshar is
able the pursue his work on the sBITX after his brilliant
presentation last spring.
Many thanks to him for sharing this with us all.
Over the past years I experimented myself a bit with the
quadrature direct conversion architecture, using various micro
controllers: STM32F446, ESP32 and recently RP2040 in a set up with
a WM8731 (running at 8ks/s), a FST3253 and a Si570.? Though all of
this more or less worked, I never succeeded in having an adequate
side band suppression (typically not more than 30dB).? This is of
course related to the rather challenging hardware task of having a
very precise 90¡ã relation between the I and Q signals (of both the
VFO and the audio) and having precisely the same gain on both I
and Q amplifiers.
Asshar's double conversion architecture with one sharp IF filter
at 27/40MHz in hardware and a second at 24kHz implemented in
software is i.m.h.o. absolutely brilliant, as it circumvents all
the above problems.? Also is the idea of performing filtering,
demodulation, etc. in the frequency domain.
This comes at a price however, running the codec at 96ks/s and
performing a 1024 bins floating point FFT every 10ms excludes the
low end micro controllers, even the RP2040 (no FP coprocessor).?
Hence the use of the Raspberry Pi as a computational platform.??
A few questions if I may.?
- Would the sBITX software run in a headless configuration (only
CAT, no GUI) on a Raspberry Pi Zero ? (and obviously without the
WSJT-X application).? I am particularly interested in using the
sBITX in a remote battery operated (= low power) TRX set up.?
- The hardware setup diagram shows a Raduino board connected to
the Raspberry Pi by USB.? Can the Si5351 not be controlled
directly through the I2C bus of the Raspberry Pi ?? It is
otherwise used for the WM8731.?
- The repository on is a bit confusing:?
two libraries for bit banging the I2C bus, tough WiringPi includes
the I2C functionality.? A library for the Si570 seems a bit lost
in this context.?
- The WM8731 codec seems to be setup (sample rate, gain settings,
etc.) by its driver build in Raspbian driver, which is fine I
guess.? Can it be controlled (e.g. gain, microphone input, etc.)
by alsa config ?
- A more elaborate guide to the installation of the various
libraries and the building of the software would be greatly
appreciated.? Is e.g. any flavor of Raspbian ok ??
73 ON4JRT / Jean.
Op 3/07/2021 om 00:15 schreef Peter
McCracken:
Hi Niels,
Did you ever make any progress with this or get a board up and
running ?
Also did you source some 27Mhz crystals, if so which ones did you
go for ?
Thanks!
