The CRC16 of the AX.25 seems that is too weak for the new
decoding approach and we get many false positives.
Now the AX.25 decoder, makes waits for at least two
occurances of the AX.25 SYNC flag.
This commit adds GRCC into the CMake build system and creates the
executables from the .grc files on demand.
Because there is always the case that the gr-satnogs has not
been installed yet in the system, we still ship the auto-generated
from our side executables. In next releases, during the install
target, the GRCC and the executables generation, will be called
after the gr-satnogs is installed.
The IQ File sink, tried to create the IQ
file even if it was instructed by the user not to
store IQ data. Despite the fact that no data were
written, it could trigger however errors in case
the destination file could not be opened,
eg. due to permissions.
The problem was that the base class tried to
open the file at its contructor. This commit
deals with this issue and the file is created
only if the user specifies that wants the IQ
data to be stored.
This commit adds a generic IQ receiver supporting
arbitrary output sampling rate. It also allows the
user to disable or enable the Doppler correction applied.
The commit also drops the outdated fm_demod flowgraph.
This commit adds a hierarchical block that performs Doppler
compensation and resampling.
Rather than using directly the available Doppler correction blocks,
based on the user parameters of the incoming sampling rate and the
desired target sampling rate, it applies proper decimation on the signal
so the frequency shift to be applied to a smaller sampling rate,
reducing significantly the CPU resources required. At the previous
architecture (gr-satnogs 1.x.x) we used seperate blocks for the doppler
correction and the LO digital shift, operating at the device sampling rate.
These two blocks, performing almost the same operation, contributed to a
30% CPU usage of the overall application. Now the LO is compensated by
the Doppler correction block, taking into account at the same time the
Doppler drift.
After the digital LO shift, the Doppler corrected signal is passed through
an Polyphase Arbitrary Resampler, to match exactly the sampling rate
requested by the user.
Sebastian
Manolis Surligas
Vasilis Tsiligiannis