I´m studying the Gnu Radio NTSC processing, by the way to know the
processing itself and as a previous work in direction to HDTV signal
processing, while we don´t have HDTV broadcast signal in BrasÃlia.
I worked with the usrp_tv_rcv.py code, using TVRX and BasicRX daughter
boards. From what I could see, I concluded about the project current
status, and I would like to confirm this with you. I wonder if someone
could help me.
The implementation, as it is concerned with the main properties of
NTSC signal (chrominance, luminance and synchronization), just works
with the luminance. Is it right? From what I found out, Daniel G. is
working in an implementation of synchronization, but I couldn´t run his
application. And Prateek have been working with chrominance, in matlab,
but doesn´t have a python version. Is it right? Does anyone know any
other work related to implementation of chrominance and synchronization?
From the luminance, that is working, I observed that the main blocks
implemented in Gnu Radio are:
gr.agc_cc: it modifies the input signal gain depending on the
daughter-board that is used (BasicRX and TVRX). When BasicRX is
selected, the gain ranges from 0 to 20 dB. Using TVRX the gain ranges
from 0 to 115 dB.
gr.complex_to_mag: the AM demodulator deals with a stream of complex
samples giving an 1-to-1 output stream of floating points. This
demodulated signal is received by filters varying from 0 to 1,5 Mhz and
from 0 to 0,5 Mhz, with the aim to eliminate sub-products of the
demodulation of the I signal above of 1,5 MHz and demodulation
sub-products of the Q signal above of 0,5 MHz.
gr.add_const_ff: it forces the increase of the black levels in the
image.
gr.multiply_const_ff: the I inversor supplies two I signals dephased
of 180º, that is +I and -I. The Q inversor also supplies two Q signals
with a difference between them of 180º.
Is it right? Does anyone know any other project that decodes NTSC
signals in software?
I would appreciate some help I can get. Thanks.
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I worked with the usrp_tv_rcv.py code, using TVRX
and BasicRX daughter boards. From what I could see,
I concluded about the project current status, and I
would like to confirm this with you. I wonder if
someone could help me.
I don’t understand what you are asking. What did you
conclude? What do you need help with? What do you need
confirmation on? Perhaps we can talk off list (in
spanish).
The implementation, as it is concerned with the
main properties of NTSC signal (chrominance,
luminance and synchronization), just works with the
luminance. Is it right?
The script you are talking about is trying to
implement a black and white television. It is by
definition luminance only.
From what I found out,
Daniel G. is working in an implementation of
synchronization
I did write a couple of different versions of the sync
detector. Each of them had its own problems.
but I couldn´t run his application.
Why could you not run it? Did it compile? Does they
example run and you get no output (ie black screen)?
What was the compile error or program output on the
console?
What did you use for a signal? Was it an antenna? Did
you use a cable television signal? Did you use a
modulated output from a VCR or similar device?
And Prateek have been working with chrominance, in
matlab, but doesn´t have a python version. Is it
right? Does anyone know any other work related to
implementation of chrominance and synchronization?
You may have some trouble using the MATLAB based
approach Prateek used for chrominance detection; it is
not easily ported to GNU Radio as a block. You must
reliably detect the phase of the chroma burst for
every line. There may already be a PLL block in GNU
Radio but I don’t know what it is called.
stream of floating points. This demodulated signal
difference between them of 180º.
You’ve got the main idea down well except for the
filtering part. Your explanation is confusing.