TVRX module questions

GNU Radio
1

Hi

I need to figure out exactly what is happening to a captured signal
from the moment it enters the TVRX daughtercard to the moment it
enters the PC. At this moment I am conducting some experiments on the
TVRX card. I need to measure the signal that leaves the card and
enters the ADC. My understanding is that pins 17 and 18 of this
module are a differential output. We don’t have a differential probe,
so I’m using CH1-Ch2 and displaying this. My understanding is that if
I input a 100MHZ sine wave to the TVRX card, a 5.75MHZ sine should be
leaving it (we have a 3x7901 tuner module). When I measure this
signal, I just get a random noise signal or something. Could someone
please help me?

Thanks.

Sebastiaan H.

2

Sebastiaan H. wrote:

leaving it (we have a 3x7901 tuner module).
The 3x7901 has a 43.75 MHz IF, not 5.75.

Matt

3

Matt

My DSPing is a bit rusty. With the TVRX card, we send -20MHz to the
DDC. Is this because of 44-64 MHz? The code where the actual FPGA
register gets written is in usrp_standard.cc? Here is a function
called compute_fpga_freq_control_word which takes the -20MHz and
returns 2952790016 which is 10110000000000000000000000000000 in
binary. So for a DDC value of -20MHz, is that the value that gets
written to the FR_RX_FREQ_0 register? What gets written to
FR_RX_PHASE_0? Just zero? I’m just trying to figure out how the
cordic and phase accumulator parts are implemented.

Thanks a lot.

Sebastiaan

4

On Tue, Aug 26, 2008 at 10:54:24PM +0200, Sebastiaan H. wrote:

Matt

My DSPing is a bit rusty. With the TVRX card, we send -20MHz to the
DDC. Is this because of 44-64 MHz? The code where the actual FPGA
register gets written is in usrp_standard.cc?

Clue: it’s called _write_fpga_reg

Please take a look at usrp_standard.h and usrp_basic.h. They define
the C++ inteface. If you want to see how it works, take a look in
usrp_standard.cc and usrp_basic.cc

Eric