Questions regarding the TVRx

Hi

I was wondering if anyone could please help me? I’m doing some
measurements on the Microtune Cable modem module. I already modified
the .py file to be able to set the 3 gain stages independently. I am
trying to see how the gains should be set to get an input signal of
2Vp-p to the ADC to be able to use the dynamic range as efficiently
as possible. From what I understand, pins 17 and 18 of the cable
modem module are the outputs that go to the ADC. This is a
differential signal, right? We don’t have a differential probe, so I
am measuring pins 17 and 18 on 2 oscilloscope channels and then
displaying the difference of the two. This should give me the signal
that goes to the ADC, right? I’m inputting a 100MHz sine wave, so
this should be a 43.75MHz sine wave? Somewhere I am doing something
wrong, as this is not what I get. Can anyone who has done something
similar please tell me how to do it?

Then I also have a few questions regarding the module itself. From
what I understand, the signal gets captured, amplified by the RF amp,
mixed down to 43.75MHz, amplified by the IF amp and then sent to the
ADC, right?

Thank you for your help.

Sebastiaan

On Tue, Jul 15, 2008 at 02:46:33PM +0200, Sebastiaan H. wrote:

am measuring pins 17 and 18 on 2 oscilloscope channels and then

Thank you for your help.
Sebastiaan

Hi Sebastian,

Matt’s used three different Microtune modules for the TV RX’s. Below
is a link to the first one he used, along with an app note re noise
figure. The differences between the different modules aren’t that
big, mostly whether they do a second downconversion and the frequency
of the IF. You can figure that stuff out by looking at
gr-usrp/src/db_tv_rx.py

http://comsec.com/usrp/microtune/4937-DI5-3x8899-2.pdf
http://comsec.com/usrp/microtune/NF_tutorial.pdf

Eric

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