Re: [Discuss-gnuradio] Questions regarding the TVRx

[Eric Blossom]

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


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