[Discuss-gnuradio] Re: about TVRX board IF frequency

[Matt Ettus]

melanio wrote:
>
> Dears,
>
> In data sheet of Microtune 4937 DI5(or in other doc.), the IF
> frequency of a tuner comes out to 5.75MHz.
>
> But according to it directly measures(pin17,18) with spectrum
> analyzer, the IF frequency is 44MHz.
>

Various versions of the tuner operate on different IF frequencies.  The
one you have is at 44 MHz.

> Moreover, DDC values comes out to -20M if ‘usrp_fft.py’ is carried out.
>
> So the ADC is 64MSPS, I don’t know why DDC is -20M and why IF
> frequency is 44MHz.. is it possible figure?
>
> I think 44MHz is so high(It is in contravention of the Nyquist
> theorem) and I don’t know why DDC is -20M
>
>  
>


If the ADC samples at 64 MHz, Nyquist is 32 MHz.  In a bandpass sampled
system, 44 MHz will appear at 20 MHz.  We set the tuner for -20MHz to
bring that 20 MHz down to zero.

Matt