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 â€˜usrp_fft.pyâ€™ is carried out.

So the ADC is 64MSPS, I donâ€™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 donâ€™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