Thank you very much Josh

but i have another question for more please

What frequency did you tune the basic RX? Perhaps you are seeing an

offset between signal generator and DDC. Do the tones the FFT sink look

to be in the correct positions?

Did you mean the tune frequency in the basic Rx same with the frequency

that i can set in the usrp source block ?

So if the same i set the frequency in the usrp source block(from my

understand is nco frequency ) equal 1.5Mhz

and the tones of the FFT sink seem like the product of the

multiplication of the input signal(1.5Mhz) and nco signal(1.5Mhz)

and showed only the input signal - nco signal ’ s frequency response

and i think it’s correct.

and

i have another question that is the signal that come from usrp source

that show in the scope sink show the I and Q signal but if i connect the

usrp source with the FFT sink it’s show the frequncy response only one

graph So i’m not sure what was the FFT sink show(I and Q , just I or Q

only , or I +Q )

thank you very much for yours advice