Impulse response USRP DAC<->ADC

GNU Radio
1

Hi All,

I connected the DAC of the USRP directly to the ADC (basic db, 50ohm
cable),
2MHz sample-rate. The impulse responses I get are:

h1=[0,-2,2,-7,8,-6,314,479,-47,-161,-124,-103,-79,-63,-50,-39,-29,-23,-17,-1
4,-13,-9,-7,-5,-4,-3,-3,-2,-1,-3,-3];
h2=[0,-1,-1,0,-2,2,22,274,208,-77,-79,-71,-53,-46,-36,-28,-23,-17,-15,-12,-1
0,-7,-5,-4,-4,-3,-4,-2,-2,-2,-1,-2];

Where h1 is with “set_adc_buffer_bypass” and h2 without it. Does this
make
sense ?

BR/
Per

2

Per Z. wrote:

Where h1 is with “set_adc_buffer_bypass” and h2 without it. Does this make
sense ?

Yes, this looks reasonable. You are seeing a hole at DC because of the
low frequency cutoff of the transformers. If you used the LFRX and LFTX
instead of the BasicRX and BasicTX, you wouldn’t see the hole there.

Matt

3

When I changed the base-band frequency of the digital up/down-conversion
from zero to 4MHz the hole disappeared.

4

Per Z. wrote:

When I changed the base-band frequency of the digital up/down-conversion
from zero to 4MHz the hole disappeared.

There is no 4 MHz hole. You are seeing rolloff from the CIC filter on
the TX.

Matt