LO of the USRP2 motherboard

GNU Radio
1

Hi,

I have an easy question.
When I use my basic T/Rx daughterboards I can tune the receiver to an
specific frequency. Since the basic T/Rx doesn’t have any LO, I would
like
to know where is physically that LO in the USRP2 motherboard. I cannot
find
anything in the schematics. Where is it? Is that LO the one which
translates
from IF (coming from the daughterboards) to real base band?

Thanks in advance,
Jorge

2

On 11/10/2010 02:20 AM, Jorge M. wrote:

Thanks in advance,
Jorge

There is no “LO”, per-se on the USRP2 motherboard, only the various
digital clocks used by
parts on the motherboard, including the ADCs/DACs, and the FPGA.

When you’re using a BASIC_RX/LF_RX and you “tune”, the FPGA uses a DDC
(Digital Downconverter)
to digitally downconvert your desired frequency range to baseband. On
the USRP2, the
BASIC_RX or LF_RX is sampled at 100MHz, so the FPGA “sees” from
roughly DC to roughly
50MHz. Within that range, the FPGA DDC converts whatever you ask it
to into a complex
baseband, which is what the host computer sees.

–
Principal Investigator
Shirleys Bay Radio Astronomy Consortium