I&Q Sampling

GNU Radio
1

How does the USRP do its quadrature sampling??

There seems to be many differing methods of achieving this. Some suggest
the
the ADC’s are off set by 90 deg, others that the samples are multiplied
by a
series of 0,1,0.-1 and 1,0,-1,0 (which seems a waste of samples).

Interested to know…

Paul

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2

paul munro wrote:

How does the USRP do its quadrature sampling??

There seems to be many differing methods of achieving this. Some
suggest the the ADC’s are off set by 90 deg,

There are 2 ADCs, one samples the I channel, one samples the Q channel.
The

others that the samples are multiplied by a series of 0,1,0.-1 and
1,0,-1,0 (which seems a waste of samples).

This is a way of using one adc to sample a real bandpass signal and then
translate it to complex baseband.

Matt

3

Am just looking at the data sheet for the ADC’s now and noticed the on
chip
Hilbert filter…

Cheers

There seems to be many differing methods of achieving this. Some

Matt

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4

paul munro wrote:

Am just looking at the data sheet for the ADC’s now and noticed the on
chip Hilbert filter…

We don’t use that

5

So is the signal multiplied by sin and cos before the ADCs then?? How do
you
determine the the I & Q channels??

chip Hilbert filter…

We don’t use that

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6

paul munro wrote:

So is the signal multiplied by sin and cos before the ADCs then?? How
do you determine the the I & Q channels??

Yes, on the daughterboards which use quadrature sampling. This is part
of the quadrature downconverters.

Matt