Hi All,

I want to know what is the signal coming from the USRP onto the USB bus.

I

know that the received signal is a baseband signal and assuming complex

sampling (I have RFX2400 daughterboards) each complex sample that enters

the

USB bus is the following,

x[i] = (inphase_component) + j (quadrature_component), and

x[i] = m(t)cos( 2*pi*FREQ_OFFSET*t + PHI ) + jm(t)sin(*

2pi*FREQ_OFFSET*t +

PHI ), where m(t), is the actual message signal, FREQ_OFFSET is the

frequency offset, and PHI is the phase.

Is that correct?

Thanks

On 05/29/2011 04:50 PM, John A. wrote:

Is that correct?

Thanks

More or less, yes.

There will be random noise components as well, since this is “real

world”, rather than purely a Matlab simulation

–

Marcus L.

Principal Investigator

Shirleys Bay Radio Astronomy Consortium

Of course that is true. I just wanted to make sure my understanding of

the

whole signal flow in GNU Radio/USRP system was right. The IF, down

coversion

etc stages confused me a bit. I was only interested in what I am getting

on

the USB bus to work with so, I wanted to make sure my understanding of

this

system was right.

Thanks for the reply.

On 05/29/2011 05:17 PM, John A. wrote:

Of course that is true. I just wanted to make sure my understanding of

the whole signal flow in GNU Radio/USRP system was right. The IF, down

coversion etc stages confused me a bit. I was only interested in what

I am getting on the USB bus to work with so, I wanted to make sure my

understanding of this system was right.

Thanks for the reply.

You should perhaps do a literature search on “complex downconverter” or

“quadrature downconverter” and “direct-conversion receiver” to

get more understanding.

With one exception, all of the daughtercards use a direct-conversion

scheme to directly convert from RF to a complex baseband, which

is described mathematically as you’ve shown.

I’m always nervous when I see a purely-mathematical description, because

if you think in terms purely mathematical, without also

considering the very-real, very-practical, you can be in for some

surprises.

–

Marcus L.

Principal Investigator

Shirleys Bay Radio Astronomy Consortium