Re: [Discuss-gnuradio] question about USRP up/downconversion

[Nick Foster]

On Tue, 2011-03-22 at 15:39 +0900, Songsong Gee wrote:
> I have some curiosity about USRP up/downconversion 
> 
> 
> If I have a rectangular pulse train
> and I want to send it with carrier freq. 2.4G
> So I set frequency in USRP block with freq. 2.4G
> 
> 
> Then, my rectangular pulse train is moved to 2.4G band in frequency
> domain?
> In other words, USRP block automatically moves baseband signal to
> carrier frequency? And is it called 'upconversion' ?
> Or, before the USRP block, do I have to multiply a sinusoidal signal
> with freq. 2.4G ?

Whatever frequency you set as the USRP source/sink block frequency is
the baseband frequency. You don't have to do any multiplication.

> 
> 
> In advance, If I have a signal with two main component with freq. 100M
> and 200M
> and USRP carrier freq. is 2.4G,
> Then does this performs FM with freq. 2.5G and 2.6G?

You've got the right idea, but you can't actually do this since you
don't have enough bandwidth to do so. This would require at least 200MHz
of bandwidth, and the USRP2 is capable of 25MHz. If you changed your
example so that you set the USRP to 2.4GHz and then put in sinusoids of
1MHz and 2MHz, you would indeed see 2.401GHz and 2.402GHz.

--n

> 
> 
> I have some difficulties about understanding modulation and carrier
> frequency
> 
> 
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