On Tue, Dec 8, 2009 at 2:40 PM, Hanno <address@hidden> wrote:
Brian Padalino schrieb:
No need to re-tune as long as you're within 32MHz (maybe 64MHz due to
complex sampling?).
Since you have a good amount of bandwidth to work with at the host,
you could just "hop" at the host level with your samples and a mixer.
Or, if you need more bandwidth, you can put the hopping sequence into
the FPGA going into the DUC and go to a different phase accumulation
based on how many samples have just been transmitted.
Plenty of ways to skin this cat without having to retune as long as
you can fit within the DAC bandwidth.
Brian
Hmm I thought about this before too, but what do you mean with
Since you have a good amount of bandwidth to work with at the host,
you could just "hop" at the host level with your samples and a mixer.
The total amount of bandwidth available to transmit over to the USRP1
over USB is 8MHz, right?
If you went to a USRP2, I think it's 25MHz?
So if you constrained yourself to that bandwidth, you could just drive
a mixer with a list of "offset" frequencies from what you've tuned.
Your baseband signal goes in, and the "offset" signal comes out. That
offset signal is then fed into the modulator and goes out at
Fc+offset.
Just playing with complex phasors and frequency offset, that's all.
If you need more bandwidth than that, just move the list from the host
level to being inside the FPGA. There is a DUC in the USRP1 FPGA
(probably in the USRP2 as well I am guessing?) to compensate for not
being able to tune the synthesizer to the exact frequency (at least I
think that is the reason).
You could have a known hopping pattern or choose your center frequency
such that as you hop, the sample images show up within band (utilize
bandpass sampling here but make sure your images don't fold over a
Nyquist zone).
Hope this clarified things, but I have a feeling it didn't. Sorry. :(
Brian