Re: [Discuss-gnuradio] Move USRP LO with USRP sink block?

[Marcus Müller]

You can request that UHD tries to get the LO offset you request as close as possible, but because the LO synthesizers used on the USRPs/daughterboards (what are you using, by the way?) can only synthesize a discrete set of frequencies, not everything is possible.
Now, I just realized you tried to tune a daughterboard to 3MHz (I misread and thought you'd try to tune to 3GHz). There's no daughterboard that goes that far down, because that's really just baseband.
So I have to assume that you're using LFRX or BasicRX, which don't have mixers, so the LO frequency is always 0 and the digital shifting is always the center frequency you ask for.

Best regards,
Marcus

On 06/05/2015 12:20 AM, John Petrich wrote:

Marcus,

 

Yes, could you help me with a specific command for the properties field:  I want a rx frequency of 3.545 MHz with an LO offset of 50e3 Hz.

 

Thank you,

John Petrich

 

From: Marcus Müller [mailto:address@hidden]
Sent: Thursday, June 4, 2015 2:41 PM
To: John Petrich; GNURadio Discussion List
Subject: Re: [Discuss-gnuradio] Move USRP LO with USRP sink block? (was: Re: question per your 2/10/15 post on Ruby Forum)

 

Hi John,
I'm a bit confused; which discussion is this from?
Ruby-Forum is not actually the platform we use, they just "mirror" the GNU mailing list archives (I don't really know why they do that -- we don't have anything to do with them). I'd recommend joining that mailing list personally [1].

Regarding your question:
10kHz is very small. Possibly, the closest possible physical LO frequency is still the one you'd have if you didn't shift. Try increasing 10e3 to something that is out of the band that you want to observe; for example, if you're using a sampling rate of 10e6, try 11e6. The only important thing is that the whole observed band stays within the analog bandwidth of your USRP (B2x0) or the daughterboard used (modular USRPs).

Best regards,
Marcus

[1] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

On 06/04/2015 11:26 PM, John Petrich wrote:

Marcus,

 

I cannot get the DC component to shift using this command in the USRP Source block properties:  uhd.tune_request(3.545e6,10e3)  What am I missing?

 

Thank you in advance,

John Petrich

 

Re: Move USRP LO with USRP sink block?

Marcus Müller (Guest)

on 2015-02-10 20:10

Well, you nearly already are doing this!

just use "uhd.tune_request(...,...)" where you'd set the TX frequency

normally in the USRP sink's properties dialog.