Move USRP LO with USRP sink block?

Is there a setting to move the USRP LO in the SINK block? Not in code,
in
the block, I’m am integrating another developers system and need to use
the
GRC block

On 02/09/2015 11:53 AM, Jon W. wrote:

Is there a setting to move the USRP LO in the SINK block? Not in code,
in the block, I’m am integrating another developers system and need to
use the GRC block


Discuss-gnuradio mailing list
[email protected]
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
I’m afraid you’re going to have to expand on what you mean by the above.

When I transmit a signal at a certain frequency there is a large spike
at
what I have set the center frequency of the USRP. My signal does not
have
this large spike, because it is the LO of the USRP. We take care of this
in
things we write ourselves, but I can’t find the documentation to do it
for
the GRC block. Here is the code I would normally use to tune the LO to
something else, but still have my signal appear at the center frequency
I
would like

usrp::multi_usrp::sptr u2;

  u2 =  usrp::multi_usrp::make(dev_addr_vec[usrpId]);

  uhd::tune_result_t tune_res;

  // tune with lo offset
  offset_freq_Hz = usrpConfig->rx_lo_offset_MHz * 1e6;
  uhd::tune_request_t tune_req(usrpConfig->rx_freq_Hz, 

offset_freq_Hz);

  tune_res = u2->set_rx_freq(tune_req);

There’s a uhd.tune_request() function mapped into Python land, so you
can use the result of that as the “freq” parameter in a UHD sink block.

On 2015-02-10 13:55, Jon W. wrote:

// tune with lo offset
_______________________________________________ Discuss-gnuradio mailing list
[email protected] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
[2] I’m afraid you’re going to have to expand on what you mean by the above.
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio [2]
Links:

Hi Jon,

that documentation can be found in the UHD manual [1] and specifically
in the tune_request_t doxygen [2].

Greetings,
Marcus M.

[1]
http://files.ettus.com/manual/page_general.html#general_tuning_rxchain
[2]
http://files.ettus.com/manual/structuhd_1_1tune__request__t.html#af9d2c5fb89c10024b1acae43e88ebe7f

Right, where is this functionality in the USRP_SINK in GNURadio
companion?
Or do I need to create some kind of python wrapper?

Thanks, I need to be able to do this with the block in Gnu Radio
Companion,
from the GUI, is that possible?

On Tue, Feb 10, 2015 at 1:59 PM, Marcus Müller
[email protected]

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

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.

Greetings,
Marcus M.

Hi John,

I’m a bit confused. You’re using the WBX, correct?
The WBX can not go down to 3.something MHz, that’s outside its frequency
range. You should be getting warnings about that when trying to tune
there; you’re most probably looking at the signal at the lowest
frequency that the WBX can do.

The other things you said were a bit questionable, but I’d prefer to
discuss them when I understand where the signal you’re interested in
actually lies.

Best regards,
Marcus

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