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Hi,
I am using an Ettus USRP N210 with a LF RX daughterboard [1] to
*receive* signals.
After having tuned to a frequency of 1 MHz with this call (which I
understand corresponds to a full 'automatic policy' for the tuning):
uhd::tune_request_t frequency{1.0};
uhd::tune_result_t t_res;
t_res = usrp->set_rx_freq(freq, chan);
I display results of the tuning request using 't_res.to_pp_string()'
and get:
Tune Result:
Target RF Freq: 1.000000 (MHz)
Actual RF Freq: 0.000000 (MHz)
Target DSP Freq: -1.000000 (MHz)
Actual DSP Freq: -1.000000 (MHz)
Now, this section of the documentation [2] stipulates:
<<
Note that the meaning of the DSP frequency's sign differs between TX
and RX operations. The target frequency is the result of target_freq =
rf_freq + sign * dsp_freq. For TX, sign is negative, and for RX, sign
is positive.
>>
I'm trying to make sense of these figures. But unless I am mistaken,
applying the formula above with a positive sign (since I am interested
in _receiving_ and have just set the RX frequency) leads to results I
fail to grasp properly:
- with the 'Target' figures: 1 + (-1) = 0
- with the 'Actual' figures: 0 + (-1) = -1
During the same execution, usrp->get_rx_freq() returns a result which
seems compliant to the tuning request: 1000000.000931 Hz.
So my question is: how should the figures found in the 'tune_request_t'
structure be read and understood?
I would be most grateful for any help you could provide.
Kind Regards,
Imad
[1] Details about the hardware I'm using:
$ uhd_usrp_probe
[INFO] [UHD] linux; GNU C++ version 7.3.0; Boost_106501; UHD_3.14.0.0-
229-gc34fa6d8
...
| Device: USRP2 / N-Series Device
| _____________________________________________________
| /
| | Mboard: N210r4
| | hardware: 2577
| | serial: F44F5C
| | FW Version: 12.4
| | FPGA Version: 11.1
...
| | | RX Dboard: A
| | | ID: LF RX (0x000f)
[2]
https://files.ettus.com/manual/structuhd_1_1tune__request__t.html#a616cd26b5d26bfa04909ab2304770492
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