You'd have to look at the detailed specs of the ADF4001 PLL chip that is
used to steer the VCTCXO.
That chip doesn't, as far as I know, have a "reference quality metric"
output, and if it does, UHD doesn't expose it.
On 2017-10-03 11:44, Dario Fertonani via USRP-users wrote:
> I'm testing the behavior of B210-based systems, comparing the performance
> with "internal" and "external" (10 MHz) clock source. Expect for the
> following "is the 10 MHz input actually present" check running when the app
> starts, the two branches share the same code.
>
>> rfBoardPtr->set_clock_source( "external" );
>> sleep( 2 );//give board time to lock
>> if ( rfBoardPtr->get_mboard_sensor( "ref_locked" ).to_bool( ) == false )
>> {
>> throw std::runtime_error( "Unable to find a valid 10 MHz reference signal.
>> Please check that the signal source is properly plugged in." );
>> }
>> rfBoardPtr->set_time_unknown_pps( 0.0 );
>
> Besides that check, is there a way of measuring the quality of the signal via
> (UHD) software API, ideally in a more granular way? The check above "passes"
> even when the input signal is poor, which I see by validating through
> external instruments the quality of the radio signal emitted by the board.
> Ideally, I'd want an API that tells me about such problems before I actually
> check the radio output. To be clear, these are relatively-minor radio issues,
> but are sufficient to reduce the DL peak rate of my LTE system from 150 Mbps
> to 50-100 Mbps with respect to a fully-functional board (either fed by
> "internal" clock source, or by a proper 10 MHz source). The quality of the
> radio output varies noticeably (at least when measured with advanced
> full-stack metrics) when I change the amplitude of the 10 MHz reference,
> which is surprising since said changes are within the recommended range of
> the 10 MHz reference. Could someone please confirm said specs, in terms of
> (peak-to-peak) amplitude
and waveform (square, sine, ...)?
>
> Thanks,
> Dario
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