Re: [Discuss-gnuradio] USRP LO Relocation Latency

[Josh Blum]

On 09/26/2012 01:00 PM, Vincenzo Pellegrini wrote:
> Dear gr / USRP fellows,
> 
> I'm currently experimenting with USRP B100 Local Oscillator relocation time.
> I've done some experiments on the RX path by tuning towards and away from
> an OFDM beacon signal.
> 
> I have flushed into the received signal some recognizable "relocation
> marks" which allowed me to analyze the
> received signal integrity in the temporal vicinity of the relocation
> instant.
> 
> It looks like the LO responds to the steering command in some milliseconds
> to about two tens of millisecs,
> still "artifacts" such as unsuppressed, dominant carrier or unstable gain
> remain there for some hundreds of millisecs.
> 
> I saw that the wiki states "perhaps a second" as the LO settling time.
> But can anybody confirm the above behaviour analysis ?

It depends on the daughterboard. SBX and WBX have a worst case settling
time of about 300us according to the ADI docs.

You should also be able to schedule tuning through time commands so that
the window of "interruption" is explicitly between time X and X + 300us.

Here is some psudo code involving using timed commands to tune:
http://files.ettus.com/uhd_docs/manual/html/sync.html#align-los-in-the-front-end-sbx-wbx-n-series


-josh