Re: [Discuss-gnuradio] USRP transient peak from lock, unlock, set decim/freq

[Marcus D. Leech]

On 12/07/2011 1:05 PM, Nick Foster wrote:
> On Tue, 2011-07-12 at 11:07 +0200, Johannes Schmitz wrote:
> > I am getting some kind of very strong transient peak when using lock
> > unlock and changing usrp decimation rate and frequency and in the
> > beginning.
> > Is this a normal behaviour?
> > So each time I reconfigure my system I have to throw away some samples
> > to avoid this peak or am I doing something wrong?
> This is normal behavior. Each time the daughterboard is re-tuned, there
> is a transient as the VCO settles. A smaller (and much shorter)
> transient is expected during rate changes as well due to different
> filters being switched in and out. It's best to throw away the first few
> samples after changing frequency or rate.
>
> --n
Also, there's no reason to lock the flow-graph for frequency changes or 
gain changes (or a bunch of other parametric changes
  within the flow-graph).  I've never had to use lock()/unlock()--I 
understand that they're used during flow-graph topology changes.
  But parametric changes don't require lock()/unlock() at all.

Most modern digital consumer-appliance tuners tend to mute the audio 
during re-tune, precisely because PLL settling takes a finite time,
  and typically produces glitches.

Any real communications system will necessarily have to "cope" with 
glitches on the channel.  Very few RF channels are completely clean
  and free of RFI and other artifacts of nature...