[USRP-users] signal stability at beginning of streaming
Marcus D. Leech
mleech at ripnet.com
Wed Oct 7 09:24:18 EDT 2015
On 10/07/2015 02:19 AM, Francois Quitin via USRP-users wrote:
> Dear all,
> I’m using a USRP-N210 with a RFX2400 daughterboard, and when I
> initially start streaming I see the amplitude of the I and Q
> components first saturating before they reach a stable level (see
> attached image, I should be receiving only noise).
> I don’t observe this behavior with the WBX daughterboard, so I’ll
> assume it’s some of the amplifiers stabilizing initially? Is there any
> way to avoid this behavior in the RFX2400 (I have an application where
> I need to stream short non-contiguous bursts, so I cannot afford to
> wait until it stabilizes for every burst).
> And by the way, should I also expect to see this behavior in the
> CBX/UBX daughterboards?
Analog hardware has its non-ideal behaviors, and at turn-on is one of
those times where it's more obviously non-ideal.
There are several things going on that can affect signal quality at
start of streaming:
o Enabling of various analog elements
o PLL instability --- are you tuning every time you stream a burst?
o DC offset correction -- it takes a while to reach equillibrium
o DSP filter discontinuities
You can either stream continuously, and use timestamps to decided which
parts of the stream to pay attention to, or you can schedule
your RX bursts a little bit ahead of when you need them, and use
timestamps to decide what to pay attention to.
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