Re: [Discuss-gnuradio] Dropped data when changing frequency dynamically using an Ettus B200

[mleech]

No data are dropped, but there will *always* be a disturbance in the analog domain when you're changing the synthesizer frequency.  PLLs require a non-zero time to "lock", which means they converge to the correct frequency over some small time interval (a few msec, typically).  Along with this, the filters in the DDC will take <group-delay> time for the analog disturbance to propagate through the filter.

 

What underlying USRP device are you using?

 

 

On 2016-12-20 10:14, Tom Golden wrote:

Hi All,

 

I am connecting my flowgraph to a doppler prediction tool.  My block currently modifies a variable that is used to specify the center frequency of the USRP Source block.  The variable is updated every second.

 

When the variable updates, I see blank data (looks like all zeros) for a short blip when this occurs.  My QT FFT and Scope sinks flatline for a short period (subsecond).  Has anyone else seen this?

 

I've changed my flowgraph to leave the USRP Source alone and shift the frequency using a signal generator and multiply block.  I'm concerned about doing this for TX.  My concern is reduced performance because I'm not transmitting at the center frequency for the USRP Sink.  Is my concern unfounded?  Does anyone know if the same discontinuity for USRP Source is present for USRP Sink?

 

Thanks in advance,

-Tom

 

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