NI USRP TX LO frequency tuning

[hesoyam]

I am facing the error while trinsmitting the IQ signal and stepping the output frequency dose any one have idea about that? Vi is attached. I know this is UHD error in GNU radio UUUUUU(The sampling rate with which the usrp is Transmint is gratter then the signal generated by the PC) but in LabVIEW i don't idea how to techel it.

Underflow: the Tx buffer was emptied before new data was provided.  Consider reducing the IQ rate, increasing the Write rate, or increasing the number of samples per Write.

Thank You

Junaid

[ErikL]

Some sggestions:

1. Visit the NI USRP Software Radio Discussion Forums for technical support.  This would be a good one for that forum managed by our tech support engineers.

2. Visit this link to download the latest NI USRP driver for LabVIEW.  We did some enhancements to improve Tx.

Looking at the VI, if you lock the LO you can only change the center frequency within the 40MHz bandiwdht of the device using the CORDIC.  So from a fiexed LO you have  +/- 20 MHz of bandwidth.  To change the center frequency across a broader range you need to stop the task, retune, and start the task again.

Erik

[hesoyam]

Hi Erik,

I am alrady using letest USRP driver 1.2. In retune process usrp thaks too much time. is there any sampling rate problem with tx sweep vi?

Thanks

[ErikL]

Its subtle but I see the problem.  It can be solved 2 ways.

The problem:  Remove the "Wait".  It's slowing the loop down.

If you want to send a burst of 10,000 points every second, you need to do the following:

1. use timed commands and set the start time at incrementing 1 second intervals.

2. use bursty transmission (set end of burst to true after each packet is sent)

Then each time you pass it data it will wait until the next second hits before the data is transmitted, then it will sleep until you've sent it data and the next specificied time is met.

(its important that you set the new time before sending data.  if you send data / call the VI before the new time is set it will tell you the time has already passed.)