[USRP-users] Basic TX - Can DAC keep a voltage level ?

Matt Ettus matt at ettus.com
Fri Nov 12 11:34:01 EST 2010

On 11/12/2010 06:13 AM, Jorge Miguel wrote:
> Hi,
> I am trying to tx different signals with USRP2-basic Tx and Simulink.
> I can transmit a perfect sine wave.
> I can transmit a perfect pulsed carrier
> However, when trying to input the modulating pulse of the pulsed carrier
> I see on my scope spikes corresponding to the moment in which the pulse
> should go up and down (negative and positive respectively) but I cannot
> see a pulse shape. The duration of the pulse (time between spikes) and
> frequency as exactly the ones I set on my software.
> My thought is that the it can be possible that the DAC cannot drive
> enough current to my 50okms oscilloscope.
> Am I right? If not, what can be the reason?

The DAC has absolutely no problem holding a DC level.  You are using the 
BasicTX which has a transformer.  The transformer blocks DC.  If you 
want to output signals below 1 MHz you should use the LFTX instead, 
which does not have a transformer.

This goes for the RX side as well.  Anything under 1 MHz should use the 
LFRX instead of the BasicRX.


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