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

Jorge Miguel jmiggal at gmail.com
Sat Nov 13 04:10:35 EST 2010


Now I wonder how it is possible that I can send a perfect sine wave at
frequencies of KHz (20KHz, 50KHz, 100KHz) to my oscilloscope from the basic
TX. Shouldn´t it be filtered by the transformers?


On 12 November 2010 17:34, Matt Ettus <matt at ettus.com> wrote:

> 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.
> Matt
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