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

Matt Ettus matt at ettus.com
Mon Nov 15 00:05:59 EST 2010



The attenuation is a function of frequency.  If you send a sine wave, it 
is only one frequency, so it is just attenuated.  A square wave is 
composed of many frequencies, each attenuated a different amount, thus 
causing distortion.

The BasicRX and BasicTX are not designed to be used below 1 MHz.  I've 
said this several times.

Matt


On 11/13/2010 01:10 AM, Jorge Miguel wrote:
> Matt,
>
> 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?
>
> Regards,
> Jorge
>
> On 12 November 2010 17:34, Matt Ettus <matt at ettus.com
> <mailto: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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