[USRP-users] DC biased output from LFTX DB
Marcus D. Leech
mleech at ripnet.com
Mon Jul 20 16:26:25 EDT 2015
On 07/12/2015 09:01 AM, Jeon via USRP-users wrote:
> I've built a such GNU Radio flow graph:
> I've connected USRP N210 with LFTX - SMA to alligator clip cable -
> oscilloscope to see what comes from the USRP. Nothing else is
> connected with them.
> And I've got the following waveform:
> Please ignore the blue readings.
> Yellow Max - Min says 800 mV and the amplitude will be 400 mV. Well,
> it's not that good, but it is okay and acceptable.
> But the offset doesn't seem to be right. I expect a square wave form
> swinging from -400 mV to 400 mV, but what I've actually got is, a
> square wave form swinging from -180 mV to 620 mV.
> Since, my application doesn't need a highly DC balanced signal, it's
> not a big deal but I am just curious about it.
> In addition, if I increase amplitude in the flow graph, a square wave
> form becomes very unstable. It fluctuates and goes up and down when it
> is supposed to show high voltage.
> And this problem makes me feel bad. I want to increase the amplitude
> as high as possible.
> Is my LFTX DB in some troubles?
Two immediate issues I see here:
You're running the USRP sink at 32ksps, which isn't a valid sample rate
I wouldn't expect to get more than about 2V P-P from the LFTX, since
it's largely just giving you (buffered) what the DAC can produce.
Not sure about the DC offset, but fix the sample-rate issues first, and
then see where you're at.
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