[USRP-users] DC biased output from LFTX DB

Jeon sjeon87+usrpusers at gmail.com
Sun Jul 12 09:01:00 EDT 2015


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?

Regards,
Jeon.
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