Re: [Discuss-gnuradio] Viewing square wave in usrp_oscope

[address@hidden]

I have been able to view square waves down to 1 KHz with the usrp_oscope. 
I do not use a daughterboard and I turned off the automatic DC offset.  I
input the signal into pins 62 and 60 of connector J666, of the USRP, with
the use of appropriate coupling capacitor.  I disabled the automatic DC
offset by adding the following code:

   self.u = usrp.source_c()                    # usrp is data source
   self.u.set_dc_offset_cl_enable(0x0, 0xf)    # Turn off auto dc offset

I turned off the DC offset to get ride of a drop in the square wave.  The
DC offset algorithm tries to remove what it considers DC signal and that
includes slow varying signals in the KHz range.

Original Message:
-----------------
From: sudhindra aithal kota address@hidden
Date: Fri, 18 Nov 2005 03:21:09 +0000 (GMT)
To: address@hidden, address@hidden
Subject: Re: [Discuss-gnuradio] Viewing square wave in usrp_oscope


Hi,
 Sorry for the previous mail. Totally out of context.

I gave a square wave input direct from a signal
generator and the behaviour of usrp_oscope was the
same as I had explained before. I increased the
frequency to way above 100KHz. Is there any other
option to be given?

Regards
Sudhindra


> Hi,
>  Is it possible to view a square wave using
> usrp_oscope.py? I have a circuit which produces a
> square wave that I want to view.

Yes.

>  I know usrp_oscope is not a general purpose
> oscilloscope. We eventually want to manipulate the
> signal coming from the circuit for our purposes. So
we
> wanted to know if it is represented properly.
>  The square wave had spikes in it. It appeared more
> like a capacitor charging and discharging. And at
high
> frequencies, it resembles a sine wave. The signal
> coming from the circuit has a frequency of 41 KHz. 

If you are using the Basic Rx daughterboard as your
input, the RF
transformer on it acts as a high pass filter.  
Try using an input signal > 100kHz.  A megahetz would
be even better.

>  Has anyone tried working with a square wave before
> and faced this problem? Please let me know how to
> correct this. Thanks

The Basic USRP has a 50 Ohm input impedance.  
Will your circuit drive 50 ohms?

Eric



                
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