Adding a DC offset to the output of a LFTX

I’m trying to add a DC offset to the output of my LFTX driven from a
USRP 1.
Is this possible progromatically? I edited my GRC block diagram to
include
adding a constant value to my complex stream, before inputting into the
USRP
sink block. I have a scope output at the same point, which shows adding
a
constant value to the signal, but the output of the USRP doesn’t match.
What
am I missing? I’ve tried adding both a constant real value, and a
complex
constant with equal parts I and Q - neither work.
Thanks.
-William

On 08/31/2010 07:50 AM, William C. wrote:

I’m trying to add a DC offset to the output of my LFTX driven from a
USRP 1. Is this possible progromatically? I edited my GRC block diagram
to include adding a constant value to my complex stream, before
inputting into the USRP sink block. I have a scope output at the same
point, which shows adding a constant value to the signal, but the output
of the USRP doesn’t match. What am I missing? I’ve tried adding both a
constant real value, and a complex constant with equal parts I and Q -
neither work.
Thanks.
-William

If you have a non-zero frequency set on the USRP then your DC offset
will be mixed to that frequency. If you really want DC offset then you
can not use the DUC, or you can use the registers in the AD9862 to add
DC offset after the upconversion. The registers will only give you a
limited range, however.

Matt

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