[time-nuts] DDS on AD9852

d0ct0r time at patoka.org
Sat Jan 17 05:02:18 UTC 2015




Hello,

I would like to ask some advise about the signal distortion I get from 
my DDS project.
The T-Bolt GPSDO is in use as a REF signal source (10Mhz) for AD9858 
DDS. This chip has two COS analog outputs which opposite to each other. 
I am using 20x reference multiplier in my project. And I am using Low 
Pass filter and RF amplifier connected to ONE of the COS output. The 
other output has no filter or op-amp on it. Attached is four files with 
OSC screen shots, where the signal which goes through the filter and 
amplifier somehow distorted. In contrary, the signal from another output 
(without filter and op-amp) has near perfect curve. I am using the same 
cable for connection to Oscilloscope.. And I set 5 Mhz output on DDS as 
an example. In this my project I am using Ten-Tec broadband pre-amp. The 
filter is standard Chebyshev Low Pass filter made by MINI-CIRCUITS. 
Model PLP-90 (81 Mhz).

Here is the link to Ten-Tec
http://www.tentec.com/products/Universal-Low%252dNoise-Broadband-DC-to-1-GHz-RF-Preamp-%252d-Model-1001.html


Is it normal to have that kind of distortions for the signal, or 
something wrong with design ?

-- 
WBW,

V.P.
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