[time-nuts] DDS on AD9852

Tom Miller tmiller11147 at verizon.net
Sat Jan 17 02:51:55 EST 2015

----- Original Message ----- 
From: "d0ct0r" <time at patoka.org>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Saturday, January 17, 2015 12:02 AM
Subject: [time-nuts] DDS on AD9852

> 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.


You are overdriving the amplifier. What is the part number of Q1? It looks 
like a MAR-xx something.

The Tentek page does not have any good technical details on the amp that I 
could find. What info do you have?


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