[time-nuts] DDS on AD9852

paul swed paulswedb at gmail.com
Sat Jan 17 10:35:50 EST 2015


The DDS puts out perhaps a volt far to large for a preamp device. I suspect
like everyone else you are clipping. Just take a 2n3904 use it as a common
collector/buffer and bias the emitter for a clean cycle and see what level
you get.
Regrads
Paul
WB8TSL

On Sat, Jan 17, 2015 at 2:51 AM, Tom Miller <tmiller11147 at verizon.net>
wrote:

>
> ----- 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?
>
> Regards
>
>
>
>
>
>
>
>
>
>
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