[time-nuts] XOR frequency doubler question 5/10 Mhz

Charles Steinmetz csteinmetz at yandex.com
Fri Feb 20 17:52:42 EST 2015


Chuck wrote:

>To make decent use of this technique, I believe that you would have
>to install 20 to 30dB of 5MHz rejection, and a 10MHz low pass filter
>in the output circuitry....     *   *   *
>The 5MHz rejection filter is necessary to prevent phase anomalies
>from appearing due to the beating of the doubled 5MHz fundamental
>with the XOR gate created 10MHz signal.

If you start with 5MHz down 10dB in the output, and apply 30dB of 
filtering, you end up with 5MHz down 40dB.  That is nowhere near 
enough to avoid anomalies in stability plots.  You need the 5MHz 
component in the output closer to -80dBc than to -40dBc to get the 
anomalies down toward the noise floor.  That is a massive amount of 
filtering very close to the desired 10MHz output, and is why it is 
important to start with 5MHz below -40dBc straight from the doubler 
(no filtering).

Best regards,

Charles





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