Re: Thanks and DDS filter query


Hi David,

On the DDS filters...

The biggest issue is that the filter on the DDS module, regardless of whether a 9850 or a 9851 DDS is being used, is designed for a roll off at about 70 MHz. While this might be OK for a 9851, it is much too high for a 9850. That filter should roll off at a bit above 30 MHz.

Also, the L and C components used in the on-board filter are not of particularly high quality.

Finally, if you are using the "Type-2" DDS with the corresponding PHSNA or Experimenter boards, the circuit is designed to take the output from both of the available sinewave output pins and combine them with a transformer is a push-pull fashion, which helps to suppress even harmonics. The filter on the DDS module is applied to only one of the outputs, which would upset the symmetry.

You can certainly go "as is" for the time being and apply signal to the detector. It won't hurt anything. You probably just won't get quite as clean a signal as otherwise

The "Type-1" DDS and PHSNA board would be much more suitable if you wished not to remove the filter from the DDS. A filter of the appropriate roll off is included on the PHSNA board.

Jim, N5IB

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