Re: RF out with RF OFF: Clock feed through


EB4APL
 

Since we are fighting with a single frequency, probably the best filter solution would be a trap.  I just modeled the elliptical filter used in the DDS-60 using  AADE filter design program and the series "traps" resonance is not good for 180 MHz. Then I changed the capacitor values and the response seems to be much better in this respect. I think that I'll implement this mod to see what happens.

I'll try to attach the graphs, and if it doesn't work I'll upload them to the photos section.

73 de Ignacio, EB4APL


El 11/07/2017 a las 17:17, Nick Kennedy kennnick@... [PHSNA] escribió:
 
A filter with a steeper slop ought to help.  The transformer hasn't yet been shown to remove the clock signal.

Actually, the DDS-60 has more 180 MHz content than the AD9851 boards with outboard filtering. But individuals  may have done their filters differently, I suppose.

73,

Nick, WA5BDU


On Tue, Jul 11, 2017 at 8:31 AM, mendiola_loyola@... [PHSNA] <PHSNA@...> wrote:
 

Is the use of the transformer at the output the only solution to avoid the 180 mhz clock  feedthrough in the output ?


I understand that the DDS-60 has the same problem because it doesn't use a transformer at the output.

73.
Alfred
OA4AJP


Posted by: Nick Kennedy


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