Re: DDS spectral "purity" ?

Jaques Anthony
 


Hi Nick,
     Interestingly (I think) although I see the message header for your current posts, I do not see any content! I can see it in the e-mail version that I get though.
     This business of noise when changing frequency cam to light when I used a MK2 type module in an 80mtr receiver (the MKARS80). During tuning only with the rx at full gain (no aerial) there was a considerable increase in background noise. Looking at the output on a spectrum analyser showed a whole load of rubbish on the DDS output a few dB above its normal noise level when tuning.  I went back to an analogue VFO!
     But I still have the extracted DDS module so yesterday I tried to have another look. Unfortunately I no longer have access to the spectrum analyser. Instead I now have a Cushman CE15 "Spectrum monitor" This is similar to an analyser, but with limitations, and I can not see the effect on it.
     So was the effect real? I think so but I can not now prove it.
     But yes, it would not be present in single frequency mode.
                                                          Tony (G3PTD)

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