--- In [email protected], "D. J. Wang" <[EMAIL PROTECTED]> wrote: > >Hi Janne, >To avoid the spurs from DDS altogether it may be easier to use a >PLL/VCO instead. I was planning to build a 400-900 MHz PLL to drive the >SDR hardware but I don't have time to do it. Freq resolution of this >PLL doesn't need to be high since Winrad can cover a 48-192KHz window. >PLL step size can be in the range of 200KHz. It may be easier to build >than the DDS. Minicircuit Labs' POS-900W VCO will be a good choice for >this. I am not sure whether you can find a 7474 type of flipflop fast >enough to cover the freq range you need as it need to be able to divide >200MHz clock. > > 73 de DJ/NM3R
Hi DJ! So, you mean that DDS step accuracy is unnecessary because you can adjust the frequency within the bandwidth of Winrad screen? But, lets imagine that you want to adjust the frequency linearly all the time. I mean, you want to search HF FAX transmission at the 5-10MHz area, doesn't it just always jump in 200 kHz steps and then you have do a the adjustment in the Winrad window? If so, it sounds a bit difficult way. Well, if you can write proper software for it, then there is no problem, I know I cant :) Anyways, I think I'm gonna stick with the 'ordinary' DDS way - just two AD9954 to form I/Q, fed with pure high frequency signal. I think that will give pretty low spur levels, like mentioned earlier. Or do you think it's not clean enough? I really don't know since this is my first time wit DDS! 73 de Janne, OH1GTF
