[Elecraft] Re: K1 SSB?

[Trevor Jacobs]

Hi Wayne and all,

What about the new AD995X series with the 14 bit DAC? The inproved
resolution of the DAC should lower the spurs well below the 60 dB range.
I haven't played with them yet but they are worth looking into for this
type of application. What is the SFDR of the current VFO in the K1? I
haven't seen that information published. How far down do the spurs need
to be before they approach the kind of performance that we are seeing in
the K1 or K2 at the moment. The big advantage is the phase noise.
Looking at the output of a AD9850 on a spectrum analyzer, the phase
noise is almost non existant. Take care...

73's Trev KG6CYN
http://www.qsl.net/kg6cyn



> This will work, but are you also planning to include a phase-locked
loop to
> clean up the DDS's output? Using DDS as the injection oscillator by
itself will
> significantly degrade the performance of the K1's receiver. The
spurious-free
> dynamic range of any DDS with a 10-bit DAC, including the AD9834, will
only be
> in the 60 to 70 dB range at best. Large in-band signals will mix with
the spurs
> to produce numerous "ghost" images within the passband. This would be
especially
> noticeable during contests, but could be a problem anytime the band is
open or
> if you have strong nearby stations. For this reason, raw DDS VFOs are
only
> acceptible the simplest of equipment, or if the operator is willing to
accept
> the compromise.
>
> I wouldn't bring this up except that the K1's present performance is
> outstanding, and anyone contemplating making a DDS mod should be aware
of the limitations.