[Elecraft] K3 & ADAT ADT-200A by HB9CBU

[Philip Covington]

On Tue, Dec 2, 2008 at 8:05 AM, David Woolley (E.L)
<forums at david-woolley.me.uk> wrote:
> Philip Covington wrote:
>
>> problem of the phase noise of the LO.   Even QSD based SDRs which use
>> a DDS for the LO have worse phase noise (and spurs) than the crystal
>> oscillator LO in direct sampling receivers like the Perseus or QS1R.
>
> It seems to me that high speed A/D conversion is much more difficult to do
> accurately than high speed D/A conversion, so any degradation in converting
> the LO to analogue is going to be more than compensated for by that in
> converting a wideband signal to digital.
>
> --
> David Woolley

It may seem that way to you, but in real life it turns out the the DDS
generates spurs due to only approximating a sin function, clock
leakage, number of bits, etc...  There is not the same issue in the
NCO generated LO in the FPGA in direct sampling receivers such as
Perseus and QS1R.

-- 
Phil Covington
Software Radio Laboratory LLC
Columbus, Ohio
http://www.srl-llc.com