[hpsdr] An high dynamic QSD front-end

[Philip Covington]

On 1/14/07, Robert McGwier <rwmcgwier at gmail.com> wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> Congratulations.  Very nice analysis,  very straightforward,  not
> requiring the machinery of Laplace transforms to understand the reasons
> which the "intuition impoverished mathematician" had to do to gain
> intuition.   If you study Leif Åsbrink's WSE hardware you will see the
> great lengths he went to do his "transient fix".   He was working very
> hard to supply the current from a suboptimal current source to overcome
> the transients problems with the four phase  capacitor
> pseudo-integrator.  He had a heuristic understanding of the need some
> time ago but did not go fully virtual ground, current mode with the
> necessary integrator to solve this in the utterly simple ISD Ahti has
> shown us.
>
> Thank you both for a serious elevation of this discussion.  It really is
> time to build hardware.  WARNING:  We definitely want to steer away from
> the FST switches.  FROM MEASUREMENT,  coupled with DDS issues,  they are
> the source of the increasing noise figure.  Marco's plots, as well as
> Phil C's and my measurements of various QSD's using them show this
> inescapable fact.  I think various pieces of analysis have incorrectly
> attributed the measurements but the switches are a major contributor.
> They solved an early problem and we can thank Gerald for finding this
> part and his very gracious publication in QEX and with the SDR-1000.
> But it is time to leave them behind FOREVER.
>
> 73's
> Bob
> N4HY

And we need a nice low noise LO to drive this circuit with.  Also
deciding whether to go with a AD9958/9 DDS or a PLL...

73 de Phil N8VB

 1168830890.0