[hpsdr] An high dynamic QSD front-end

[Ahti Aintila]

As requested by several people, I attach my latest schematic of the
180 degree ISD. This is a circuit that does not need the broadband
input transformer. The supply voltages suggested are not suitable for
the Odyssey project. You are free to modify as needed.

Another diagram with the input transformer will come with the next message.

73, Ahti OH2RZ


On 15/01/07, Philip Covington <p.covington at gmail.com> wrote:
> 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
>
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