[hpsdr] Hermes

[lstoskopf at cox.net]

I mentioned this before without any returned comments so here again as a 
warning/request for correction of my misunderstanding.

I have one of the QS1R boards which does not have a preamp.  Input 
voltage for the AD is basically Vdd plus the base breakdown voltage.  I 
popped the AD by turning an external pre-amp on before turning the QS1R 
on.  The preamp alone could not put out more voltage than the AD could 
stand IF IT WERE TURNED ON.  Phil C. left the preamp off so that the 
QS1R could be used in undersampling mode.  I would prefer to have the 
preamp chip in line to protect the expensive
AD, even if it does  reduce the dynamic range a bit.  Or a jumper 
block/solder link to put it in and out.  Comments welcome.  N0UU



> Looking over the information for Hermes in the wiki, a few thoughts.
>
> 1) Delete the LTC6400-20 preamp.  We can get differential drive to the 
> ADC using a transformer.  The 6400 reduces the dynamic range of the 
> system somewhat and complicates the design as well as raising the 
> cost.
>
> 2) Since off-board receive input filters are going to be needed 
> anyway, a suitable preamp and attenuator can be incorporated on that 
> board.  If Alexaires is the intended filter, perhaps it can be 
> modified to include a suitable preamp for the upper HF range.  Or use 
> of the RX1 in/out jacks on Alexaires can accommodate such a preamp.
>
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