[hpsdr] Project proposal - Hermes

[Lyle Johnson]

Hello Kevin!

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.

3) The National LM4950TS makes a reasonable speaker amplifier. It is a 
linear device, so no switching noise.  The TPA2017 is interesting, but 
I'd be a little concerned about noise, including serious power supply 
decoupling since it shares the same analog domain as the LTC2208.

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This looks to be an exciting project!

73,

Lyle KK7P