[hpsdr] Question re: RX attenuator

[John Marvin]

  I've been looking at the Mercury and Hermes schematics, along with the 
protocol document.  I've noticed that some software has a preamp 
enable/disable, while others have a -20db attenuator control.  Looking 
at the schematics, it appears that the preamp (which I believe is a 
LTC6400-20) is always enabled.  Mercury has a fixed 20 db attenuator 
that can be activated by a relay under control from the FPGA. Hermes has 
a 31 db step attenuator (DAT-31-SP) that can be controlled from the FPGA.

Looking at the protocol, it appears that there is only a preamp 
enable/disable bit.  Is that actually the control for the attenuator, or 
am I missing something? I assume this is only an on/off control due to 
the fact that Mercury only has a fixed 20 db attenuator.  Are there any 
plans to add support in the protocol (and PowerSDR, KK, cuSDR, etc.) for 
the Hermes attenuator, i.e. allow the attenuator to be set to anything 
from 0 to -31db?

Thanks,

John
AC0ZG