Re: [Discuss-gnuradio] Gain Range error

[Matt Ettus]

On 01/16/2010 10:46 AM, Eric Schneider wrote:
> Just out of curiosity, was there a design decision made to not use the
> DAC PGAs to adjust Tx gain?


The issue is that changing the DAC PGA not only changes the differential 
amplitude (which is what you want), it also changes the DC bias point 
(i.e. the common-mode voltage).  If you change the DC bias point outside 
of a narrow range the upconverters don't work as well.

The only daughterboards that really make any use of the DAC PGA settings 
are the BasicTX and LFTX, which don't have this issue with common mode 
voltage.

Matt