[Discuss-gnuradio] tx output level

[cswiger]

Just another stab - set_pga() seems to be screwy. With a
usrp_siggen.py looped back to usrp_oscope.py, not using
set_pga and amplitude 16e3 there's a signal peaking at 500.
However, use set_pga(0,n) (n=any value from 0 to 20)
and the signal drops to about 300.  Checking with

  print self.usrp._read_9862(0,16)

looks like we get 200 for any value of set_pga(0,n)

Using the private method self.usrp._write_9862(0,16,255) and
we get a peak 500 signal again.  While 200 should be the
max for 20db in .1db steps - it's stuck at 200. You can
POKE  (ha, showing my age there ;) values from 0 to 255 and
get different signal levels.

Also checked DAC A/B coarse gain and they look good at 192
for "Does not scale output current" and Rset on the schematic
is 4k. Per the AD9860 manual, "Iout of the Tx channels is a
function of the Rset resistor, the TxPGA setting, and the Coarse
Goan Control setting.

Also looks like broken information in the Register 16 docs, as
they only show 6 bits with max gain scaling as 63.

Bottom line, set_pga() seems to be broken on the tx side - but
it's stuck at max gain anyway.

--Chuck