Re: [Discuss-gnuradio] 8-bit samples on USRP2 at 33.333Msps

[Marcus D. Leech]

> My AMD Athlon(tm) II X4 620 Processor does jyst fine with 50Msps FFT
> plotter. Just sayin :-)
Hmmm, is the Athlon II generally better than the Phenom II (insns/clock? 
).  I suppose I should try it on my
  1090T as well, which is rather faster than the 1055T I tried it on 
tonight.  But that means lifting the
  1055T rack enclosure off of the 1090T, diving inside to pull the SD 
card of the USRP2, etc, etc.
  [My two USRP2 are mounted inside the 4U rack enclosures of their host 
computers].
  Perhaps tomorrow night :-)



> > People should be aware that since this uses the upper-half (as far as I
> > know) of the ADC, you'll need more gain to drive those
> >    8 bits.
> There is a configurable scale factor (see the stream args in the grc
> block). It defaults to a value that gives you the upper 8.
>
> -Josh
I noticed there was a "scalar=1024" option.  Is that just a multiplier 
that UHD applies on the host
  side for 8-bit samples, or does it affect the hardware (a barrel 
shifter or something).

The point I was trying to make was that if your analog samples don't 
"light up" more than the bottom few bits, grabbing the
  top bits (including sign) isn't going to give you much useful 
information in the samples (except the sign bit).  A couple of years
  ago when I was playing with 8-bit samples on the USRP1, I found I had 
to increase the gain of my analog componentry to get
  it to "light up" the top bits of the ADC, so that I had enough 
information that was "in range".










--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org