# 8-bit samples on USRP2 at 33.333Msps **URL:** \ **Category:** GNU Radio\ **Created:** [November 10, 2011, 4:09am UTC](https://www.ruby-forum.com/t/8-bit-samples-on-usrp2-at-33-333msps/213729 "2011-11-10T04:09:18Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![dubstep](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/cdc98d/32.png) [@dubstep](https://www.ruby-forum.com/u/dubstep)\ **Post date:** [November 10, 2011, 4:09am UTC](https://www.ruby-forum.com/t/8-bit-samples-on-usrp2-at-33-333msps/213729/1 "2011-11-10T04:09:18Z")
Just did a quick test of 8-bit samples on a USRP2, on one of my 6-core AMD machines. I can get to 33Msps with a fairly simple SOURCE–\>MULT–\>FFT\_SINK flow-graph, but anything more complicated causes overruns. If I try 50Msps, I get near-continuous overruns. This is on an AMD Phenom II X6-1055 – the cores run at 2.8GHz, and I have 4GB of 1333MHz memory. It’s a fairly-wimpy machine as multi-core DSP monsters go, but I thought I’d give it a try. 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. – Marcus L. Principal Investigator Shirleys Bay Radio Astronomy Consortium > **[Live Draw HK Tercepat | Result HK | HK Pools | Live HK | HK Prize Hari Ini](https://www.sbrac.org/)** > > Temukan live draw hk tercepat melalui halaman hk pools yang resmi dan dapatkan result hk prize melalui live hk secara langsung di situs kami. ---
**Author:** ![Marcus\_DSLeech](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/74df32/32.png) [@Marcus\_DSLeech](https://www.ruby-forum.com/u/Marcus_DSLeech)\ **Post date:** [November 10, 2011, 4:37am UTC](https://www.ruby-forum.com/t/8-bit-samples-on-usrp2-at-33-333msps/213729/2 "2011-11-10T04:37:38Z")
On 11/09/2011 07:07 PM, Marcus D. Leech wrote: > It’s a fairly-wimpy machine as multi-core DSP monsters go, but I thought > I’d give it a try. My AMD Athlon™ II X4 620 Processor does jyst fine with 50Msps FFT plotter. Just sayin 🙂 > 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 ---
**Author:** ![Marcus\_DSLeech](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/74df32/32.png) [@Marcus\_DSLeech](https://www.ruby-forum.com/u/Marcus_DSLeech)\ **Post date:** [November 10, 2011, 5:25am UTC](https://www.ruby-forum.com/t/8-bit-samples-on-usrp2-at-33-333msps/213729/3 "2011-11-10T05:25:03Z")
> > 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). Its a full complex scaler multiplier in the FPGA. You can pick any integer. Basically extract any of the bits you want. -Josh ---
**Author:** ![Marcus\_DSLeech](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/74df32/32.png) [@Marcus\_DSLeech](https://www.ruby-forum.com/u/Marcus_DSLeech)\ **Post date:** [November 10, 2011, 5:21am UTC](https://www.ruby-forum.com/t/8-bit-samples-on-usrp2-at-33-333msps/213729/4 "2011-11-10T05:21:56Z")
> My AMD Athlon™ 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 L. Principal Investigator Shirleys Bay Radio Astronomy Consortium > **[Live Draw HK Tercepat | Result HK | HK Pools | Live HK | HK Prize Hari Ini](https://www.sbrac.org)** > > Temukan live draw hk tercepat melalui halaman hk pools yang resmi dan dapatkan result hk prize melalui live hk secara langsung di situs kami.