# Any way to sample/log the 50Mhz ISM signal in gnuradio with USRP2? **URL:** \ **Category:** GNU Radio\ **Created:** [July 12, 2014, 4:22am UTC](https://www.ruby-forum.com/t/any-way-to-sample-log-the-50mhz-ism-signal-in-gnuradio-with-usrp2/230916 "2014-07-12T04:22:01Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\ **Post date:** [July 12, 2014, 4:22am UTC](https://www.ruby-forum.com/t/any-way-to-sample-log-the-50mhz-ism-signal-in-gnuradio-with-usrp2/230916/1 "2014-07-12T04:22:01Z")
Hi guy, Thanks in advance. Currently I am implementing a project based on ofdm\_bentchmark example with USRP2. I remember that the sample rate of ADC of USRP 2 with RF2450 can be up to 100MS/s. That means we can use USRP2 to capture at most 50Mhz bandwidth signal. Initially, I plan to log the signal on my computer (_save as dat. format)_ and analyze it offline. Everything is fine when the sample rate(bandwidth) is set to 20MS/s in terminal. However, when we set the sample rate up to 50MS/s, nothing can be log in my computer. I guess there some software limitations in Gnuradio. My question is how to remove such limitation to achieve the 50MS/s sample rate. Any help will be greatly appreciated. Best, Kay ---
**Author:** ![Yingjie\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/f14d63/32.png) [@Yingjie\_C](https://www.ruby-forum.com/u/Yingjie_C)\ **Post date:** [July 12, 2014, 4:26am UTC](https://www.ruby-forum.com/t/any-way-to-sample-log-the-50mhz-ism-signal-in-gnuradio-with-usrp2/230916/2 "2014-07-12T04:26:47Z")
On 07/11/2014 10:20 PM, Yingjie C. wrote: > format)/ and analyze it offline. Everything is fine when the sample > > * * * > > Discuss-gnuradio mailing list > [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) > To achieve 50Msps, you’ll need to use 8-bit wire format, and set the > peak= parameter appropriately. There’s just not enough bits/second on a > 1GiGe link to support 50Msps with 16-bit, full-width samples. But you also need to consider the format you’re writing samples to disk in, and how much disk-write bandwidth you’ll require to support that. If you just use the same format (2 x 8bits) into the file, that’s 100Mbyte/second into the disk. That may or may not be supportable on your particular system. ---
**Author:** ![Yingjie\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/f14d63/32.png) [@Yingjie\_C](https://www.ruby-forum.com/u/Yingjie_C)\ **Post date:** [July 12, 2014, 1:49pm UTC](https://www.ruby-forum.com/t/any-way-to-sample-log-the-50mhz-ism-signal-in-gnuradio-with-usrp2/230916/3 "2014-07-12T13:49:19Z")
Just a side note: the 100MHz master sample clock rate of the USRP2 platform is _complex_ sampling, so internally the USRP2 processes 100MHz of bandwidth (not 50!), but that’s far too much to get it out via gigabit ethernet, and so it decimates these 100MHz down to the sampling rate you request as a user. ---
**Author:** ![Yingjie\_C](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/y/f14d63/32.png) [@Yingjie\_C](https://www.ruby-forum.com/u/Yingjie_C)\ **Post date:** [July 12, 2014, 10:17pm UTC](https://www.ruby-forum.com/t/any-way-to-sample-log-the-50mhz-ism-signal-in-gnuradio-with-usrp2/230916/4 "2014-07-12T22:17:46Z")
On 07/11/2014 11:04 PM, Yingjie C. wrote: > Thanks for your reply, Marcus. > > 8bits is enough for my case. But can you tell how to modify the adc > from 16bits to 8bits? I have no idea where to start it on gnuradio > example. _/What to mean by setting the peak/_?? what is the notation > of peak? The UHD source in GRC has a parameter for setting the wire format. [http://files.ettus.com/uhd\_docs/doxygen/html/structuhd\_1\_1stream\_\_args\_\_t.html](http://files.ettus.com/uhd_docs/doxygen/html/structuhd_1_1stream __args__ t.html) That’s for the raw UHD C++ interface, but see the notes about the “peak=” stream argument, which you can specify in the UHD source block in GRC.