So I found the loopback script, tied the ends together with a multiply const block and was successful in modding and demodding that sinusoidal waveform. Added a UHD source and sink, success again. Then I split the process into two separate GRC files, a TX and a RX script. Everything works. I am extremely happy right now to see OFDM work. Thank you for the nudge in the right direction.
So the next question I have is why I have success with the hierarchal blocks in the loopback script but not so much with rx_ofdm or that custom loopback I posted? Even with a binary file source with the modulated signal, that rx script won't work. I wouldn't say too terribly important but it is interesting to learn how OFDM works. But for what I am working on, those hierarchical blocks will suffice. Thanks again. Jon On Thu, Mar 20, 2014 at 5:05 AM, Martin Braun <martin.br...@ettus.com>wrote: > A good way to test is to use the hier blocks for OFDM (you still need to > reduce amplitude), they will set up everything in a way that will work > for sure. See the loopback example in gr-digital/examples/ofdm. > > M > > On 03/19/2014 08:41 PM, Jonathan Fox wrote: > > Thanks for the responses. > > > > When I use the USRPs the UHD sink is placed after the OFDM Cyclic > > Prefixer, right after the Mutliply Const (50m). I haven't changed any > > settings because I remember reading in a few previous emails that the > > most common question people ask is "Did you change anything?" > > > > Sadly, the delay wasn't the case, at least for the loopback mode. > > > > I reduced the amplitude of the signal by an additional 0.02, so the > > multiply constant is at 0.03 as opposed to 0.05. It brought the clipping > > well within +1, -1. Before the signal clipped past -1 but never rose > > above +1. No effect but I am not ruling out that it wouldn't help. > > > > The video is interesting enough that I am going to continue watching > > after the first half, maybe I can figure out more from there. > > > > Jon > > > > > > On Wed, Mar 19, 2014 at 7:50 AM, Martin Braun <martin.br...@ettus.com > > <mailto:martin.br...@ettus.com>> wrote: > > > > On 03/19/2014 12:25 AM, Jonathan Fox wrote: > > > So I have the stock python scripts (tx_ofdm and rx_ofdm) located > > in the > > > gr-digital examples and put USRP sources and sinks in the > appropriate > > > spots. I left sampling alone (100K for TX, 3.2M for RX) and had the > > > TX/RX frequency at 500 MHz. The USRPs used are N210s with WBX > > > daughterboards. I tested the USRP used for TX out by outputting a > > signal > > > to another and looking at it on the GNU Radio spectrum analyzer. > Also, > > > this is through SMA cables and a 30 dB attenuator, no over the air > > > transmission. I placed file sinks after each block in the process; > > each > > > file is a binary file. After multiple runs I felt like something > > wasn't > > > working after looking at the binary files. > > > > Maybe you're probably screwing up your tx signal by clipping, > although I > > can't say for sure from your flow graphs (where exactly do you put > the > > UHD sink?) See > > > http://video.fosdem.org/2014/AW1125/Sunday/Tutorial_OFDM_Packet_Transceivers.webm > , > > starting around ~27 mins for an explanation, or search the mailing > list > > archive. > > > > Martin > > > > > > > > When I execute, only the file sinks placed after the Schmidl & Cox > > OFDM > > > Synchronizer freq_offset and detect have data in them, at least > their > > > files have some size to them, implying something has been written. > The > > > file sinks after FFT (or the header/payload demux) have no data, 0 > KB. > > > > > > When I discovered that the receive didn't work, I took the grc file > > > another user made back in October with both TX mod and RX demod in > the > > > same flowgraph to see if that would work (files attached). Again > same > > > issue, all the binary files after the FFT have no data so > something is > > > getting screwed up in my demod. > > > > > > Has any user on this list run into this issue before or can offer > some > > > insight to why the receiver is failing? > > > > > > Thank you, > > > > > > Jon > > > > > > Attached is the python script, grc file, and screen shot of the > TXRX > > > combo in GRC. > > > > > > > > > _______________________________________________ > > > Discuss-gnuradio mailing list > > > Discuss-gnuradio@gnu.org <mailto:Discuss-gnuradio@gnu.org> > > > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > > > > > > _______________________________________________ > > Discuss-gnuradio mailing list > > Discuss-gnuradio@gnu.org <mailto:Discuss-gnuradio@gnu.org> > > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >
_______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
