Hi David, You are right, it was measurement error. With the help of Brady's GRC flowgraphs, I was able to set up a more reliable test. The chain was: gnuradio DBPSK modem on laptop -> Yaesu FT60 set on narrow deviation -> USRP B200 -> Gqrx The USRP has fine adjustable gain, between 0 and 70 dB. I was able to obtain error free copy at 18 dB above noise or 6 dB above (scratchy) analog FM. I am using a packet encoder so if 1 bit is lost the whole packet is dropped. The interesting thing is that sometimes the modem would decode at barely 10 dB above noise. It was critical to adjust audio levels so that the radio does not over deviate. Also, FM modulation does strange things to my phase, so I had to run a very tight FLL band edge loop to keep the constellation stable. I think there is still lots of room for improvement there. Also, I could not make the MSK modem decode after Gqrx demodulation, although if I use two analog radios it passes just fine. So I can't provide measurements for that modem. Hope this is useful,
Adrian (YO8RZZ) On 17 March 2016 18:50:37 GMT, David Rowe <da...@rowetel.com> wrote: >Hi Adrian, > >Getting the modem right can be really critical. It's good that we are >discovering this and talking about it in Ham and open source circles, >and getting high quality modem code out there. > >I learned about modems in the sat-com industry. As the satellites are >expensive, we would try to get our modems to within 0.25dB of theory. >Otherwise we were just wasting mega-$. > >It still puzzles me why something like DMR has deliberately chosen a >modem waveform (with less than Rs Hz spacing tones) that hobbles the >system by 6dB. The power being wasted is like throwing away 3/4 of >your >HT battery. > >Suspect of your 16dB loss is a measurement error or perhaps the FM >modem >is not set up right. I found simulating analog FM and getting >performance like the text books to be surprisingly difficult: > > http://www.rowetel.com/blog/?p=3799 > >Maybe you could first test your FM modem, see if you can get the C/No >input versus SNR out curve. > >Looking forward, FreeDV 2400A is competitive with SSB for weak signal >work today, and I think we can push down another 10dB over time. > >Cheers, > >David > >On 17/03/16 23:11, Adrian Musceac wrote: >> Hi Brady, David, >> >> Thank you very much for sharing the GRC flowgraphs. This will help me >> a lot setting up a similar test. Regarding the performance, I was >just >> surprised to see such a big difference between a modem which runs >> through analog FM and your new modem. I would have expected something >> in the range of 6-10 dB, not 16-20 dB. Maybe I need to calibrate my >> signal again. >> I enjoyed a lot reading about the experiment on your blog David. It >> seems like a new revolution for VHF/UHF weak signal work. >> >> 73, >> Adrian (YO8RZZ) >> >> On 3/17/16, Brady O'Brien <brady.obrien...@gmail.com> wrote: >>> Hey Adrian, >>> >>> The gnuradio-companion pipelines I used for the test are attached. >These >>> grc pipelines are only meant to get 16-bit 48k samples in and out of >the >>> HackRF and rtlsdr for testing. The meat of the FSK is done with the >C fsk >>> modem, used in freedv_rx, freedv_tx, fsk_mod, and fsk_demod. We are >also >>> running our FSK modem directly from SDR samples instead of through >FM >>> radios. We will be running 2400B over legacy FM radios, but don't >yet have >>> the same degree of test coverage. >>> >>> Thanks, >>> >>> Brady O'Brien >>> >>> On Wed, Mar 16, 2016 at 3:34 PM, Adrian Musceac <kanto...@gmail.com> >wrote: >>> >>>> Hi David, >>>> >>>> Is it possible to get our hands on the Gnuradio code? I've been >trying >>>> to optimize modems running at 1200 bits/second and the best I could >do >>>> was 100% copy at 8 dB above analog FM for DBPSK and 12 dB above for >>>> GMSK. Your modem seems to be 16-20 dB better than that! If I could >see >>>> the Gnuradio graph maybe I could figure out what I'm doing wrong. >>>> >>>> Thanks, >>>> Adrian >>>> >>>> On 3/16/16, Steve <coupaydevi...@gmail.com> wrote: >>>>> Ha, I wish it was through a radio! >>>>> >>>>> I'm trying to think what I have laying around here that might make >a >>>>> good >>>>> transmitter for it. >>>>> >>>>> On Wed, Mar 16, 2016 at 4:02 AM, glen english ><g...@cortexrf.com.au> >>>> wrote: >>>>> >>>>>> ah. good stuff. nice progress. >>>>>> >>>>>> >>>>>> On 16/03/2016 7:50 PM, Steve wrote: >>>>>> >>>>>> Just using the script: >>>>>> >>>>>> freedv_tx 2400A ve9qrp_10s.raw modem.raw >>>>>> >>>>>> Which produces a RAW audio file sampled at 48 kHz and importing >that >>>> into >>>>>> audacity. >>>>>> >>>>>> On Wed, Mar 16, 2016 at 3:46 AM, glen english ><g...@cortexrf.com.au> >>>>>> wrote: >>>>>> >>>>>>> Hi Steve >>>>>>> >>>>>>> Nice >>>>>>> >>>>>>> is that through a PA- if so, linear or linear in say 3dB >compression? >>>>>>> >>>>>>> >>>>>>> On 16/03/2016 7:42 PM, Steve wrote: >>>>>>> >>>>>>> Thought I'd upload a spectrum snapshot. You can't really see the >>>>>>> carriers >>>>>>> until you drop the number of samples to about 256, but this >shows how >>>>>>> wide >>>>>>> it is. >>>>>>> >>>>>>> I noticed that the freedv_tx was outputting +/- 1.0 signals and >a >>>> couple >>>>>>> of clips going on. Maybe need to knock it down to +/- .5 like >the old >>>>>>> FDM >>>>>>> modes. >>>>>>> >>>>>>> FYI >>>>>>> >>>>>>> Steve >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>> >------------------------------------------------------------------------------ >>>>>>> Transform Data into Opportunity. >>>>>>> Accelerate data analysis in your applications with >>>>>>> Intel Data Analytics Acceleration Library. >>>>>>> Click to learn >>>>>>> >more.http://pubads.g.doubleclick.net/gampad/clk?id=278785231&iu=/4140 >>>>>>> >>>>>>> >>>>>>> >>>>>>> _______________________________________________ >>>>>>> Freetel-codec2 mailing >>>>>>> listFreetel-codec2@lists.sourceforge.nethttps:// >>>> lists.sourceforge.net/lists/listinfo/freetel-codec2 >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>> >------------------------------------------------------------------------------ >>>>>>> Transform Data into Opportunity. >>>>>>> Accelerate data analysis in your applications with >>>>>>> Intel Data Analytics Acceleration Library. >>>>>>> Click to learn more. >>>>>>> http://pubads.g.doubleclick.net/gampad/clk?id=278785231&iu=/4140 >>>>>>> _______________________________________________ >>>>>>> Freetel-codec2 mailing list >>>>>>> Freetel-codec2@lists.sourceforge.net >>>>>>> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 >>>>>>> >>>>>>> >>>>>> >>>>>> >>>>>> >>>> >------------------------------------------------------------------------------ >>>>>> Transform Data into Opportunity. >>>>>> Accelerate data analysis in your applications with >>>>>> Intel Data Analytics Acceleration Library. >>>>>> Click to learn >>>>>> >more.http://pubads.g.doubleclick.net/gampad/clk?id=278785231&iu=/4140 >>>>>> >>>>>> >>>>>> >>>>>> _______________________________________________ >>>>>> Freetel-codec2 mailing >>>>>> listFreetel-codec2@lists.sourceforge.nethttps:// >>>> lists.sourceforge.net/lists/listinfo/freetel-codec2 >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>> >------------------------------------------------------------------------------ >>>>>> Transform Data into Opportunity. >>>>>> Accelerate data analysis in your applications with >>>>>> Intel Data Analytics Acceleration Library. >>>>>> Click to learn more. >>>>>> http://pubads.g.doubleclick.net/gampad/clk?id=278785231&iu=/4140 >>>>>> _______________________________________________ >>>>>> Freetel-codec2 mailing list >>>>>> Freetel-codec2@lists.sourceforge.net >>>>>> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 >>>>>> >>>>>> >>>>> >>>> >>>> >>>> >------------------------------------------------------------------------------ >>>> Transform Data into Opportunity. >>>> Accelerate data analysis in your applications with >>>> Intel Data Analytics Acceleration Library. >>>> Click to learn more. >>>> http://pubads.g.doubleclick.net/gampad/clk?id=278785231&iu=/4140 >>>> _______________________________________________ >>>> Freetel-codec2 mailing list >>>> Freetel-codec2@lists.sourceforge.net >>>> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 >>>> >>> >> >> >------------------------------------------------------------------------------ >> Transform Data into Opportunity. >> Accelerate data analysis in your applications with >> Intel Data Analytics Acceleration Library. >> Click to learn more. >> http://pubads.g.doubleclick.net/gampad/clk?id=278785231&iu=/4140 >> _______________________________________________ >> Freetel-codec2 mailing list >> Freetel-codec2@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 >> > >------------------------------------------------------------------------------ >Transform Data into Opportunity. >Accelerate data analysis in your applications with >Intel Data Analytics Acceleration Library. >Click to learn more. >http://pubads.g.doubleclick.net/gampad/clk?id=278785231&iu=/4140 >_______________________________________________ >Freetel-codec2 mailing list >Freetel-codec2@lists.sourceforge.net >https://lists.sourceforge.net/lists/listinfo/freetel-codec2 -- Sent from my Android device with K-9 Mail. Please excuse my brevity. ------------------------------------------------------------------------------ Transform Data into Opportunity. Accelerate data analysis in your applications with Intel Data Analytics Acceleration Library. Click to learn more. http://pubads.g.doubleclick.net/gampad/clk?id=278785231&iu=/4140 _______________________________________________ Freetel-codec2 mailing list Freetel-codec2@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freetel-codec2
