... have just been released. I've added a "News" section to freedv.org with brief notes on the changes.
Thanks Richard for pushing these releases out there! - David On 25/09/15 04:44, David Rowe wrote: > It's an challenging area to play in, I worked out the theoretical limits > for DV here: > > http://www.rowetel.com/blog/?p=4053 > > > On 24/09/15 11:02, Bruce Perens wrote: >> I was thinking, for my Pacificon talk on 700B next month, of doing a >> take-off on the QST column "The World Above 50 MHz" called "The World >> Below 0 dB S/N". >> >> On Wed, Sep 23, 2015 at 5:49 PM, Matthew Cook <[email protected] >> <mailto:[email protected]>> wrote: >> >> David, >> >> Why can I see a discussion paper or magazine article entitled "do >> you know your Eb/No?" *grin*. >> >> 73 >> >> Matthew >> VK5ZM >> >> On 24 September 2015 at 05:46, David Rowe <[email protected] >> <mailto:[email protected]>> wrote: >> >> Nice work on the power measurement Helmut :-) >> >> I wanted to say a little about 0dB SNR and below operation. In >> the attached plot, the lower three curves show the performance >> of modems in AWGN channel - a channel that just has additive >> noise (like a very slow fading HF channel or VHF). >> >> These curves show how much energy/bit (Eb/No) we need for a >> certain Bit Error Rate (BER). >> >> The Blue curve just above the Red (ideal QPSK) perf is our modem >> in a AWGN channel. Time for some math: >> >> The energy/bit Eb = power/bit rate = S/Rb >> The total noise the demod sees is No (noise power in 1Hz) >> multiplied by the bandwidth B, N=NoB >> >> Re-arranging a bit we get: >> >> SNR = S/N = EbRb/NoB >> >> or in dB: >> >> SNR(db) = Eb/No(dB) + 10log10(Rb/B) >> >> Now Rb = 700, B = 3000 Hz (for SNR in a 3000Hz bandwidth) so we get: >> >> SNR = Eb/No - 6.3 >> >> Now, say we need a BER of 2% or 0.02 for speech, the lower blue >> curve says we need an Eb/No = 4dB, so we get: >> >> SNR = 4 - 6.3 = -2.3dB >> >> So if the modem is working down to "just" 0dB we are about 2dB >> worse than theoretical. This is due to the extra bandwidth >> taken by the pilot symbols (which translates to 1.5dB) and some >> implementation loss in the sync algorithms, and non linearities >> in the system. >> >> I thought it worth explaining this a little more. These skills >> will be just as important to Hams of the 21st century as Ohms >> law was in the 20th. >> >> Cheers, >> >> David >> >> >> >> >> >> On 23/09/15 18:04, Helmut wrote: >> >> Hi Glen, >> >> Very difficult question, hi! I left the commercial arena >> more than 12 years >> ago, so that have to use my old mixed surplus test >> equipment, certainly not >> competitive with today's requirements, but good enough for >> ham radio. >> The old R&S RMS-Powermeter with a tru-sensor provides a >> nominal accuracy of >> +/- 5 %. A PEP- module for this RMS meter offers similar >> accuracy for >> sinusoidal waveforms. From time to time I check the R&S >> meter with my (old) >> HP 435A and a reference circuit. >> The most accurate test equipment is finally my HPSDR setup. >> The feedback >> loop for the pre-distortion delivers an exact and well >> defined portion of >> the TX power to the RX input in real-time. As the ADC is >> driven to full >> scale or in minimum 15 dB below the failure is within +/- >> 0.3 dB for average >> or PEP indication (total dynamic range > 120 dB). >> For the exciting tests with Alfred, HB9EPU, to get a feeling >> how capable >> freeDV at small SNRs is, I always watch the displayed >> spectrum of the >> incoming signal. The FFT bin width is 2,93 Hz, that means >> that a signal is >> still visible, but no longer audible after processing in the >> phones. >> Therefore it was amazing, that freeDV seems to produce >> reasonable >> readability still with SNR =0 dB. >> >> 73, Helmut >> >> p.s. No experience with AD8362. Boonton (Wireless Telecom >> Group) offers a >> nice USB Peak Power Sensor. >> >> >> >> >> -----Ursprüngliche Nachricht----- >> Von: glen english [mailto:[email protected] >> <mailto:[email protected]>] >> Gesendet: Mittwoch, 23. September 2015 01:26 >> An: [email protected] >> <mailto:[email protected]> >> Betreff: Re: [Freetel-codec2] Tuning Aid 700B mode >> >> Helmut >> How well does your power meter respond to high peak to >> average signals, >> IE faithfully measuring peak and PEP ? I've been involved in >> this with >> DRM and DVB. >> >> something to watch, anyway. >> Maybe use a TRUPWR (R) device like the AD8362 to measure it. >> >> 73 >> >> >> On 23/09/2015 5:58 AM, wully wrote: >> >> Hi all >> >> Helmut, dc6ny, and I have done some more tests >> yesterday. The band >> starts opening again (wonderful: we always want to test >> 700B). >> As stated earlier, we never had any problem with the >> 700B-tuning: cohpsk >> locks quicker than the fdmdv, at least, this is the >> impression we get >> from our experiences. Yesterday, I started to reduce my >> power (measured >> by an LP-100A just before the antenna coupler) when >> txing in 700B. >> Helmut detected the signal and I reported about my power >> seting: Full >> drive started with 58Watts peak. Then I reduced the >> power to 100mW peak >> (reading the quickly changing "average" of LP-100A). >> This was the last >> setting, that I could read on the LP-100A, my relative >> powerseting was >> at 7 out of 256. Then I reduced to 6, then to 5, to 4, >> to 3, to 2. After >> this experiment, Helmut reported, that he could fully >> decode the signal >> at 6, but at 5 only about 50% and lower no decoding >> anymore. We >> estimated, that setting 6 was about 50 mWatt. >> >> >> >> >> ---------------------------------------------------------------------------- >> -- >> _______________________________________________ >> Freetel-codec2 mailing list >> [email protected] >> <mailto:[email protected]> >> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 >> >> >> >> ------------------------------------------------------------------------------ >> Monitor Your Dynamic Infrastructure at Any Scale With Datadog! >> Get real-time metrics from all of your servers, apps and tools >> in one place. >> SourceForge users - Click here to start your Free Trial of >> Datadog now! >> http://pubads.g.doubleclick.net/gampad/clk?id=241902991&iu=/4140 >> _______________________________________________ >> Freetel-codec2 mailing list >> [email protected] >> <mailto:[email protected]> >> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 >> >> >> >> ------------------------------------------------------------------------------ >> Monitor Your Dynamic Infrastructure at Any Scale With Datadog! >> Get real-time metrics from all of your servers, apps and tools >> in one place. >> SourceForge users - Click here to start your Free Trial of >> Datadog now! >> http://pubads.g.doubleclick.net/gampad/clk?id=241902991&iu=/4140 >> _______________________________________________ >> Freetel-codec2 mailing list >> [email protected] >> <mailto:[email protected]> >> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 >> >> >> >> >> ------------------------------------------------------------------------------ >> Monitor Your Dynamic Infrastructure at Any Scale With Datadog! >> Get real-time metrics from all of your servers, apps and tools >> in one place. >> SourceForge users - Click here to start your Free Trial of Datadog now! >> http://pubads.g.doubleclick.net/gampad/clk?id=241902991&iu=/4140 >> _______________________________________________ >> Freetel-codec2 mailing list >> [email protected] >> <mailto:[email protected]> >> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 >> >> >> >> >> ------------------------------------------------------------------------------ >> Monitor Your Dynamic Infrastructure at Any Scale With Datadog! >> Get real-time metrics from all of your servers, apps and tools >> in one place. >> SourceForge users - Click here to start your Free Trial of Datadog now! >> http://pubads.g.doubleclick.net/gampad/clk?id=241902991&iu=/4140 >> >> >> >> _______________________________________________ >> Freetel-codec2 mailing list >> [email protected] >> https://lists.sourceforge.net/lists/listinfo/freetel-codec2 >> > > ------------------------------------------------------------------------------ > _______________________________________________ > Freetel-codec2 mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > ------------------------------------------------------------------------------ _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
