Hi David, I don't believe that this mentioned noise plateau - approx. 32 dB below peak - of mode 700C inside the communication channel is caused by amps. Probably its caused by the modem itself.
I run my amps with high efficient linearization due to predistortion - currently a new advanced beta version - achieving 60 dB IMD! Moreover the inside channel noise plateau is also independent of the drive level or amp output. 73, Helmut, DC6NY -----Ursprüngliche Nachricht----- Von: David Rowe [mailto:[email protected]] Gesendet: Freitag, 3. Februar 2017 07:15 An: [email protected] Betreff: Re: [Freetel-codec2] FreeDV 700C early release Hi Gerhard, This actually dovetails neatly with Steve's PAPR work in the last post to this list. Unlike the 1600 and 800 modes, the COHPSK modulator used for 700C has some clipping on the output to improve the PAPR. In some PAs, this means you get get a higher average power output. In others, it may let the smoke out. This amplitude limiting is a form of non linearity and is probably the cause in the spectral regrowth at the edges of the spectrum that you are observing. Clipping can be disabled in the FreeDV GUI program Tool-Options menu. Cheers, David On 03/02/17 16:26, Gerhard Burian wrote: > Hi David, > > When I was testing the different modes with websdrs I recognized higher > sideband noise (shoulders) in 700C mode compared with 800XA and 1600 mode at > the same settings on my ANAN-100D. I am using narrow filtering on TX and > pure signal. So I don't have an explanation for that. > > Regards > Gerhard > > -----Ursprüngliche Nachricht----- > Von: David Rowe [mailto:[email protected]] > Gesendet: Dienstag, 31. Jänner 2017 11:40 > An: [email protected] > Betreff: Re: [Freetel-codec2] FreeDV 700C early release > > I been sending a few SSB/700C test signals of 800 - 1500 km paths on 40M > using a websdr to pick them up at the other end. In marginal conditions > with SSB down in the noise I'm getting sync and audio through on 700C. > Not sure if I have the same average tx power though. > > Also had a 700C QSO with a guy interstate. SSB very noisy but 6-8dB SNR on > 700C. Noise free but some issues with his audio and the modem loosing sync > every few seconds. > > Lot of frequency selective fading in both tests. > > Promising start.... > > - David > > ---------------------------------------------------------------------------- > -- > Check out the vibrant tech community on one of the world's most engaging > tech sites, SlashDot.org! http://sdm.link/slashdot > _______________________________________________ > Freetel-codec2 mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > > > ---------------------------------------------------------------------------- -- > Check out the vibrant tech community on one of the world's most > engaging tech sites, SlashDot.org! http://sdm.link/slashdot > _______________________________________________ > Freetel-codec2 mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/freetel-codec2 > ---------------------------------------------------------------------------- -- Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2 --- Diese E-Mail wurde von Avast Antivirus-Software auf Viren geprüft. https://www.avast.com/antivirus ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
