Hi David I am happy to hear, that 700 has no advantage over 700B. So, I will make experiments with 700B only.
I can increase the power easily, it is just a scaling factor, that I apply, when sending with codec2. My PA with a BLF188XR can run 500W over extended periods, it is water cooled. I will increase codec2 power to about 50 to 100 W, there is no danger. About the SNR-estimation: I just display the value that I get from calling float codec2snr; freedv_get_modem_stats(freedvRx,&codec2sync,&codec2snr); I display codec2snr in my sdr window. What is the typical range of numbers in this value? We will do low SNR experiments soon and report about our results. Thanks again Alfred On 31.08.2015 22:56, David Rowe wrote: > Hi Alfred, > > Thank you for your fine report. Some comments: > > Rx audio filtering isn't important for FreeDV as the demodulator has > it's own filters - one for each modem carrier in fact. > > 1/ Based on reports so far (and my tests) - I don't think 700 has any > advantage over 700B. We'll probably remove 700 from later releases, > it's included for compatibility for now. > > 2/ The initial frequency offset estimator for the cohpsk modem used in > 700(B) has a small initial lock range of +/-60Hz (FreeDV 1600 is +/- > 200Hz). Doesn't seem to be a problem in practice, once you are used to > it. Good to see it's locking up fast - I put a lot of work into it! > > 3/ 700(B) has been designed for a low crest factor (PAPR). You might be > able to drive the PA harder (if your PA doesn't get hot - pls be careful). > > 700B works down to around 0dB SNR (measured in 3000Hz), so perhaps there > is an issue in your SNR estimation code for strange waveforms like FreeDV. > > Can you pls tell me how well 700B worked in low SNR channels compared to > SSB? That is an important goal of FreeDV for 2015. > > Thanks, > > David > > ------------------------------------------------------------------------------ _______________________________________________ Freetel-codec2 mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freetel-codec2
