Hi, I think a 3 to 6 dB backoff from the saturation power level of the PA is good choice for standard ham radio setups. This will help to keep the spectrum narrow and to avoid too much ACI. Even a 3 dB (inside-band IM free) compression seems allowed w/o degradation of transmission performance. Ill be on the road the next days, but afterwards Ill continue with some tests. BTW Alfred, HB9EPU and I are using linearized amps by means of adaptive pre-distortion so that we never paid too much attention that item, hi.
73, Helmut -----Ursprüngliche Nachricht----- Von: David Rowe [mailto:[email protected]] Gesendet: Mittwoch, 16. September 2015 01:57 An: [email protected] Betreff: Re: [Freetel-codec2] received SNRs Thank you Helmut, nice to have independent verification of the SNR estimation algorithm in the cohpsk modem. The MDS results are also quite exciting! Would it be possible please to test the effect of FreeDV 700B SNR, when the transmitter power amplifier is driven harder? On my simple tests here, I couldn't drive my IC7200 hard enough to cause any problems, so I am wondering where the limit is for 700B. For example if the peak/average ratio of the tx signal is 4 or 6dB, what is the SNR degradation as measured by FreeDV 700B? Thanks, David On 15/09/15 22:59, Helmut wrote: > Hi David, > > here the report of some tests this afternoon (sorry, screenshots can't be > packed more w/o heavy quality reduction). Moreover I'm not sure whether the > SNR on the FreeDV display is calibrated in dB. > First I checked the 'mean discernible signal' of mode 700B offering > reasonable readability: SNR -1 (dB?), signal in SSB channel -130 dBm, > visiable in the noise on the panadapter. I very impressive result!!! > Then I increased signal up to -123 dBm, + 7 (dB?) on freeDv display, > comfortable readability. In a further step I raised TX PEP power by 6 dB. My > calibrated S-Meter followed, while SNR display shows 5 (dB?) more. The > proven accuracy of the HPSDR S-Meter is +/- 0.5 dB. I think that's a good > compliance with the SNR show on the freeDV window. > > David, I hope this quick test helps a bit. > > 73, Helmut > > > > ---------------------------------------------------------------------------- -- > > > > _______________________________________________ > 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 ------------------------------------------------------------------------------ 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
