Glen, I'm no expert in detail, but I think this mentioned ETSI standard is a helpful paper for orientation and the Channel #6, path 4 profile describes the main challenges on HF coherently. Only the world above VHF is more comfortable, hi.
73, Helmut, DC6NY -----Ursprüngliche Nachricht----- Von: glen english [mailto:[email protected]] Gesendet: Dienstag, 31. Januar 2017 22:51 An: [email protected] Betreff: Re: [Freetel-codec2] FreeDV 700C early release When I read about frequency accuracy/ intolerance, it usually rings alarm bells on performance in those conditions To cope, most modems take a performance hit in return for required robustness. David, have a look at the ETSI spec for DRM http://www.etsi.org/deliver/etsi_es/201900_201999/201980/03.01.01_50/es_201980v030101m.pdf which includes the channel simulator data .... Annex B.1 modes A to D "Definition of channel profiles" Table B.1 Page 157, 158, suggest Channel # 6, path 4 You'll encounter like this channel profile local sunrise (not so much sunset), at 3.6 MHz, max distance 500km. Fast fading, high doppler, multipath and low SNR all characterise this comms mode. Uou'll be looking for someone in VK5. 800-1500 km paths do not encounter this problem (low doppler, low spread). What do you think Helmut ? I've heard that even DRM mode D has trouble under some conditions. glen VK1XX On 29/01/2017 11:06 PM, Helmut wrote: > Right, you hit the mark, Glen! > > 73, Helmut, DC6NY > > -----Ursprüngliche Nachricht----- > Von: glen english [mailto:[email protected]] > Gesendet: Sonntag, 29. Januar 2017 10:02 > An: [email protected] > Betreff: Re: [Freetel-codec2] FreeDV 700C early release > > The 64$ question is how well does it tolerate high doppler paths, being > vertical incidence and short ionospheric paths < 700km around local > sunrise and local sunset . > > On 29/01/2017 7:37 PM, Helmut wrote: >> Walter, >> >> many thanks for the clue, but I think we can exclude that possibility as we >> both using high precise and disciplined HPSDR stuff with accuracy of +/- >> 1Hz. While Alfred has implemented FreeDV via an API of his 'homebrew' SDR >> operation software I have access to the radio via VAC. As mode 700B works >> fine and 700C not, the problem seems hidden elsewhere. We'll find reason why. ------------------------------------------------------------------------------ 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
