Hi Ed. I'm rarely on in the evenings and mainly on Saturday and Sunday afternoons and on holidays...and on rare occasions as K5STB/P on Saturdays.
UR Questions... 1) Can you suggest a reference on HF propagation that may show distributions or histograms of fade depths, durations and bandwidths? No...I generally use the NVIS HAP charts from http://www.ips.gov.au/HF_Systems/7/1/1 Realtime fade depths, durations and bandwidths are going to change so much that you would probably have to be on-the-air at both ends of a path to determine this for any one band of frequencies. 2) For the examples of military equipment you gave, did they use voice bandwidths (~2.5 KHz) or were the bandwidths larger? Most has 2.7 KHz receiver bandpass filters or slighly less. CW filters were 400 Hz and AM filters were 6.x KHz. Most units used AME-USB with re-injected carrier so wht bandwidth was the same as SSB 3) With military communications I expect that voice quality and accuracy of the communication is essential. For ham weak signal applications where accuracy is not a life and death matter, can we gain any performance by trading codec data for FEC data? If voice quality at 2400 bps is considered acceptable for military applications, can we get better SNR performance with useable voice quality for ham applications at codec data rates less than 2400 bps with stronger FEC? You would think that voice quality and accuracy would be essential and in fact it is. However, the reason they sent from 1200 baud to 2400 baud for DV was just that and when signal levels were good enough, they used 4800 BPS. The robustness for the 2400 bps DV wasn't all that good...something more than a + 10 dB SNR was required. A more robust DV that would work with SNRs of 0 to -5 dB would be great...but then you could use 4800 bps DV at +10 SNRs. The qualitity of the AOR DV units is nice...very clear...I don't think that part needs much imporvement. However, they require such a high SNR that they can't be considered very robust. Walt/K5YFW -----Original Message----- From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] Sent: Wednesday, October 11, 2006 3:34 PM To: digitalradio@yahoogroups.com Subject: [digitalradio] Re: Digital Voice: Some thoughts after one week. --- In digitalradio@yahoogroups.com, "DuBose Walt Civ AETC CONS/LGCA" <[EMAIL PROTECTED]> wrote: > > I've heard DV using LCP-10 and a 16 tone modem as well as a 39 tone modem at 1200 bps...it sounds robotic at best. But that could have been just the systems used (ANDVT/Mil-STD-188-110) > > Walt/K5YFW Walt, Thanks for your very interesting and informative comments. I would be very interested in meeting you on the air for an extended conversation on the subject. We should be able to connect on 40M or 80M in the evenings. I often monitor 7295 +/-. I can also be reached on EchoLink. Some of the questions I have are: 1) Can you suggest a reference on HF propagation that may show distributions or histograms of fade depths, durations and bandwidths? 2) For the examples of military equipment you gave, did they use voice bandwidths (~2.5 KHz) or were the bandwidths larger? 3) With military communications I expect that voice quality and accuracy of the communication is essential. For ham weak signal applications where accuracy is not a life and death matter, can we gain any performance by trading codec data for FEC data? If voice quality at 2400 bps is considered acceptable for military applications, can we get better SNR performance with useable voice quality for ham applications at codec data rates less than 2400 bps with stronger FEC? Is there anyone reading this thread that could develop additional experimental modes for WinDRM? Ed WB6YTE Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) Yahoo! Groups Links Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/digitalradio/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/digitalradio/join (Yahoo! ID required) <*> To change settings via email: mailto:[EMAIL PROTECTED] mailto:[EMAIL PROTECTED] <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/