At 09:33 AM 2/4/06, jgorman01 wrote: >1. I don't know why you say US hams cannot experiment on HF unless our >regs are changed. We currently have minimal bandwidth regulations. >Someone is certainly welcome to correct me, but I don't know of any HF >modem that tries to use 2 tones at 300 baud or higher. They all use >multiple tone modems and modulate individual pairs at a substantially >lower baud rate. Like 12 tone pairs, each at a rate of 60 baud which >give an equivalent rate of 720 baud, substantially over the 300 baud >regulation.
To help avoid the confusion that seems to creep in when talking about "bauds," for the example given, the state of each of the twelve binary sub-carriers represents one bit of the symbol being transmitted. That's one 12-bit symbol that changes state 60 times a second; the symbol rate is 60 symbols per second while the data rate is 720 bits per seconds. The rules put a limit on symbol rate that can be used not the bit rate that can be achieved. Inter-symbol interference due to delay spread from fading/multipath makes the restriction to a maximum symbol rate 300 baud a phantom limit at HF. Using DV as an example, the AOR modem sends a bit stream at a rate of 3200 bits per second using a symbol rate of 50 symbols per second; the various DRM modes send a comparable speeds with a maximum symbol rate is 37.5 symbols per seconds. Olivia (which is m-ary FSK and not multiple sub-carriers) includes a two tone configuration with symbol rates of 500 or 1000 symbols per second; the utility of that at HF is quite dubious. 73, Mike K1MK Michael Keane K1MK [EMAIL PROTECTED] 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/ <*> 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/
