Re: [digitalradio] New digital mode proposal for CW transceivers

[John B. Stephensen]

The problem with NVIS is that there are a lot of paths over which the transmitted signal can reach the receiver. When DRM was tested, they measured a 7 ms delay spread in an equatorial region and I've seen reports published on the Internet showing up to 13 ms. In near-polar regions, there is the additional problem that the doppler spread increases with ionospheric disturance and signals can be up to 39 Hz wide. In the worst case, the coherance bandwidth would then be about 75 Hz and the coherence time 25 ms. In this case, the ionospere is less stable than the transceiver.   Non-coherent detection may work best under both of these conditions. An FSK mode with lots of error correction would seem to be the most robust.     73,   John KD6OZH   ----- Original Message ----- From: Vojtech Bubnik To: digitalradio@yahoogroups.com Sent: Wednesday, November 01, 2006 09:10 UTC Subject: [digitalradio] New digital mode proposal for CW transceivers Hi gang. I am thinking of learning my SW+40 to talk digitally. I know of only two digital modes that may be exercised on this TRX without any hardware modification: morse and feld hell. The third possibility would be RTTY, but it would need to modify the TRX slightly. Although it may be done on SW+, the VFO pulling will be more dificult on direct conversion rigs, where the frequency shift is dependent on the frequency. The most used digital mode is still morse. The problem with computer decoded morse is that it is usually asynchronous and speed varies. Computers have great dificulty to decode morse signal under bad conditions. I know there have been some synchronous CW experiments, but the SCW mode was not widely accepted, mostly because PSK decoder may decode -3dB weaker signal. But how about modifying PSK31 software modem to send CW modulated signal? As far as my DSP knowledge goes it will be about 3dB worse than PSK31, but the signal will be wider than of PSK31. Never mind, it will be intended for QRP operation. PSK31 symbol speed is too fast for NVIS. PSK31 is hurt baddly by polar flutter. The new CW modulated mode will probably be not too much affected by polar flutter. Am I right? The speed of BPSK31 is about 40WPM. It makes sense to go down to 16 symbols per second to make the mode better for NVIS and still be usable. Or use the same symbol speed 31 and add simple FEC, for example from QPSK31, 2dB will be gained. How about that? Does it make sense to create another mode? 73, Vojtech OK1IAK __._,_.___ 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) SPONSORED LINKS Ham radio Ham radio antenna Ham radio store Digital voice Digital voice recorder mp3 Your email settings: Individual Email|Traditional Change settings via the Web (Yahoo! ID required) Change settings via email: Switch delivery to Daily Digest | Switch to Fully Featured Visit Your Group | Yahoo! Groups Terms of Use | Unsubscribe __,_._,___