If you're going for maximum reliability, it might be useful to use the widest possible subcarrier spacing to minimize sensitivity to Doppler combined with a guard interval long enough to compensate for NVIS multipath. This should give the widest possible coverage area. A carrier spacing of 8000/128 (62.5 Hz) and a guard interval of 1/2 (8 ms) has symbol rate of 41.7 baud and only 2 dB of power is lost in the guard interval.
73, John KD6OZH ----- Original Message ----- From: Rud Merriam To: digitalradio@yahoogroups.com Sent: Thursday, October 18, 2007 06:59 UTC Subject: [digitalradio] OFDM Proposal Here is a proposal for an OFDM protocol with a bandwidth of 493 Hz. The symbol rate is 29 Hz allowing 17 subcarriers. That provides 16 subsymbols and 1 pilot carrier. With PSK modulation and a 5 ms guard interval the effective symbol rate is 25.3 Hz which provides 405 bps. Any guesses on how well that would work? <g> Rud Merriam K5RUD ARES AEC Montgomery County, TX http://TheHamNetwork.net
