Hi all,Several people have asked recently about relative sensitivities of the two-tone shorthand messages in JT65, which have been widely used for EME QSOs for nearly 20 years, and the "q3" decodes in Q65.
Facts relevant for EME on VHF bands are summarized in the attached plot. The results are based on realistic simulations of 100 transmissions of the message "RO" in mode JT65A, and 100 transmissions of the message "K1JT IV3NWV R-29" in Q65-60A, at each SNR. The simulated propagation conditions are those relevant for VHF EME, with 2 Hz (limb-to-limb) of Doppler spread.
The plot shows 50% decoding thresholds nearly identical for the two modes, despite the fact that much more information in conveyed by the Q65 protocol.
At SNRs 1-3 dB above the 50% threshold, JT65A shorthands produce slightly more single-transmission decodes than Q65-60A. However, at those signal strengths copy in both modes is already very good.
At SNRs below threshold Q65 is the clear winner, yielding 2.4 times more decodes at -33 dB and 5.3 times more at -34 dB.
The gradual slope of the Q65 curve, compared with the steeper slope for JT65, is a result of the gradual (and automatic) transition in Q65 between single-period decodes above threshold and average decodes below threshold.
-- 73, Joe, K1JT
JT65_RO_Q65_Rrpt.pdf
Description: Adobe PDF document
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