Which non-English Morse characters are the most im. But as far as I know, the source code has not been releasted into the public domain yet by K1JT, so I cannot verify it now. My first impression from using the new JT9 mode is that the problem is much smaller there than for JT65, so maybe something like what I am discussing here has been done in the decoder software. There could potentially be other negative side effects on decoding also which I cannot foresee from the limited time I have used in trying to understand the algorithms. For this particular window the noise bandwidth goes up by a factor of 1.36 so sensitivity would suffer by 10log(1.36) or about 1.3 dB (ref: Harris, "On the use of Windows for Harmonic Analysis with the Discrete Fourier Transform," Proc. But as data is lost by the tapering, the downside is that the bin width increases. Software involved: HamRadio Deluxe & JT65-HF Hardware involved: FT-857D. I have operated this software and hardware for the past 4months in this configuration without a problem until now. This morning I ran across a weird issue with the JT65-HF software not decoding JT65 digital messages. This means that if the data had been multiplied by this taper, the dynamic range would have been in the order of 30 dB higher. Problem decoding JT65 messages in JT65-HF Software. 
There are many to chose from, but let's take a Hamming window as an example, with its first sidelobe 43 dB down.
When using the JT65-HF software, you'll need to adjust your thinking about the waterfall display. This could be remedied by using a smooth window function. Unlike WSJT which (if set to wide decode) only decodes the strongest message, W4CQZ's JT65-HF software will decode all messages in the 2000 Hz receive bandwidth 'window' (which is shown on the 'waterfall').
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