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## 9167Re: [wsjtgroup] JT65/JT4 - Max sync values + frequencies

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• Oct 1, 2012
Hi Bo,

OZ2M wrote:
> I wonder what is the highest possible "sync value" in JT65 and JT4 respectively? Even if I connect two PCs directly to each other I have not seen values above say 28. E.g. shouldn't it be 63 for JT65?

The sync value is a relative indicator only. It's not calibrated in any
particular units, and is necessarily linear. Its sole purpose is to
help establish whether a signal of the relevant mode is present at
particular time and frequency offsets DT and DF.

> Frequencies
> I have seen several values for the highest tone in JT65. For JT65C I have seen values from 685 Hz to 711 Hz. However, using the math from "The JT65 Communications Protocol, March 9, 2005" I cannot get anything else than ~700 Hz (JT65C) above the sync tone.
>
> Tone_N = Multiplier * (N+2) * 11025/4096, were
>
> Multiplier: ~A = 1, ~B = 2 and ~C = 4
> N: 0 to 63
>
> Thus for JT65C:
> Tone_0 = 4 * 2 * 11025 / 4096 = 21,533203125 Hz above sync
> Tone_63 = 4 * 65 * 11025 / 4096 = 699,8291015625 Hz above sync

Your numbers are correct. The figure 711 Hz is a good approximation for
the total occupied bandwidth of a JT65C signal, which is 66*4*11025/4096
= 710.5957... Hz (one tone spacing more than the figure 699.829... that
you calculated).

-- 73, Joe, K1JT
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