On 12/14/2015 12:24 PM, Игорь Ч wrote:
> Hi Joe and all,
>
> In the JT65 protocol document there is statement: 'For the tests
> illustrated in Figure 4 with SNR less than about –29 dB, failure
> to synchronize is the cause of many failures to decode.'
>
> Quick question: why do not we transmit sync vector 3 dB higher
> than other tones? Some kind of the dynamic power control.
>
> 73 Igor UA3DJY
As far as I know your principal interest in JT65 is its use at HF.
Failures to decode JT65 signals at HF seldom have anything to do with
failure to synchronize. Indeed, at HF it would be better to have a
*smaller* (definitely NOT a larger) fraction of total Tx energy devoted
to the synchronization task.
The JT65 protocol document
http://physics.princeton.edu/pulsar/K1JT/JT65.pdf is mainly focused on
the EME path. Most amateurs doing EME run high power, with PAs running
at or near saturation. Nobody would choose to transmit their sync tones
at larger power than used for the message's information content.
-- 73, Joe, K1JT
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