On 5/3/19 at 1:58 PM, [email protected] (Bill Somerville) wrote:
your conclusions are all correct. We are currently fine tuning
the FT4 transmission start time so that the decoder gets a
reasonably even chance of decoding signals across the allowable
DT tolerance of ± 0.5 S without losing sensitivity. We can't
quite make it perfect across that range whilst still allowing
the user reasonable thinking time before the next transmission
period. FT4 has a shorter transmission time, shorter dead time
between periods, and shorter periods than FT8 so it should not
be surprising that clock accuracy requirements are stricter as
well. This really only matters for MS Windows users who have
not bothered to install a third-party NTP service, have no
suitable Internet connection, or GPS signal. For those that
rely on manual time setting or think Windows can do the job
well enough, now is the time to think again.
This issue may be important on other operating systems as well
as Windows.
When I'm in New Hampshire, I run FT8 using my cell phone for
internet connectivity and NTP access. I find that if I have left
the house for several hours and return, unless I reconnect to
the cell phone/Internet, my Macintosh's clock is off by enough
to impact decoding. I have trained myself to look at the delta
time column when I am getting decodes to make sure that my clock
is at least reasonably (< 0.5 seconds) synched with the others
on the band. When I get no decodes, but have signals on the
waterfall, the clock is the first place I look to solve the problem.
73 Bill AE6JV
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