Dear LF Group,
Congrats to G3LDO, VE1ZZ and VE1ZJ on their QSO - if nothing
else, it proves that the SNR in both directions across the pond can
be good enough to support 2 way communications in a reasonable
amount of time.
As regards GPS derrived clocks, etc, it seems to me that errors of
the order of 1us or so due to the GPS RX are always going to be
small compared to other uncertainties - for example, the distance
between the two stations can be determined quite accurately, but
ionospheric effects are bound to alter the effective length of the
path by much more than microseconds. Also, the group delay of the
average CW receiver filter must be at least a few milliseconds, and
this will be dependent on where the signal is in the passband, as
well as temperature/ageing effects. So the issue would seem to be
not so much how to get an accurate clock, but how to calibrate it
for a QSO over a particular path between stations using a specific
set of equipment.
Incidentally, the 2000 HP - sorry, Agilent catalogue says their
HP58503B GPS receiver will give time accurate to 110ns with
95% probability if I read the specifications correctly. The jitter on
the 1pps output is <750ps RMS. The 10MHz output is specified in
parts in 10^11 or 10^12 depending on the measurement period. It
is in a cute box like a bench digital multimeter. No doubt easy
mortgage terms are available....
Cheers, Jim Moritz
73 de M0BMU
|
