[time-nuts] Non-impedance matched antenna cables

phil fortime at bellsouth.net
Sat Jun 14 06:02:10 UTC 2008


I know you guys like to drill holes through hairs, but ....

As I follow the discussions on merits of 50/75 ohm cable, cable length 
changing with ambient temperature, tuning cable to a fraction of wavelength, 
power supply noise etc.

Does not the "weakest" link determine it's best accuracy?  If so, the 
receiver/electronics and internal programming seems to be the weakest link 
and all these small nano/pico second variables discussed seems moot, at 
least with unit in question.

If your receiver for example computes your location with a rather large 
error in lat/lon or altitude, that error I would think would be greater than 
the sum of all the "small" factors/errors being discussed. I have found, at 
least with the Thunderbolt receivers I have used, they are rather sloppy in 
it's location fix but even worse in it's altitude fix.

As I understand it, each foot of distance is a little over a nanosecond in 
delay so would not position/altitude accuracy be the biggest variable, not 
to mention the proper calculation and offset of antenna cable 
attenuation/length.

I would be curious how the older Thunderbolt units compares to a newer 
technology receiver/timebase in the "real world".

Just a thought





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