[time-nuts] Non-impedance matched antenna cables

[Bruce Griffiths]

phil wrote:
> 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.
>
>   
All GPS receivers have larger height errors than latitude and longitude 
errors.
> 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
>
>   
Read the posted paper.
The error in determining the position using modulation on the GPS 
carrier can be much larger than the cable delay variations.
The effect will also depend on the correlator type used.

Also for those that have better receivers like the M12+T, MI2M T etc, 
every last nanosecond of variation matters.
The more that is known about cable instabilities etc, the better chance 
one has of actually realising the potential performance of a receiver.

There is no point in using impedance transformers until the actual 
impedance of the receiver and antenna are known.

Bruce