[time-nuts] Cable length calibration
Gerhard Hoffmann
dk4xp at arcor.de
Wed Jun 29 17:26:59 EDT 2016
Am 29.06.2016 um 22:07 schrieb Gary E. Miller:
> TDR. The GPS already sends a voltage down the cable to power the
> antenna. Send a sharp down the cable and see when the reflection comes
> back.
>
> Even some of my cheap managed ethernet switches can do that.
>
What reflection? If the antenna preamp has at least a somewhat decent S22
(output return loss) there will be exactly nothing that comes back. And the
cable attenuation counts twice; GPS antennas have high gain to accommodate
a lot of attenuation.
regards, Gerhard
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