[time-nuts] ThunderBolt question

[Dana Whitlow]

Robert,

One does not know what the RF input impedance of the unit is unless one
measures it (very carefully at low levels) with a VNA or similar instrument.

Just 'cause some manufacturer says that it's 50 ohms does not mean very
much- it's not uncommon to see actual impedances off by a factor of 1,5:1 or
even 2:1.  I've heard of people using 75 ohm line with F connectors at both
ends to connect an antenna to a GPS receiver and claim that it causes no
problems.  The nice thing about 75 ohm line with F connectors is that it's
readily available in various lengths at your friendly local brick and mortar
stores.

I'd just try it and see how it works.  Then look deeper only if you come to
suspect that the GPS unit's performance is not up to snuff.

Dana     (K8YUM)


On Fri, Jun 5, 2020 at 6:22 PM Robert DiRosario <ka3zyx at comcast.net> wrote:

> I have a Trimble ThunderBolt GPSDO that I just received. It has an F
> connector for the antenna input, and BNC connectors for the 1 pps and 10
> MHz outputs. Is the receiver input impedance really 75 Ohms, or is it 50
> Ohms and they just used the F connector to distinguish it from the
> others? What do people do, just use a 50 Ohm antenna?
>
> Thanks
>
> Robert DiRosario
>
> KA3ZYX
>
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