[time-nuts] 75Z vs 50Z for GPS receivers (was Re: ACE-III GPS receivers (Dr Bruce Griffiths))

[Christopher Hoover]

> Most (except for Trimble,..) GPS receivers and antennas
> are designed to use 50 ohm cable.
> Trimble Bullet GPS antennas have a 50 ohm output impedance.
> Trimble literature however is ambiguous in that in the
> Resolution T receiver datasheets talk about using RG59
> to connect to the antenna.

FWIW, the Thunderbolt manual says this on page 3-5:

--------
Note - RG-59 is a 75 ohm coaxial cable. The ThunderBolt and
the Bullet antenna are compatible with either 50-ohm or 
75-ohm cable. Compared to most 50 ohm cable, 75 ohm cable
provides superior transmissibility for the 1.5 GHz GPS
signal and a better quality cable for the price. Mismatched
impedance is not a problem.
--------
--------
Note - The input impedance of the ThunderBolt RF input &
its antenna is 50 ohms.
--------


I would also add that BNC and N connectors come in both 50Z and 75Z flavors.
In fact 75Z BNC connectors are pretty common, being used in professional
video applications.  (Check surplus BNC patch cords carefully.)  On the
other hand, 75Z N connectors are much less common, but were used in CATV
plants, IIRC.

-ch