Tektronix WFM5200 Instructions Manual page 24

Basic Installation Procedure
Line Termination
Compatibility of BNC
Center Pins
18
Your instrument uses a passive loop-through reference input. Accordingly, the
loop-through input must be terminated externally. It is important that this external
termination meets accuracy and return loss requirements.
If the instrument is installed to monitor an operating link, the destination receiver
and the connecting cable serve as the termination. This monitoring connection
checks the performance of the entire path. The return loss of the instrument is
sufficiently high that, in most cases, the destination receiver sets the system return
loss.
In cases where the instrument is placed at the end of a link, a BNC termination
must be installed on one side of the loop-through reference connector. The
termination must be 75 Ω and DC coupled (good return loss extends to DC). An
appropriate termination for the EXT REF connector is Tektronix part number
011-0163-00; this is a 75 Ω, End-of-Line termination.
Most BNC connectors for video equipment, whether 50 Ω or 75 Ω, use a 50 Ω
standard center pin. Some laboratory 75 Ω BNC connectors use a smaller
diameter center pin. The BNC connectors on the instrument are designed to work
with the 50 Ω standard (large diameter) center pins.
Do not use connectors or terminators with the smaller center pins. They could
cause intermittent connections.
WFM5200 Installation and Safety Instructions