Applications - Keysight 775D Operating And Service Manual

Introduction
Complementary
Equipment
Error Analysis
Power Measurement

Applications

Applications
The 775D couplers are usually used in a reflectometer. Figures 3, 4, 5, and 6
illustrate typical setups. Note that a line stretcher (or a longer length of
cable) must be used with vector voltmeters or network analyzers to balance
the two signal paths in the coupler for zero phase reference.
Figure 3, 4, 5 and 6 show K eysight equipment suitable for use with the
775D couplers.
There are certain errors present in all reflectometer systems. Usually the
most significant error is that caused by the directivity of the directional
coupler. The magnitude of this error can be measured accurately over the
frequency band (see Directivity Test, page
known, the ambiguity of any measurement can be determined with the
reflectometer calculator obtainable from K eysight Technologies (part
number 5952-0948).
Error also results from multiple reflections or mismatch losses of the
components of the reflectometer system. The ambiguity introduced by this
error can also be calculated with the reflectometer calculator mentioned
above.
The 775D may also be used for measuring power as shown in
the coupler samples primary-line power and a coaxial thermistor mount is
used as a power-detecting device. The coupler can also be used for
measuring peak power up to 10 kW, provided average power remains below
the rating of the coupler (50 W) and the sampled pulses are attenuated to the
power-handling capability of the thermistor mount.
When monitoring power with this coupler keep in mind that the output
power is the coupling (20 dB nominally) above the power sampled at the
auxiliary port. For very precise work, the insertion loss of the coupler
(attenuation of primary line) must be subtracted from the calculated output
power.
6 775D Operating and Service Manual
12). Once the directivity is
Figure 6. Here