Overview; Description - Keysight 778D Operating And Service Manual

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Overview

Description

This coaxial dual directional coupler has a frequency range extending over four octaves from 100
MHz to 2 GHz. Although the coupling factor increases
6 dB/octave below 100 MHz, directivity remains above 36 dB. Thus, the coupler can be used below
100 MHz as well as above. The usefulness below 100 MHz is restricted only by the amount of signal
source power and/or the sensitivity of the RF detector connected to the coupler.
The unidirectional characteristic of the Keysight 778D dual directional coupler makes it an
important tool in microwave measurement systems. The 778D has the property of inducing, in an
auxiliary line, a contra-directional flow of power which is proportional to the power flowing in the
main guide. This coupler may be used in the measurement of reflection coefficients or SWR over a
very wide frequency range. The relatively constant coupling across several frequency bands and
the stability of coupling with time make the 778D useful, also, as a wideband attenuator or for
power monitoring applications.
To achieve its broad frequency coverage, the 778D's directivity is optimized for mainline energy
flowing in one direction. This means that there is a preferred orientation for the 778D. To achieve
the measurement accuracies in the specifications, the test device or system should be connected
where the 778D is labeled TEST PORT. To accommodate test devices with Type N or APC-7
connectors, a choice of connectors is available on the TEST PORT (see Options outlined in
Chapter 2,
With the APC-7 precision sexless connector on the output, the coupler can be conveniently
converted to other types of connectors by the use of an adapter. Adapters are available to the SMA
(OSM), TNC, GR900, and others, so that the coupler becomes a versatile device for making
measurements on many different types of connectors. The Amphenol APC-7 is a sexless connector
with very low SWR. This precision connector makes possible the construction of adapters with low
SWR.
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"Specifications").
Keysight 778D Operating and Service Manual