4-3
The directional coupler on the input side should be designed for at
least the frequency range of the forward bandwidth of the network
under test. (This coupler network should never be connected to the
system without the 3SRV attached, or the resulting lack of isolation
may cause signals from the forward path to bleed over to the reverse
path.)
Figure 2. Single Cable - Split Band Network Reverse Sweep
Configuration With Directional Test Points.
Another common architecture, which is only slightly different from
those described above, prescribes the use of fiber optics to "nodes".
In these architectures the installation of the 3HRV in the headend is
as shown in figure 3. The connection at the node may be as shown in
figure 4. Notice that in this configuration the forward and reverse test
points are separated, and two directional couplers must be used. In
all of these connection scenarios, either a summing network or two
directional couplers are used to interface with the system test points.
Care should be taken to use the same interface at each test point to
ensure that the normalization process is cancelling out any response
variation caused by the interface.
It is also important to remember not to make absolute level measure-
ments through the summing network due to the insertion loss and
frequency response characteristics of the interface.
Summary of Contents for 3HRV
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