Wavetek 3ST Specifiche Scaricare il pdf (Pagina 86)

5-3

Systems with directional test points are set up as shown in figure 2.

In this configuration the DDC-20 is used to provide a sample of the

reverse sweep output to the input of the 3SR receiver.

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 transmitter in the

headend is slightly modified, as shown in figure 3. Notice that a

diplex filter is used on the input of the 3ST Transmitter. This

provides optimal isolation between forward paths and minimal

insertion loss. 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 or the DDC-20 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.

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Wavetek 3ST Specifiche Pagina 86