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Field Sweeping with the SDA-5000: Test Point Compensation

order to perform tests without cutting off service, it is necessary to use test

points. Test points are ports that tap off enough signal for monitoring, but

leave most of the signal in the system where it is needed. Typical test points

have 20-30dB of loss between the signal being measured and the port

output.

Additionally, it is sometimes necessary to inject or read signals in locations

other than the exact point of interest. If a signal is to be injected into a

reverse amplifier, there are usually some internal amplifier losses between

the test point and the actual amp input. It is also sometimes necessary to

use external pieces of hardware to combine or split signals from the field

meter before you connect to the system being tested.

Test point compensation accounts for these factors and allows the meter to

display true system levels, even though hardware between the system and

the meter may affect what the meter really sees. For example, if a forward

test point were 30dB lower than the coax line it tapped into, normal meter

readings would be 30dB below real system levels. Using test point

compensation, you can cancel out this effect. Though this simple example

would be easy to work out in your head, more complex configurations can be

far more challenging. Meter test point compensation can help insure that you

interpret meter results correctly, with accurate results.

Test Point Compensation Configuration

NOTE: Test point compensation configuration has been

significantly changed and improved over previous

implementations. The new graphical displays for forward

and reverse test point compensation provide an at-a-

glance, simplified schematic of the test point connections

you must make and where test point losses are generated.

This information is designed to help you better see

relationships among the various entries, and to help you

enter correct data for each test point loss location.

Test point compensation allows the SDA-5000 to show actual levels in the

cable network, even though some losses exist between the meter and the

network lines. The SDA-5000 allows for separate adjustment of both forward

and reverse test point losses. The following steps show you how to configure

the SDA-5000 for test point compensation.

1. 1.To adjust and review these levels, press the and 7 stu keys to call

up the FWD COMPENSATION screen shown in Fig. 4-1. (You can

also use the NAVIGATOR interface’s TESTPOINT item to get to the

FWD COMPENSATION screen.)

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Wavetek 147 Spezifikationen Seite 84