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SDA-5500/SDA-5510 Sweep Configuration: Sweep History and Theory

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receiver used for later alignments also enables cancellation of absolute

value meter errors. The absolute error at C will be almost the same as the

error at B. If B is used as a perfect reference, then any absolute level error

will be adjusted out. In order to maximize this effect, Acterna recommends

that you frequently refresh the reference to be used in sweep testing (at

least once a shift).

Test Point Compensation

In aligning a cable network, the important levels, the ones you should care

about, are the system levels within the coax and amplifiers. However, in

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 all of 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.

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Wavetek 147 Especificaciones Pagina 327