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Model
8902A
Operation
Filters, RF and IF
FUNCTIONS
Special Function
3
(RF and I F Filters)
DESCRIPTION
RF Filter.
To eliminate unwanted low-frequency signals in the R F signal path, an RF filter can be inserted.
Special Function
3
manually selects the
5.25
MHz High-Pass Filter. Since the IF generally responds
to signals below
2.5
MHz, the filter eliminates any low frequencies that might be present o n the
input.
(For
input signals between 150 kHz to
10
MHz, the filter should be switched out.)
IF Filters.
The Measuring Receiver down-converts (heterodynes) the R F input to the IF. The IF is usually
centered at
1.5
MHz for input signals
10
to
1300
MHz. (An IF of
455
kHz can be manually selected.)
For
signals between
2.5
MHz and 10 MHz, the IF is
455
kHz. Below
2.5
MHz, the signal is passed
directly into the IF without down-conversion (unless the
455
kHt I F has been manually selected).
IF filters determine the frequency response of each IF.
When the
1.5
MHz IF is selected, the IF frequency response is determined by the 2.5 MHz Low-Pass
(LP) Filter.
When the
455
kHz IF is selected, the Wide
455 kHz
Bandpass (BP) Filter determines the IF frequency
response, unless a tuned RF level measurement is made which inserts the Narrow
455
kHz
BP
Filter
in series with the other selected I F filter.
Various combinations of these filters can be manually inserted using Special Function
3.
(Special
Function
3
will override automatic filter selection for Tuned R F level measurements.)
3-259
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