Filters, Rf And If; If Filters - HP 8901B Operation And Calibration Manual

Model
8901B
Operation
3.8 SPCL 3.8SP
Filters, RF and IF
IN
2 . 5
MHz
Low- Pass
455 kHz
FUNCTIONS
Special b c t i o n 3 (RF and
IF
Filters)
DESCRIPTION
RF Filter
To eliminate unwanted low-frequency signals in the RF 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 on the input. (For input
signals between 150 kHz to 1 0 MHz, the filter should be switched out.)
IF Filters
The Modulation Analyzer down-converts (heterodynes) the
RF
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 kHz IF
has
been manually selected).
IF
filters determine the frequency response of each
IF.
When the 1 . 5 MHz
IF
i s selected, the IF frequency response is determined by the 2 . 5 MHz Low-Pass
(LP) Filter.
When the 455 kHz
IF
is selected, the 455 kHz Bandpass (BP) Filter determines the
IF frequency
response.
Various combinations of these filters can be manually inserted using Special F'unction 3 . (Special
Function 3 will override automatic filter selection for n n e d
RF
level measurements.)
PROCEDURE
To select a desired combination of
F W
and
IF
filters, or
to
re-enter the automatic selection mode, key
in the corresponding Special Fhction code, then press the SPCL key
:
Filters,
RF
and IF
3-229