HP 8901B

Model 8901B Operation
3.8 SPCL 3.8SP
Filters, RF and IF
IN
2.5 MHz
Low- Pass
455 kHz
FUNCTIONS
Special bction 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 10 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 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 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 nned RF level measurements.)
PROCEDURE
To select a desired combination of FW 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