HP 8901B Operation And Calibration Manual page 223

Model 8901B Operation
RF Input Frequency
FUNCTIONS
FREQ
DESCRIPTION
The Modulation Analyzer can measure RF input signals from 150 kHz
to
1300 MHz. (Higher
frequencies can be measured using an external mixer as described in Requency
Offset
Control on
page 3-225.)
To count input frequencies between 2.5 and 1300 MHz, the Modulation Analyzer uses heterodyning;
to
count input frequencies from 150 kHz to 2.5 MHz, it counts the input directly.
In most circumstances, when using manual tuning and when the approximate frequency is known,
the instrument can count signals with power levels less than -60 dBm.
PROCEDURE
To make an input frequency measurement, first tune the instrument to the input signal (select
AUTOMATIC OPERATION or refer to
RF Requency ltLning on page 3-115 to learn about more
ways to tune the Modulation Analyzer.) Select FREQ.
Manual tuning will be necessary when measuring low-level signals (inputs less than -25 dBm from 150
kHz to 650 MHz or less than -20 dBm from 650 to 1300 MHz).
HP-IB PROGRAM CODE
FREQ =
M5
MEASUREMENT TECHNIQUE
For input frequencies between 2.5 and 1300 MHz, the Modulation Analyzer tunes its local oscillator
(LO) to the signal and down-converts it to an intermediate frequency (IF). The
IF
signal is amplified,
limited, and counted. The
LO
frequency is also counted. The
IF
is subtracted from the
LO
frequency
and the result is displayed.
For input frequencies below 2.5 MHz the RF input signal passes directly into the IF without
down-conversion. The
IF
is counted and displayed.
RF Input Frequency
3-111