Selective Power Measurements (Option Series 030) - HP 8901B Operation And Calibration Manual

Model
8901B
Operation
Selective Power Measurements (Option 030)
FUNCTIONS
Special Functions 23 (External LO) and 24 (Selective Power Measurements)
DESCRIPTION
The Series 030, Selective Power Measurement Options enable the Modulation Analyzer to measure
adjacent-channel power and single-sideband noise on continuous wave (CW) RF signals. Both
measurements basically consist of tuning the instrument to the RF signal, measuring the IF level
in the passband of a selected IF filter, then offsetting the signal onto the skirt of the IF filter and
re-measuring the IF level. Offsetting the signal places a portion of the sideband noise of the carrier in
the passband of the IF filter. The ratio of the out-of-band IF level to the in-band IF level
is
the desired
measurement result (expressed in
dB).
The measurement procedure requires that the operator step through a sequence of special functions
and increment either the local oscillator (LO) or the signal source. For RF signal frequencies above
300 MHz, an external LO is recommended for greatest sensitivity and accuracy. Special Function 23
switches the LO between internal and external. The external LO connects to a rear-panel connector.
(Since Option Series 030 provide rear-panel LO input and output connectors, Option 003 is not available
in conjunction with the 030 Series Options.)
The 030 Series Options include the choice of two IF
bandpass filters installed. The bandwidths of these
IF filters match the requirements of specific industry standards for measuring adjacent-channel power.
The following table lists the optional filters and their bandwidths.
I
Filters
I
ODtions
I
12.5
kHz
Adjacent Channel Filter
25
kHz
Adjacent Channel Filter
30
kHz
(Cellular Radio)
Filter
Option 032
Option
033
Option 035
Carrier Noise
Filter
Option 037
All selective power measurements consist of three processes. The first two are identical for either
adjacent channel power or single-sideband noise measurements. However, the third step is different
depending on the measurement being made:
1. Setting up the
LO:
Put the Modulation Analyzer in its selective power measurement mode. If using an external LO,
enter an
LO value into the Modulation Analyzer that is offset 455 kHz from the incoming signal.
If using the Modulation Analyzer's internal LO, just tune to the input signal.
2. Setting the reference:
Measure the voltage reference and set that reference to be 0
dB.
(Adjust the LO frequency to
ensure that the peak value is being measured.) Then measure the peak voltage reference and set
it to be 0 dl3.
3a. Measuring the adjacent channel power:
T h e the LO to the 6 dE3 point of the filter and move the LO the spacing required for the
appropriate adjacent channel filter.
3b. Measuring the single-sideband noise:
Choose whether to display the data as total power in the 2.5 kHz filter bandwidth or as dBc in
a 1
Hz bandwidth. Tune the Modulation Analyzer
(or
the external LO) to the offset frequency
desired and measure the noise.
Selective Power Measurements (Option 030) 3-95