12
OPTIONAL Filter Keys
The ALT key is active if optional filters are installed in the Model
8201A. Optional filters available are:
THRU
Permits connection of external filters in the audio path
CCIR
CCIR recommendation 468-3 bandpass filter
CCITT
CCITT recommendation P.53 bandpass filter
C-MSG
Bell System Technical Reference 41009 bandpass filter
Any or all of these filters can be installed at one time; however, the
A15 option board is required with any of the filters. The ALT key will
activate the filters marked above the corresponding high-pass key, if
the filters are installed. Error 19 will be displayed if an optional filter
is not installed and the key is depressed.
DETECTOR Switches
The second group of measurement control keys is the DETECTOR
switches. The peak detectors are normally used to measure modula-
tion, however, precision RMS detectors are included in the Model
8201A. These detectors are used primarily to characterize noise
residuals and complex or distorted modulation signals. Two detectors
are provided.
RMS Key
The normal function of the RMS key is to select an rms calibrated
display; however, SPCL function 18 can be executed to change the
RMS key to select rms detection calibrated in peak for sinusoidal
modulation. This is particularly useful when comparing peak and RMS
indications of noisy signals.
QUASI-PEAK Key
A quasi-peak detector, compatible with CCIR 368-3, is available for
use with the CCIR filter option. This detector is always available,
whether the optional filter is installed or not.
PEAK Keys
The Peak +, -, and ± keys, the RMS key, and the QUASI-PEAK key are
arranged such that only one detector can be selected at a time.
HOLD Key
The HOLD key is used to activate the hold detector mode. It is an al-
ternate action key which can be used with any detector. In operation,
as modulation measurements are made, the larger of the current
measurement or the previous measurement becomes the displayed
modulation. Depress the HOLD key to activate this mode, and then
depress the key again to cancel.
Other Keys
Figure-7: Other Keys of 8201A Modulation Analyzer
RATIO Key
The RATIO key is an alternate action key which changes the active
display from absolute to relative. In addition, the ratio measure-
ment can be made relative to the current display, or to a set value.
Ratio can be displayed in percent, measurement units, or dB by using
the %, units, and dB keys in the data keypad. For relative frequency
measurements use the % key or for delta frequency use kHz, MHz or
GHz keys.
AUTO key
The AUTO key is used to resume automatic operation of a particular
function. It is active for the carrier FREQ, carrier LEVEL, audio FREQ,
AM, FM, and PM functions. When numerical data is entered into a
particular function window, the LED in the AUTO key will go out. This
indicates that the selected function is not displaying a measured
value. To resume measurement, depress the AUTO key. If carrier FREQ
is the active function, depressing the AUTO key will always force the
Model 8201A to reacquire the carrier signal.
LCL(INIT) key
The LCL(INIT) key is a dual function key. If the Model 8201A is in the
local IEEE•488 bus state and the key is depressed an initialization
restart occurs. This is similar to a power on reset except that the
current instrument status is lost. This does not include bus address
or end-of-string selection. If the Model 8201A is remote enabled, and
the local lockout bus state is not active, the instrument will return to
front panel control.
STO and RCL Keys
The STO and RCL keys are used with the PRGM function key to store
and recall one of the 100 possible instrument control settings.
CAL key
The CAL key is used to calibrate the active function. It is active for
carrier LEVEL, AM, FM, and PM modulation.
