The Keysight 3561A is a versatile, single channel, real time spectrum analyzer with applications in electronics, vibration analysis, and acoustics. It is actually several instruments in one, operating in both the frequency domain and the time domain. In the frequency domain it serves as a spectrum analyzer with ± 0. 15dB amplitude accuracy and 2 degrees triggered phase accuracy. Utilizing the builtin tracking noise source, it also can serve as a network analyzer. (Trace math can be used when phase response or high accuracy is desired.) Digital signal processing allows the 3561A to digitally synthesize 1/3 or 1/1 octave filters, providing a high accuracy, drift free octave analyzer. Operating in the time domain the Keysight 3561 A can be used as a low frequency digital storage oscilloscope. The 3561A contains a 40k sample time buffer and complete triggering flexibility, so waveform recording is easy. Time or frequency measurements can be stored in an optional nonvolatile "bubble" memory for later analysis. Annotated hardcopy is easily obtained by pressing "plot". . . the 3561A will control HPGL plotters and raster dump printers directly. All of these capabilities in one portable instrument make the 3561A a powerful addition to any bench, and with a standard HPIB interface, the 3561A makes an excellent systems instrument as well.
Keysight 3561A Features
 Spectrum and network analysis, waveform recording, 1/3 and 1/1 octave analysis
 High accuracy, ± 0.15dB
 80 dB dynamic range and full alias protection
 High speed (7.5kHz Real Time Rate)
 Band selectable zoom analysis for 640 μHz resolution
 Full CRT annotation and softkey easeofuse
 Autoranging, autocalibration, autoscaling
 Internal nonvolatile memory stores 2 traces and 6 states. Optional bubble (nonvolatile) memory stores 127 traces and states.
Keysight 3561A Specs
Frequency 
Range: 0.000125 Hz to 100 kHz 
Realtime Bandwidth: (Typical) single display, 3 kHz; fast average display, 7.5 kHz 
Amplitude 
Measurement Range: +27 to 120dbV noise floor (22.4 VRMS to 1μV noise floor) 
Dynamic Range: 80 dB 
Input 
Impedance: 1 Mohm ± 5% shunted by 95 pF maximum. 
Isolation: Input low may be connected to chassis ground or floated up to 30 volts rms (42 volts peak) above ground. 
Coupling: Signal may be ac or dc coupled. Low frequency 3dB point <1 Hz in ac mode. 
Output
Source:

Bandlimited, bandtranslated, psuedorandom, random,
or impulse, or TTL "synch" 
Display
General: 
Magnitude. phase, time, and math traces can be selected.
Units available are:
 Horizontal: Hz, seconds, RPM, orders; linear, or log spacing
 Vertical: dBV, dBm (selectable Z), volts, volts squared, and userdefined units.

Math 
Arithmetic operations can be performed on new or recalled
frequency spectra. Add, subtract, multiply, divide, integrate,
differentiate, and userdefined constants are provided. 1 B/W is
provided for Power Spectral Density (PSD) computations 
Internal Memory 
Standard Nonvolatile: 2 traces, 6 states 
Standard Volatile: 40 time records 