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The HP 3561A is a single-channel dynamic signal analyzer covering 0.000125 Hz to 100 kHz, designed by Hewlett-Packard for electronics, vibration analysis, and acoustics applications. The datasheet describes it as 'several instruments in one' — operating in both the frequency domain as a spectrum analyzer and in the time domain as a low-frequency digital storage oscilloscope. With a built-in tracking noise source, it also serves as a network analyzer, and digital signal processing allows it to synthesize 1/3 or 1/1 octave filters for high-accuracy, drift-free octave analysis.
The datasheet lists applications in electronics, vibration analysis, and acoustics. In noise and vibration measurements, transducers convert physical phenomena to voltage; the 3561A includes an internal power supply for ICP-type (integrated circuit piezoelectric) transducers, eliminating an extra piece of signal-conditioning equipment. A hardware A-weighting filter conforming to ANSI S1.4-1971 (R1976) is provided for acoustic measurements where human-ear response must be considered. The combination of octave and narrowband analysis on a single instrument supports noise and vibration work that traditionally required separate tools.
ValueTronics International has specialized in test and measurement equipment since 1992, with a deep inventory of legacy Hewlett-Packard instruments that remain in active use across calibration labs, machinery balancing programs, and acoustic and vibration research environments. Every unit moves through our 20,000 sq ft facility at 1675 Cambridge Drive in Elgin, Illinois — where instruments are received, inspected, and performance-tested by our technicians before they ship. For dynamic signal analyzers like the 3561A, where amplitude accuracy and phase response are the measurement, that hands-on verification step is what separates a documented working instrument from a marketplace listing.
Hewlett-Packard's test and measurement business was spun out as Agilent Technologies in 1999, and the electronic measurement portion of Agilent became Keysight Technologies in 2014. The HP 3561A predates both transitions — it carries the original HP branding from the era when the company defined precision instrumentation. Keysight continues to support many HP-lineage products through its calibration and service infrastructure.
| Specification | Value |
|---|---|
| Frequency | |
| Range | 0.000125 Hz to 100 kHz |
| Spans | 0.01024 Hz to 100 kHz in a 1, 2, 2.5, 5, 10 sequence |
| Accuracy | ± 0.003% of display center frequency |
| Resolution | 0.25% of frequency span |
| Window | Flat Top, Hann, Uniform, and Exponential |
| Bandwidth (3 dB Bandwidth, % of frequency span) | |
| Flat Top | 0.90% |
| Hann | 0.37% |
| Uniform | 0.25% |
| Real Time Bandwidth (Typical) | Single display: 3.0 kHz; Fast average display: 7.5 kHz |
| Amplitude | |
| Measurement Range | +27 to -120 dBV noise floor (22.4 VRMS to 1 µV noise floor). Input range selected in 1-dB steps from +27 to -51 dBV. Optimum range determined automatically in autorange mode. |
| Dynamic Range | 80 dB |
| Accuracy at the Passband Center | |
| +27 to -40 dBV input ranges | ± 0.15 dB |
| -41 to -51 dBV input ranges | ± 0.25 dB |
| Flat Top window | +0, -0.01 dB |
| Hann window | +0, -1.5 dB |
| Uniform window | +0, -4.0 dB |
| Note | Overall accuracy is the sum of the accuracy at the passband center plus the selected window accuracy. |
| Resolution | |
| Log | 0.01 dB |
| Linear | 4 digits |
| Phase | |
| Accuracy | ±2 degrees, dc-10 kHz; ± 10 degrees, 10-100 kHz (signals no more than 40 dB below full range) |
| Resolution | 0.1 degree |
| Input | |
| Impedance | 1×10⁶ ohms ± 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 3-dB point <1 Hz in ac mode |
| A-weighting | Hardware A-weighting filter conforms to ANSI standard S1.4-1971 (R1976) |
| ICP current | Nominal 4 mA current source provided, compatible with integrated circuit piezoelectric accelerometers |
| Output | |
| Source | Band-limited, band-translated, pseudo-random, random, or impulse, or TTL "synch" signals are available on rear panel. Level is selectable between 0.7 and 0.007 volts RMS, nominal. Impedance 50Ω ±5Ω. |
| Print/Plot | Controls HP-GL plotters and HP raster dump printers directly |
| Display | |
| General | Magnitude, phase, time and math traces may be selected. Units available are: Horizontal: Hz, seconds, RPM, orders; linear or log spacing. Vertical: dBV, dBm (selectable Z), volts, volts squared, and user-defined units. |
| Scale | Linear or log magnitude scales may be selected. Full scale, dB/division, and degrees/division are user definable. Center scale user definable in phase or time traces. |
| Math | Arithmetic operations can be performed on new or recalled frequency spectra. Add, subtract, multiply, divide, integrate, differentiate and user-defined constants are provided. 1/BW is provided for Power Spectral Density (PSD) computations. |
| Internal Memory | |
| Standard Non-volatile | 2 traces, 6 states |
| Standard Volatile | 40 time records |
| Optional Non-volatile | Traces + states + (1 + 2 × time capture records) = 127 |
| Optional Volatile | 40 time records |
| Marker | |
| Functions | Single, relative, harmonic, sideband, and power cursors are provided. THD can be calculated from up to 20 harmonics. Sideband power relative to specified carrier can be calculated from up to 10 sidebands. MKR to peak, MKR to center, MKR to full scale and marker peak track are provided. |
| General | |
| Power | 100/120 Vac +5%, -10%, 48-440 Hz; 220/240 Vac +5%, -10%, 48-66 Hz |
| Weight | 15 kg (33 lb) net, 21.6 kg (47.5 lb) shipping |
| Dimensions | 335 mm W × 595 mm D × 197 mm H (13.2" × 23.4" × 7.8") |
| HP-IB Interface Functions | Implementation of IEEE Std. 488-1978 SH1, AH1, T5, TE0, L4, LE0, SR1, RL1, PP0, DC1, DT1, C0 |
Please review the Manufacturer's Data Sheet to verify published specifications. Feedback on this webpage is always welcome — please reach out to your Test Architect at any time for questions or concerns. Thank you, we truly appreciate you being our customer.
Model No
HP
Condition
Used
Manufacturer
Agilent
Frequency
100 kHz
1
Extended Non-volatile Memory
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