Brüel & Kjær 1049/1051 Sine/Noise Generators

Uses

• Wide-range, 1 mHz resolution, signal generators for electronic design, instrument test and repair.
• Bus controlled, quality-control and production-line testing of electrical and mechanical products.
• Swept-frequency measurement and synchronized recording of amplitude, phase, and distortion response of audio recording and reproducing equipment, telephone systems, hearing aids, microphones, loudspeakers, and hydrophones.
• Excitation source for building-acoustic measurements, vibration testing of mechanical structures and components, plus psychoacoustic, medical, and biological research.

Features

• 0.2 to 200,000 Hz, digitally controlled, sine generators with frequency resolution down to 1 mHz and clock stability better than ±5 x 10⁻⁶/year.
• Six-decade frequency sweep in one continuous range with selectable lower and upper limits.
• Choice of linear and logarithmic frequency sweep with sweep rates from 0.001 Hz to 999.9 kHz/s and 0.001 mDec to 2 Dec/s respectively.
• Single, repetitive (1-99), and continuous sweep modes with 0.01 to 100.0 s pause between sweeps.
• Calibrated output from 100 μV to 5V with less than -96 dB harmonic and spurious distortion.
• 1024 point amplitude memory, with automatic amplitude interpolation, for preconditioned test excitation.
• 40 character, alphanumeric, line display for monitoring and setting-up of frequency and amplitude sweep parameters.
• 9 set-ups for recalling frequently repeated excitation test and measurement sequences.
• Versatile IEEE/IEC bus for remote control and digital output of data.
• Remote control functions for synchronous operation of Level and X-Y Recorders.

Additional Features (Type 1049)

• Narrow-band random, white, and pink noise modes.
• Logarithmic amplitude sweep with sweep rates from 0.1 to 999 dB/s.
• 126 dB compressor circuit for active control of sound or vibration level at exciter output.
• Automatic learn mode for amplitude memory, via compressor.

Block Diagram Description (Fig. 1)

A simplified block diagram illustrates the B&K Generators Type 1049 and 1051. The system comprises six main sections: a Master Clock, a Digital Frequency Synthesizer, a Phase Lock Synthesizer, a Sweep Synthesizer, and an Output Section, all managed by a Microprocessor Section. The Type 1049 additionally features a Noise Generator and Compressor, expanding its application range for acoustic and vibration measurements.

Frequency Synthesizer

The generators utilize a heterodyne synthesis technique. A 500 kHz fixed frequency is mixed with a 500 to 700 kHz variable frequency to produce a swept-frequency sine-wave output from 0.001 Hz to 200 kHz, with a frequency resolution of 1 mHz. The fixed 500 kHz frequency originates from the Master Clock, while the variable frequency is derived from a 5 to 7 MHz output of a Phase Lock Synthesizer. The Master Clock is based on a highly stable 10 MHz crystal oscillator, ensuring accurate frequency transfer. For enhanced accuracy, the internal oscillator can be phase-locked to an external reference signal via the Ext. Synch. socket.

Output Section

The 5 to 7 MHz control frequency from the Phase Lock Synthesizer is fed to a second 10:1 frequency divider at the input of the Output Section's mixer. This output is then mixed with the 500 kHz Master Clock output to generate a sine-wave signal whose frequency directly corresponds to the displayed value. A 280 kHz low-pass filter is employed to remove unwanted side-band components. Before reaching the outputs, the filtered signal is conditioned by an attenuator and amplifier. The output attenuator provides 16 bits of attenuation, allowing accurate setting of output levels from 100 μV to 5.00 V RMS via front panel controls or the interface bus. Two low-impedance signal outputs are available at BNC sockets on the front and rear panels, which can be matched to 50 Ω signal lines. These outputs can be isolated or connected to chassis using a rear panel slider switch for individual grounding requirements.

Amplitude Linearity and Distortion

Particular attention has been paid to achieving very low signal distortion and good amplitude linearity. At frequencies between 20 Hz and 20 kHz, the maximum harmonic and spurious distortion is better than -96 dB. Typical second and third harmonic distortion components are -105 dB down at 800 Hz. The output amplitude linearity is better than ±0.05 dB between 20 Hz and 20 kHz, decreasing to ±0.2 dB at 0.2 Hz and 200 kHz. At lower frequencies, amplitude falls by 20 dB per decade. However, by using the "Memory Learn" function to maintain a constant output level of 300 mV or less, a flat amplitude characteristic can be maintained down to 0.001 Hz.

Sweep Synthesizer

The Sweep Synthesizer includes a ramp register that generates a 31-bit output representing the generator's frequency setting. Frequency can be set via the front panel keyboard or the interface bus. For frequency sweeps, an internal clock signal is used, enabling selection of "Linear" or "Logarithmic" sweeps with rates from 0.001 Hz/s to 999.9 kHz/s (linear) and 0.001 mDec/s to 2 Dec/s (logarithmic). Both linear and logarithmic sweeps can cover six or more frequency decades in a single range. Sweep limits are independently settable within these ranges. The synthesizer supports "Up", "Down", "Up/Down", "Single", "Repetitive" (1-99), and "Continuous" sweep modes, with an optional pause function (0-100 s) between sweeps. A key feature is the automatic calculation and display of sweep time based on selected limits and rates. Minimum sweep time for repetitive Up/Down sweeps is 8 ms, while sweeps with pauses or in one direction can achieve times as short as 62.5 μs.

Amplitude Memory

The Sweep Synthesizer also contains an amplitude register for controlling the Output Section Attenuator. The output level can be set manually via the keyboard or digitally via the interface bus. The "Memory Learn" function allows up to 1024 amplitudes to be stored for successive frequencies within any desired range, enabling the generation of almost any type of amplitude-weighted frequency sweep. This function is particularly beneficial for swept frequency sound and vibration measurements, allowing output levels to be weighted according to the exciter's dynamic response for a constant sound pressure or vibration level. Automatic amplitude interpolation between consecutive amplitudes can be used to simplify data entry. Alternatively, amplitudes can be entered as a voltage signal via the 1049's Compressor Input.

Noise Generator (Type 1049)

The Type 1049 generates wide-band, pseudo-random noise with even spectral density using two long shift registers followed by low- and high-pass filters. The noise signal exhibits a symmetrical Gaussian amplitude distribution up to 4.5 σ. Nine combinations of white noise can be obtained by selecting filter frequencies, ranging from 2.2 Hz to 200 kHz, using 3-pole Chebyshev filters with less than 0.1 dB ripple and an 18 dB/octave roll-off. Pink noise is produced by filtering the white noise signal with a -3 dB/octave filter. For swept-frequency, narrow-band noise output, the white noise signal is fed to a balanced modulator circuit, producing two DC to 1.25 kHz noise signals with 90° phase difference. These signals are then combined and processed to create a swept-frequency, narrow-band noise output. Due to its high crest factor, noise outputs are attenuated by 12 dB (factor of 4) relative to the sine output, with the generator automatically accounting for this in the displayed output level.

Compressor (Type 1049)

The Type 1049 includes a Compressor to maintain a constant output level when driving loudspeakers or vibration exciters. It uses a live control signal from an external preamplifier and measurement transducer to automatically regulate and weight the generator's output level according to the exciter's dynamic characteristics. The compressor consists of an Input Attenuator, RMS Detector, VCO, and Voltage Comparator. The VCO generates a variable-frequency clock signal proportional to the input signal's rate of change, controlling the Output Attenuator. The Comparator determines whether compression is needed to maintain a constant excitation level. The compressor offers regulation over a 126 dB range relative to the maximum output level of 5 V RMS and is effective for both random noise and sine wave outputs. Compression amount is adjustable, and eight compressor speeds are available, ranging from 0.3 to 1000 dB/s.

Amplitude Sweep (Type 1049)

The Type 1049 offers a logarithmic amplitude sweep, useful for investigating electrical limiting characteristics of audio equipment and the dynamic behavior of loudspeakers and earphones. The output level can be swept up and down with rates from 0.01 to 999 dB/s, settable in 0.1 dB/s steps. This sweep is achieved using the amplitude register of the Sweep Synthesizer to step the Output Section Attenuator. A separate clock signal determines the sweep rate. The amplitude resolution of the sweep is better than 0.1 dB.

Monitoring and Set-Up Adjustments

A 40-character vacuum fluorescent line display, along with a keyboard, facilitates convenient set-up and monitoring of control settings, frequency sweep, and output voltage limits. The display can show up to four control settings simultaneously. Four Field Select keys allow for selection and adjustment of control settings. The "Speeder" knob provides fast, continuous adjustment of parameters, emulating coarse and fine tuning knobs on analog generators.

Operating Set-Ups

Generators automatically recall the last used settings. A continuous memory stores up to 9 complete front panel setups, allowing for quick recall of frequently used test sequences. This memory is maintained by a battery, retaining setups even when mains power is disconnected, provided the generators receive 4-8 hours of use per week. Entire setups can be copied to create new ones with minimal changes. For more than 9 setups, external storage via digital tape or disk is possible, with input via the digital interface.

Interfacing

Auxiliary Outputs

A square wave output is available, providing a 1 mHz to 200 kHz TTL signal corresponding to the generator's frequency setting, ideal for pulse testing electronic equipment. Fixed (5 MHz) and variable (5-7 MHz / 50-70 MHz) frequency outputs serve as clock references for external equipment. An external Sync Input accepts a 10 MHz signal or sub-harmonic for phase-locking the internal clock.

Examples of Use

The Sine Generators Types 1049 and 1051 are versatile tools for electronic design and development, quality control, production testing, and service due to their high performance, wide frequency/dynamic ranges, accuracy, resolution, stability, and extensive remote control capabilities via the IEEE/IEC digital interface. They are ideal swept frequency signal sources. The Type 1049's noise output and compressor facilities are particularly useful for electro-acoustic and building acoustic investigations, as well as vibration testing of mechanical components and structures. Brüel & Kjær offers a range of analog and digital equipment, including digital voltmeters, phase meters, frequency analyzers, and signal analyzers, that can be integrated with the 1049/1051 for comprehensive measurement systems. These systems can be controlled via terminals, personal computers, or system controllers with IEEE/IEC interfaces, enabling automated testing and analysis. Personal computers can also be used for reformatting measured data and diagnosing faults.

Specifications Summary

Diagram Descriptions

• Fig. 1: Simplified block diagram of the B&K Sine/Noise Generator Type 1049 and Sine Generator Type 1051: Illustrates the internal architecture, showing connections between the Master Clock, Frequency Synthesizers (Digital, Phase Lock, Sweep), Output Section, Microprocessor, Noise Generator, and Compressor.
• Fig. 2: Ext. Synch. Input of the 1049 and 1051 Generators: Shows the rear panel socket for external synchronization signals (1-10 MHz) and the Chassis/Floating switch for output grounding.
• Fig. 3: BNC Output and Chassis/Floating switch of the 1049 and 1051: Depicts the BNC output connector and the switch for selecting output grounding modes.
• Fig. 4: Pass band of the 1; 3.16; 10; 31.6; 100 and 316 Hz narrow-band noise bandwidths of the 1049: A graph showing the frequency response curves for different narrow-band noise filter settings, illustrating the passband characteristics.
• Fig. 5: Vacuum fluorescent line display, plus the field select and speeder controls of the 1049 and 1051: Shows the front panel layout, highlighting the alphanumeric display, control keys, and the 'Speeder' knob for parameter adjustment.
• Fig. 6: The Setup Mode, Sweep and Signal keys of the 1049: Details the front panel keys used for selecting operating modes, sweep parameters, and signal types.
• Fig. 7: The Recorder and Digital Interface connectors of the 1049 and 1051: Illustrates the rear panel connectors for interfacing with recorders (Level, X-Y) and digital systems via the IEEE/IEC bus.
• Fig. 8: The Fixed and Variable Freq. Outputs, plus the Ext. Synch. Input: Shows the rear panel connectors for auxiliary frequency outputs (5 MHz fixed, 5-7 MHz variable) and the external synchronization input.
• Fig. 9: Instrument arrangement for frequency response and phase measurements on audio recording and reproducing equipment. Using their internal memory for preconditioning, the 1049 and 1051 Generators can simulate a record pick-up, tape head, preamplifier equalization network output etc.: A block diagram showing how the generators can be integrated with other Brüel & Kjær instruments (Phase Meter, Volt Meter, Personal Computer, Graphic Plotter, Level/X-Y Recorder) for comprehensive measurement setups.
• Fig. 10: Harmonic and intermodulation distortion measurements using the 1049 or 1051 Generator with the 2033 High-Resolution Signal Analyzer: A diagram illustrating a test setup for measuring harmonic and intermodulation distortion, connecting the generator to a signal analyzer via an IEEE/IEC interface.
• Fig. 11: Simulated free-field measurements on electro-acoustic devices using the noise output and Start/Stop function of the 1049 Generator to create random noise bursts. Using the 1049 amplitude sweep, a similar arrangement may be used for measuring the attack and release time of telephone equipment, loudspeakers etc.: A diagram showing a test setup for electro-acoustic measurements, utilizing the generator's noise output and amplitude sweep capabilities with a microphone assembly, dual channel signal analyzer, and graphics plotter.