General Specification 

Modes:

Source, Echo Repeat, Transpond, Sequence, Receive

Transmit Bandwidth:

 30Hz to 200kHz

Source Level:

Up to 185dB re 1µPa @ 1m (3kHz to 200kHz)

Horizontal Beam Pattern:

Omnidirectional

  Source Mode  

Pulse lengths:

3ms to 10s or CW (below 17.5 kHz)

Number of pulses:

Up to 1000

Pulse intervals:

Up to 60s

Variable step levels:

-10 to +10dB

Tones:

Up to 24 (each with definable source levels and frequencies, with up to 5 Noise bands - CW or pulsed)

Sweeps:

LFM or LPM

Noise:

Either broadband or up to 5 user definable bands

Noise types:

White, Pink or Pseudo-Random

Modulated signal:

AM or FM (user definable carrier and modulating signal)

In Echo Repeat mode, VASS can repeat acoustic signals (between 300Hz and 12.5kHz) sampled from the dedicated receiver hydrophone contained in the towed body. It does this in response to a trigger event, based either on the incoming acoustic signal, an external input, or under operator control. The repeated signal can have a highlight structures and Doppler shift imposed upon it to mimic the reflections from a moving or stationary target.

The many configurable parameters are controlled via an easily operated Graphical User Interface, running under Microsoft Windows 98. Within this interface, the user can add Doppler, target strength and signal highlights to the echo repeated acoustic signal. Subsequent echo repeated signals could, in addition to the above, simulate a moving target track.

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  Echo Repeat Mode 

Echo frequency:

Broadband (300Hz to 12.5kHz) or  3 narrow bands

Trigger types:

Acoustic, TTL pulse or manual

Trigger level and averaging:

Fully user definable

Echo length:

10ms to 5s

Added doppler:

-40 to +40 knots

Added echo strength:

- 30 to +40dB

Echo delay:

Up to 60s

Highlights:

Up to 5

Highlight strength:

-30 to +30dB

Highlight offset:

Up to 200ms

Moving track target :

Start range up to 90km Velocity, -40 to +40 knots

Tag on transponder:

User configurable

Transponder 

In Transpond mode, VASS can transmit a user defined acoustic signal in response to a trigger event which can be either acoustic, from an external input or under operator control. The transpond signal can be defined (300Hz to 12.5kHz only) as a single pulse, or a ramp of pulses, of a monotone or LFM or LPM sweeps, with selectable frequency and source level.  In addition, any selection within the Source Mode can be transponded allowing signals from 30Hz to 200kHz to be transponded.

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  Transpond Mode 

Frequency range:

Receive - 300Hz to 12.5kHz
Transmit - 30Hz to 200kHz

Trigger types:

Acoustic, TTL pulse or manual

Trigger level and averaging

Fully user definable

Transpond types:

LFM or LPM sweep Monotone
or as per Source Mode

  Sequence Mode 

Pulse Types:

Tones, Noise, LFM or LPM Sweeps, modulated signal or pulse trains

Pulse Trains

Up to 1000

Pulse Lengths:

Up to 10s each

    Receive Mode 

Frequency Range:

300 Hz to 12.5kHz or through band pass filter

Slant Range Processor 

In DME (Distance Measuring Equipment) mode, VASS can transmit or receive underwater acoustic tracking pulses. This system is used to measure the slant range between the towed body of VASS & the vessel under test. So that the vessel under test can display the 

slant range a Remote DME unit is provided which has all the digital signal processing and synchronisation equipment mounted within a PC.The configurable parameters are controlled via an easily operated Graphical User Interface, running under Microsoft Windows 95/98/NT4.
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  Slant Range (DME) System: 

Type

Synchronised ranging system

Frequencies:

Selectable depending on the vessel's sonar

Synchronised:

Via VHF radio to vessel under test

Oscillator:

Highly stable oven controlled oscillator

 Remote DME System:             

PC:

Portable mains powered PC with LCD screen

Cards included in PC:

DME processor and DME DSP card

Software

Remote DME User Interface, running under Microsoft Windows 95-98

Printer:

Portable ink jet

Interface to sonars:

Transmit via (for example) underwater telephone system or separate transducer(s). Receive via a suitable sonar's bus (with a separate interface unit) or underwater telephone or separate transducer(s).

Synchronisation:

Interface to vessel's VHF radio set

 Surface Operations Cabin:      

Size

Half size ISO container (3.0m x 2.4m x 2.4m high)

Power input:

3 phase 380V 50Hz, or 415V 50Hz, or 440V 60Hz

Climate control:

Air conditioning and heating

Standard Equipment:

Two 19 inch racks containing a complete set of VASS electronics and a complete backup set. Each set includes: DSP card, Band pass filter card, DC/DAC card, DME processor card, DME DSP card, 1.2kVA Power amplifier, HF Power Amplifier, Pentium PC, 14" monitor, Keyboard, Printer, VHF Radio, Digital Analyser.

Tow Fish:  

Tow speed:

2 to 8 knots

Size

Wingspan: 1.4m Length: 1.4m Height: 0.6m

Weight:

195kg in air

Within tow fish:

Transmitting transducers, Receive hydrophone, Monitor hydrophone and tow fish electronics.

  Tow Fish Electronics  

Telemetry:

Pitch, roll, heading, depth and temperature all displayed on the Windows interface in the Surface Operations Cabin and recorded in a log file).

 Receive Hydrophone   

Calibrated for receive and echo repeat.
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 Monitor Hydrophone  

For monitoring all transmissions
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 Transmit Transducers  

Number:

4

Frequency bands:

30Hz to 17.5 kHz
17.5 kHz to 50 kHz
50 kHz to 110 kHz
111 kHz to 200 kHz

Source level:

Up to 185dB re 1mPa @ 1m

Horizontal response:

Omnidirectional

 Winch  

Size:

2m x 1.6m x 1.6m high

Power input:

3 phase 380V 50Hz, or 415V 50Hz, or 440V 60Hz

  Tow Cable  

Diameter:

12.7mm

Length:

1000m

Portable Echo Repeater System 

The Portable Echo Repeater System (PERS) is a compact and versatile system for the performance evaluation of a wide range of active and passive sonar.  PERS has been designed to be hand-deployed from small vessels with few facilities - the transducer assembly is a small lightweight unit containing both projector and hydrophone.  The surface end of the system includes a rugged, portable, power amplifier unit and a controlling computer. 

PERS includes many of the powerful features of the Chelsea Technologies Group Versatile Acoustic Source System (VASS) but without the complexity of a towed format obviating the need for larger vessels. PERS is controlled by an easy-to-use Graphical User Interface commanding the Digital Signal Processor which is used to Echo Repeat, Transpond, and produce Calibrated transmissions with up to 24 Tones simultaneously.

PERS provides a highly versatile and flexible sonar test system that is configured by simple mouse or keyboard selections. In addition to instant configuration changes, via its Microsoft Windows 98 interface, PERS allows desktop set-up of complete trials programs in advance hence avoiding costly errors in signal definition during calibration trials.

Portable Echo Repeater System datasheet

Existing users of the ERAS, VASS & PERS systems include QinetiQ, the UK Director of Submarines, NATO SACLANT Undersea Research Centre, La Spezia, Italy, the Belgian Navy & EDO Corporation, USA
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  Specification - General (applies to all modes) 

Modes

Source, Echo Repeat,Transpond, Sequence, Sequence (Advanced System)

Transmit Bandwidth

5.5kHz to 9kHz (180dB operation)

Horizontal Beam Patterns

Omnidirectional

Vertical Beam Patterns

± 30°

Specification - Source and Sequence Modes

As a calibrated acoustic test, signal transmitter (source mode) PERS can generate complex acoustic test signals (between 5.5kHz and 9kHz).  It is capable of concurrently generating up to 24 tones.  An advanced version of the system also allows up to five noise bands (selectable from white, pink or pseudo-random noise) to be generated with the tones. The frequency and source level of each tone (and noise band) may be controlled independently and each selected as CW or pulsed. PERS can also generate LFM or LPM sweeps and complex modulated acoustic transmissions.  The advanced system includes a sequence mode allowing the user to program a series of pulse trains giving up to 12,500s of continuous programmed sequenced transmissions, for example 250 uniquely specified pulse trains each with 1000 50ms pulses can be specified.

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Specification - Echo Repeat Mode

In Echo Repeat mode, PERS can repeat signals (between 5.5kHz and 9kHz) sampled from the receive hydrophone contained in the, hand-deployable, Transducer head. It does this in response to a trigger event, based either on the incoming acoustic signal, an external input, or under operator control.  The repeated signal can have a highlight structure imposed upon it to mimic the reflections from a target. The many configurable parameters are controlled via an easily operated Graphical User Interface, running under Microsoft Windows 98. Within this interface, the user can add Doppler, target strength and signal highlights to the echo repeated acoustic signal. Subsequent echo repeated signals could, in addition simulate, a moving target track.